AT89LP51RD2/ED2/ID2 - Complete

Features
• 8-bit Microcontroller Compatible with 8051 Products
• Enhanced 8051 Architecture
–
–
–
–
–
–
–
–
•
•
•
•
•
Single Clock Cycle per Byte Fetch
12 Clock per Machine Cycle Compatibility Mode
Up to 20 MIPS Throughput at 20 MHz Clock Frequency
Fully Static Operation: 0 Hz to 20 MHz
On-chip 2-cycle Hardware Multiplier
16x16 Multiply–Accumulate Unit
256 x 8 Internal RAM
On-chip 2KB Expanded RAM (ERAM)
• Software Selectable Size (0, 256, 512, 768, 1024, 1792, 2048 Bytes)
– Dual Data Pointers
– 4-level Interrupt Priority
Nonvolatile Program and Data Memory
– 64KB of In-System Programmable (ISP) Flash Program Memory
– 4KB of EEPROM (AT89LP51ED2/ID2 Only)
– 512-byte User Signature Array
– Endurance: 10,000 Write/Erase Cycles
– Serial Interface for Program Downloading
– 2KB Boot ROM Contains Low Level Flash Programming Routines and a Default
Serial Bootloader
Peripheral Features
– Three 16-bit Enhanced Timer/Counters
– Seven 8-bit PWM Outputs
– 16-bit Programmable Counter Array
• High Speed Output, Compare/Capture
• Pulse Width Modulation, Watchdog Timer Capabilities
– Enhanced UART with Automatic Address Recognition and Framing
Error Detection
– Enhanced Master/Slave SPI with Double-buffered Send/Receive
– Two Wire Interface 400K bit/s
– Programmable Watchdog Timer with Software Reset
– 8 General-purpose Interrupt and Keyboard Interface Pins
Special Microcontroller Features
– Dual Oscillator Support: Crystal, 32 kHz Crystal, 8 MHz Internal (AT89LP51ID2)
– Two-wire On-Chip Debug Interface
– Brown-out Detection and Power-on Reset with Power-off Flag
– Selectable Polarity External Reset Pin
– Low Power Idle and Power-down Modes
– Interrupt Recovery from Power-down Mode
– 8-bit Clock Prescaler
I/O and Packages
– Up to 40 Programmable I/O Lines
– Green (Pb/Halide-free) PLCC44, LQFP44, VQFN44, PDIP40
– Configurable I/O Modes
• Quasi-bidirectional (80C51 Style), Input-only (Tristate)
• Push-pull CMOS Output, Open-drain
Operating Conditions
– 2.4V to 5.5V VCC Voltage Range
– -40C to 85°C Temperature Range
– 0 to 20 MHz @ 2.4V–5.5V (Single-cycle)
8-bit Flash
Microcontroller
with 64K bytes
Program
Memory
AT89LP51RD2
AT89LP51ED2
AT89LP51ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
1. Pin Configurations
44-lead TQFP/LQFP
44
43
42
41
40
39
38
37
36
35
34
P1.4 (CEX1/SS†)
P1.3 (CEX0)
P1.2 (ECI)
P1.1 (T2 EX/SS)
P1.0 (T2/XTAL1B‡)
P4.2 (XTAL2B‡)
VCC
P0.0 (AD0)
P0.1 (AD1)
P0.2 (AD2)
P0.3 (AD3)
1.1
33
32
31
30
29
28
27
26
25
24
23
1
2
3
4
5
6
7
8
9
10
11
P0.4 (AD4)
P0.5 (AD5)
P0.6 (AD6)
P0.7 (AD7)
POL
P4.0 (SCL)
P4.4 (ALE)
P4.5 (PSEN)
P2.7 (A15/AIN3)
P2.6 (A14/AIN2)
P2.5 (A13/AIN1)
12
13
14
15
16
17
18
19
20
21
22
(†MOSI/CEX2/MISO) P1.5
(†MISO/CEX3/SCK) P1.6
(†SCK/CEX4/MOSI) P1.7
(DCL) RST
(RXD) P3.0
(SDA) P4.1
(TXD) P3.1
(INT0) P3.2
(INT1) P3.3
(T0) P3.4
(T1) P3.5
44-lead PLCC
† SPI in remap mode
‡ AT89LP51ID2 Only
2
39
38
37
36
35
34
33
32
31
30
29
18
19
20
21
22
23
24
25
26
27
28
7
8
9
10
11
12
13
14
15
16
17
P0.4 (AD4)
P0.5 (AD5)
P0.6 (AD6)
P0.7 (AD7)
POL
P4.0 (SCL)
P4.4 (ALE)
P4.5 (PSEN)
P2.7 (A15/AIN3)
P2.6 (A14/AIN2)
P2.5 (A13/AIN1)
(WR) P3.6
(RD) P3.7
(XTAL2A) P4.7
(XTAL1A) P4.6
VSS
(DDA) P4.3
(A8) P2.0
(A9) P2.1
(DAC-/A10) P2.2
(DAC+/A11) P2.3
(AIN0/A12) P2.4
(†MOSI/CEX2/MISO) P1.5
(†MISO/CEX3/SCK) P1.6
(†SCK/CEX4/MOSI) P1.7
(DCL) RST
(RXD) P3.0
(SDA) P4.1
(TXD) P3.1
(INT0) P3.2
(INT1) P3.3
(T0) P3.4
(T1) P3.5
6
5
4
3
2
1
44
43
42
41
40
P1.4 (CEX1/SS†)
P1.3 (CEX0)
P1.2 (ECI)
P1.1 (T2 EX/SS)
P1.0 (T2/XTAL1B‡)
P4.2 (XTAL2B‡)
VCC
P0.0 (AD0)
P0.1 (AD1)
P0.2 (AD2)
P0.3 (AD3)
1.2
(WR) P3.6
(RD) P3.7
(XTAL2A) P4.7
(XTAL1A) P4.6
VSS
(DDA) P4.3
(A8) P2.0
(A9) P2.1
(DAC-/A10) P2.2
(DAC+/A11) P2.3
(AIN0/A12) P2.4
† SPI in remap mode
‡ AT89LP51ID2 Only
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
44-pad VQFN/MLF
P1.4 (CEX1/SS†)
P1.3 (CEX0)
P1.2 (ECI)
P1.1 (T2 EX/SS)
P1.0 (T2/XTAL1B‡)
P4.2 (XTAL2B‡)
VDD
P0.0 (AD0)
P0.1 (AD1)
P0.2 (AD2)
P0.3 (AD3)
1.3
44
43
42
41
40
39
38
37
36
35
34
† SPI in remap mode
‡ AT89LP51ID2 Only
P0.4 (AD4)
P0.5 (AD5)
P0.6 (AD6)
P0.7 (AD7)
POL
P4.0 (SCL)
P4.4 (ALE)
P4.5 (PSEN)
P2.7 (A15/AIN3)
P2.6 (A14/AIN2)
P2.5 (A13/AIN1)
12
13
14
15
16
17
18
19
20
21
22
NOTE:
Bottom pad
should be
soldered to ground
1.4
33
32
31
30
29
28
27
26
25
24
23
1
2
3
4
5
6
7
8
9
10
11
(WR) P3.6
(RD) P3.7
(XTAL2A) P4.7
(XTAL1A) P4.6
GND
(DDA) P4.3
(A8) P2.0
(A9) P2.1
(DA-/A10) P2.2
(DA+/A11) P2.3
(AIN0/A12) P2.4
(†MOSI/CEX2/MISO) P1.5
(†MISO/CEX3/SCK) P1.6
(†SCK/CEX4/MOSI) P1.7
(DCL) RST
(RXD) P3.0
(SDA) P4.1
(TXD) P3.1
(INT0) P3.2
(INT1) P3.3
(T0) P3.4
(T1) P3.5
40-pin PDIP
(T2) P1.0
(SS/T2EX) P1.1
(ECI) P1.2
(CEX0) P1.3
(†SS/CEX1) P1.4
(†MOSI/CEX2/MISO) P1.5
(†MISO/CEX3/SCL) P1.6
(†SCK/CEX4/MOSI) P1.7
RST
(RXD) P3.0
(TXD) P3.1
(INT0) P3.2
(INT1) P3.3
(T0) P3.4
(T1) P3.5
(WR) P3.6
(RD) P3.7
(XTAL2A) P4.7
(XTAL1A) P4.6
GND
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
VDD
P0.0 (AD0)
P0.1 (AD1)
P0.2 (AD2)
P0.3 (AD3)
P0.4 (AD4)
P0.5 (AD5)
P0.6 (AD6)
P0.7 (AD7)
POL
P4.4 (ALE)
P4.5 (PSEN)
P2.7 (A15/AIN3)
P2.6 (A14/AIN2)
P2.5 (A13/AIN1)
P2.4 (A12/AIN0)
P2.3 (A11/DAC+)
P2.2 (A10/DAC-)
P2.1 (A9)
P2.0 (A8)
†SPI in remap mode
Note:
1. The AT89LP51ID2 is not available in the PDIP package
3
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
1.5
Pin Description
Table 1-1.
Atmel AT89LP51RD2-ED2-ID2 Pin Description
Pin Number
VQFP
VQFN
(1)
PLCC
PDIP
Symbol
Type
I/O
I/O
1
7
6
P1.5
I/O
I/O
I/O
I/O
2
8
7
P1.6
I/O
I/O
I/O
I/O
3
9
8
P1.7
I/O
I/O
I/O
4
10
9
RST
I
4
Description
P1.5: User-configurable I/O Port 1 bit 5.
MISO: SPI master-in/slave-out. When configured as master, this pin is an input. When
configured as slave, this pin is an output.
MOSI: SPI master-out/slave-in (Remap mode). When configured as master, this pin is an output.
When configured as slave, this pin is an input. During In-System Programming, this pin is an
input.
CEX2: Capture/Compare external I/O for PCA module 2.
P1.6: User-configurable I/O Port 1 bit 6.
SCK: SPI Clock. When configured as master, this pin is an output. When configured as slave,
this pin is an input.
MISO: SPI master-in/slave-out (Remap mode). When configured as master, this pin is an input.
When configured as slave, this pin is an output. During In-System Programming, this pin is an
output.
CEX3: Capture/Compare external I/O for PCA module 3.
P1.7: User-configurable I/O Port 1 bit 7.
MOSI: SPI master-out/slave-in. When configured as master, this pin is an output. When
configured as slave, this pin is an input.
SCK: SPI Clock (Remap mode). When configured as master, this pin is an output. When
configured as slave, this pin is an input. During In-System Programming, this pin is an input.
CEX4: Capture/Compare external I/O for PCA module 4.
RST: External Reset input (Reset polarity depends on POL pin. See “External Reset” on page
57.). The RST pin can output a pulse when the internal Watchdog reset or POR is active.
DCL: Serial Debug Clock input for On-Chip Debug Interface when OCD is enabled.
P3.0
I/O
I
P3.0: User-configurable I/O Port 3 bit 0.
RXD: Serial Port Receiver Input.
P4.1
I/O
I/O
P4.1: User-configurable I/O Port 4bit 1.
SDA: TWI bidirectional Serial Data line.
11
P3.1
I/O
O
P3.1: User-configurable I/O Port 3 bit 1.
TXD: Serial Port Transmitter Output.
14
12
P3.2
I/O
I
P3.2: User-configurable I/O Port 3 bit 2.
INT0: External Interrupt 0 Input or Timer 0 Gate Input.
9
15
13
P3.3
I/O
I
P3.3: User-configurable I/O Port 3 bit 3.
INT1: External Interrupt 1 Input or Timer 1 Gate Input
10
16
14
P3.4
I/O
I/O
P3.4: User-configurable I/O Port 3 bit 4.
T1: Timer/Counter 0 External input or output.
11
17
15
P3.5
I/O
I/O
P3.5: User-configurable I/O Port 3 bit 5.
T1: Timer/Counter 1 External input or output.
12
18
16
P3.6
I/O
O
P3.6: User-configurable I/O Port 3 bit 6.
WR: External memory interface Write Strobe (active-low).
13
19
17
P3.7
I/O
O
P3.7: User-configurable I/O Port 3 bit 7.
RD: External memory interface Read Strobe (active-low).
14
20
18
P4.7
I/O
O
P4.7: User-configurable I/O Port 4 bit 7.
XTAL2A: Output from inverting oscillator amplifier A. It may be used as a port pin if the internal
RC oscillator or external clock is selected as the clock source A.
15
21
19
P4.6
I/O
I
P4.6: User-configurable I/O Port 4 bit 6.
XTAL1A: Input to the inverting oscillator amplifier A and internal clock generation circuits. It may
be used as a port pin if the internal RC oscillator is selected as the clock source A.
5
11
6
12
7
13
8
10
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 1-1.
Atmel AT89LP51RD2-ED2-ID2 Pin Description (Continued)
Pin Number
(1)
VQFP
VQFN
PLCC
PDIP
Symbol
Type
16
22
20
GND
I
17
23
P4.3
I/O
I/O
P4.3: User-configurable I/O Port 4bit 3.
DDA: Bidirectional Debug Data line for the On-Chip Debug Interface when OCD is enabled.
18
24
21
P2.0
I/O
O
P2.0: User-configurable I/O Port 2 bit 0.
A8: External memory interface Address bit 8.
19
25
22
P2.1
I/O
O
P2.1: User-configurable I/O Port 2 bit 1.
A9: External memory interface Address bit 9.
20
26
23
P2.1
I/O
O
O
P2.2: User-configurable I/O Port 2 bit 2.
DA-: DAC negative differential output.
A10: External memory interface Address bit 10.
21
27
24
P2.3
I/O
O
O
P2.3: User-configurable I/O Port 2 bit 3.
DA+-: DAC positive differential output.
A11: External memory interface Address bit 11.
22
28
25
P2.4
I/O
I
O
P2.4: User-configurable I/O Port 2 bit 5.
AIN0: Analog Comparator Input 0.
A12: External memory interface Address bit 12.
23
29
26
P2.5
I/O
I
O
P2.5: User-configurable I/O Port 2 bit 5.
AIN1: Analog Comparator Input 1.
A13: External memory interface Address bit 13.
24
30
27
P2.6
I/O
I
O
P2.6: User-configurable I/O Port 2 bit 6.
AIN2: Analog Comparator Input 2.
A14: External memory interface Address bit 14.
25
31
28
P2.7
I/O
I
O
P2.7: User-configurable I/O Port 2 bit 7.
AIN3: Analog Comparator Input 3.
A15: External memory interface Address bit 15.
26
32
29
P4.5
I/O
O
P4.5: User-configurable I/O Port 4 bit 5.
PSEN: External memory interface Program Store Enable (active-low).
27
33
30
P4.4
I/O
I/O
P4.4: User-configurable I/O Port 4 bit 4.
ALE: External memory interface Address Latch Enable.
28
34
P4.0
I/O
P4.0: User-configurable I/O Port 4 bit 0.
SCL: TWI Serial Clock line. This line is an output in mater mode and an input in slave mode.
29
35
31
POL
I
30
36
32
P0.7
I/O
I/O
P0.7: User-configurable I/O Port 0 bit 7.
AD7: External memory interface Address/Data bit 7.
31
37
33
P0.6
I/O
I/O
I
P0.6: User-configurable I/O Port 0 bit 6.
AD6: External memory interface Address/Data bit 6.
ADC6: ADC analog input 6.
32
38
34
P0.5
I/O
I/O
I
P0.5: User-configurable I/O Port 0 bit 5.
AD5: External memory interface Address/Data bit 5.
ADC5: ADC analog input 5.
33
39
35
P0.4
I/O
I/O
I
P0.4: User-configurable I/O Port 0 bit 4.
AD4: External memory interface Address/Data bit 4.
ADC4: ADC analog input 4.
34
40
36
P0.3
I/O
I/O
I
P0.3: User-configurable I/O Port 0 bit 3.
AD3: External memory interface Address/Data bit 3.
ADC3: ADC analog input 3.
Description
Ground
POL: Reset polarity (See “External Reset” on page 57.)
5
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 1-1.
Atmel AT89LP51RD2-ED2-ID2 Pin Description (Continued)
Pin Number
(1)
VQFP
VQFN
PLCC
PDIP
Symbol
Type
35
41
37
P0.2
I/O
I/O
I
P0.2: User-configurable I/O Port 0 bit 2.
AD2: External memory interface Address/Data bit 2.
ADC2: ADC analog input 2.
36
42
38
P0.1
I/O
I/O
I
P0.1: User-configurable I/O Port 0 bit 1.
AD1: External memory interface Address/Data bit 1.
ADC1: ADC analog input 1.
37
43
39
P0.0
I/O
I/O
I
P0.0: User-configurable I/O Port 0 bit 0.
AD0: External memory interface Address/Data bit 0.
ADC0: ADC analog input 0.
38
44
40
VDD
I
39
1
P4.2
Description
Supply Voltage
I/O
O
P4.2: User-configurable I/O Port 4bit 2.
XTAL2B: Output from low-frequency inverting oscillator amplifier B (AT89LP51ID2 only). It may
be used as a port pin if the internal RC oscillator or external clock is selected as the clock source
B.
I/O
I/O
I
P1.0: User-configurable I/O Port 1 bit 0.
T2: Timer 2 External Input or Clock Output.
XTAL1B: Input to the low-frequency inverting oscillator amplifier B and internal clock generation
circuits. It may be used as a port pin if the internal RC oscillator is selected as the clock source
B.
40
2
1
P1.0
41
3
2
P1.1
I/O
I
I
P1.1: User-configurable I/O Port 1 bit 1.
T2EX: Timer 2 External Capture/Reload Input.
SS: SPI Slave-Select.
42
4
3
P1.2
I/O
P1.2: User-configurable I/O Port 1 bit 2.
43
5
4
P1.3
I/O
I/O
P1.3: User-configurable I/O Port 1 bit 3.
CEX0: Capture/Compare external I/O for PCA module 0.
44
6
5
P1.4
I/O
I
I/O
P1.4: User-configurable I/O Port 1 bit 4.
SS: SPI Slave-Select (Remap Mode). This pin is an input for In-System Programming
CEX1: Capture/Compare external I/O for PCA module 1.
Note:
1. The AT89LP51ID2 is not available in the PDIP package
2. Overview
The Atmel® AT89LP51RD2-ED2-ID2 is a low-power, high-performance CMOS 8-bit 8051 microcontroller with 64KB of In-System Programmable Flash program memory. The AT89LP51ED2
and AT89LP51ID2 provide an additional 4KB of EEPROM for nonvolatile data storage. The
devices are manufactured using Atmel's high-density nonvolatile memory technology and are
compatible with the industry-standard 80C51 instruction set.
The AT89LP51RD2-ED2-ID2 is built around an enhanced CPU core that can fetch a single byte
from memory every clock cycle. In the classic 8051 architecture, each fetch requires 6 clock
cycles, forcing instructions to execute in 12, 24 or 48 clock cycles. In the AT89LP51RD2-ED2ID2 CPU, standard instructions need only one to four clock cycles providing six to twelve times
more throughput than the standard 8051. Seventy percent of instructions need only as many
clock cycles as they have bytes to execute, and most of the remaining instructions require only
one additional clock. The enhanced CPU core is capable of 20 MIPS throughput whereas the
classic 8051 CPU can deliver only 4 MIPS at the same current consumption. Conversely, at the
same throughput as the classic 8051, the new CPU core runs at a much lower speed and
thereby greatly reducing power consumption and EMI. The AT89LP51RD2-ED2-ID2 also
6
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
includes a compatibility mode that will enable classic 12 clock per machine cycle operation for
true timing compatibility with the Atmel AT89C51RD2/ED2.
The AT89LP51RD2-ED2-ID2 retains all of the standard features of the AT89C51RD2/ED2,
including: 64KB of In-System Programmable Flash program memory, 4KB of EEPROM
(AT89LP51ED2/ID2 Only), 256 bytes of RAM, 2KB of expanded RAM, up to 40 I/O lines, three
16-bit timer/counters, a Programmable Counter Array, a programmable hardware watchdog
timer, a keyboard interface, a full-duplex enhanced serial port, a serial peripheral interface (SPI),
on-chip crystal oscillator, and a four-level, ten-vector interrupt system. A block diagram is shown
in Figure 2-1.
In addition, the Atmel® AT89LP51RD2-ED2-ID2 provides a Two-Wire Interface (TWI) for up to
400KB/s serial transfer; a 10-bit, 8-channel Analog-to-Digital Converter (ADC) with temperature
sensor and digital-to-analog (DAC) mode; two analog comparators; an 8MHz internal oscillator;
and more on-chip data memory than the Atmel AT89C51RD2/ED2 (4KB vs. 2KB EEPROM and
2048 vs. 1792 bytes ERAM).
Some standard features on the AT89LP51RD2-ED2-ID2 are enhanced with new modes or operations. Mode 0 of Timer 0 or Timer 1 acts as a variable 9–16 bit timer/counter and Mode 1 acts
as a 16-bit auto-reload timer/counter. In addition, each timer/counter may independently drive an
8-bit precision pulse width modulation output. Mode 0 (synchronous mode) of the serial port
allows flexibility in the phase/polarity relationship between clock and data.
The I/O ports of the AT89LP51RD2-ED2-ID2 can be independently configured in one of four
operating modes. In quasi-bidirectional mode, the ports operate as in the classic 8051. In inputonly mode, the ports are tristated. Push-pull output mode provides full CMOS drivers and opendrain mode provides just a pull-down. Unlike other 8051s, this allows Port 0 to operate with onchip pull-ups if desired.
The AT89LP51RD2-ED2-ID2 includes an On-Chip Debug (OCD) interface that allows readmodify-write capabilities of the system state and program flow control, and programming of the
internal memories. The on-chip Flash and EEPROM may also be programmed through the
UART-based bootloader or the SPI-based In-System programming interface (ISP).
The TWI and OCD features are not available on the PDIP package. The AT89LP51ID2 is also
not available in the PDIP.
The features of the AT89LP51RD2-ED2-ID2 make it a powerful choice for applications that need
pulse width modulation, high speed I/O, and counting capabilities such as alarms, motor control,
corded phones, and smart card readers.
7
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
2.1
Block Diagram
Figure 2-1.
Atmel AT89LP51RD2-ED2-ID2 Block Diagram
Flash Code
64KB
Boot ROM
2KB
EEPROM
4KB
RAM
256 Bytes
ERAM
2KB
XRAM
Interface
(AT89LP51ED2/ID2)
8051 Single Cycle CPU
with 12-cycle Compatiblity
Port 0
Configurable I/O
Port 1
Configurable I/O
UART
Watchdog
Timer
SPI
Keyboard
Interface
Port 2
Configurable I/O
Dual Data
Pointers
Port 3
Configurable I/O
Multiply
Accumulate
(16 x 16)
Port 4
Configurable I/O
Timer 0
Timer 1
Timer 2
PCA
POR
BOD
Dual Analog
Comparators
2.2
Crystal or
Resonator
Configurable
Oscillator A
Crystal or
Resonator
Configurable
Oscillator B
7
Internal 8 MHz
RC Oscillator
10-bit
ADC/DAC
TWI
On-Chip
Debug
(AT89LP51ID2)
System Configuration
The AT89LP51RD2-ED2-ID2 supports several system configuration options. Nonvolatile options
are set through user fuses that must be programmed through the flash programming interface.
Volatile options are controlled by software through individual bits of special function registers
(SFRs). The AT89LP51RD2-ED2-ID2 must be properly configured before correct operation can
occur.
2.2.1
Fuse Options
Table 2-1 lists the fusible options for the AT89LP51RD2-ED2-ID2. These options maintain their
state even when the device is powered off. Some may be changed through the Flash API but
others can only be changed with an external device programmer. For more information, see
Section 23.2 “User Configuration Fuses” on page 192.
8
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 2-1.
2.2.2
User Configuration Fuses
Fuse Name
Description
Clock Source A
Selects between the High Speed Crystal Oscillator, Low Power
Crystal Oscillator, External Clock on XTAL1A or Internal RC Oscillator
for the source of the system clock when oscillator A is selected.
Clock Source B
Selects between the 32 kHzCrystal Oscillator, External Clock on
XTAL1B or Internal RC Oscillator for the source of the system clock
when oscillator B is selected (AT89LP51ID2 Only).
Oscillator Select
Selects whether oscillator A or B is enabled to boot the device.
(AT89LP51ID2 Only)
X2 Mode
Selects the default state of whether the clock source is divided by two
(X1) or not (X2) to generate the system clock.
Start-up Time
Selects time-out delay for the POR/BOD/PWD wake-up period.
Compatibility Mode
Configures the CPU in 12-clock compatibility or single-cycle fast
execution mode.
XRAM Configuration
Configures if access to on-chip memories that are mapped to the
external data memory address space is enabled/disabled by default.
Bootloader Jump Bit
Enables or disables the on-ship bootloader.
On-Chip Debug Enable
Enables or disables On-Chip Debug. OCD must be enabled prior to
using an in-circuit debugger with the device.
In-System Programming Enable
Enables or disables In-System Programming.
User Signature Programming Enable
Enables or disables programming of User Signature array.
Default Port State
Configures the default port state as input-only mode (tristated) or
quasi-bidirectional mode (weakly pulled high).
Low Power Mode
Enables or disables power reduction features for lower system
frequencies.
Software Options
Table 2-2 lists some important software configuration bits that affect operation at the system
level. These can be changed by the application software but are set to their default values upon
any reset. Most peripherals also have multiple configuration bits that are not listed here.
Table 2-2.
Important Software Configuration Bits
Bit(s)
SFR Location
Description
PxM0.y
PxM1.y
P0M0, P0M1, P1M0, P1M1,
P2M0, P2M1, P3M0, P3M1,
P4M0, P4M1
Configures the I/O mode of Port x Pin y to be one of input-only, quasibidirectional, push-pull output or open-drain. The default state is
controlled by the Default Port State fuse above
CKRL
CKRL
Selects the division ratio between the oscillator and the system clock
X2
CKCON0
Selects the division ratio between the oscillator and the system clock
TPS3-0
CLKREG.7-4
Selects the division ratio between the system clock and the timers
AO
AUXR.0
Enables/disables toggling of ALE
EXRAM
AUXR.1
Enables/disables access to on-chip memories that are mapped to the
external data memory address space
WS1-0
AUXR.6-5
Selects the number of wait states when accessing external data
memory
XSTK
AUXR1.4
Configures the hardware stack to be in RAM or extra RAM
EEE
EECON.1
Enables/disables access to the on-chip EEPROM
ENBOOT
AUXR1.5
Enables/disables access to the on-chip Flash API
9
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
2.3
Comparison to the Atmel AT89C51RD2/ED2/ID2
The Atmel® AT89LP51RD2-ED2-ID2 is part of a family of devices with enhanced features that
are fully binary compatible with the 8051 instruction set. The AT89LP51RD2-ED2-ID2 has two
modes of operations, Compatibility mode and Fast mode. In Compatibility mode the instruction
timing, peripheral behavior, SFR addresses, bit assignments and pin functions are identical to
the existing Atmel AT89C51RD2/ED2/ID2 product. Additional enhancements are transparent to
the user and can be used if desired. Fast mode allows greater performance, but with some differences in behavior. The major enhancements from the AT89C51RD2/ED2/ID2 are outlined in
the following paragraphs and may be useful to users migrating to the AT89LP51RD2-ED2-ID2
from older devices. A summary of the differences between Compatibility and Fast modes is
given in Table 2-3 on page 10. See also the Application note “Migrating from
AT89C51RD2/ED2/ID2 to AT89LP51RD2-ED2-ID2.”
2.3.1
Instruction Execution
In Compatibility mode the Atmel® AT89LP51RD2-ED2-ID2 CPU uses the six-state machine
cycle of the standard 8051 where instruction bytes are fetched every three system clock cycles.
Execution times in this mode are identical to the Atmel AT89C51RD2/ED2/ID2. For greater performance the user can enable Fast mode by disabling the Compatibility fuse. In Fast mode the
CPU fetches one code byte from memory every clock cycle instead of every three clock cycles.
This greatly increases the throughput of the CPU. Each standard instruction executes in only
one to four clock cycles. See “Instruction Set Summary” on page 177 for more details. Any software delay loops or instruction-based timing operations may need to be retuned to achieve the
desired results in Fast mode.
Table 2-3.
Compatibility Mode versus Fast Mode Summary
Feature
Compatibility
Fast
3
1
6, 12, 18 or 24
1, 2, 3, 4 or 5
Default System Clock Divisor
2
1
Default Timer Prescaler Divisor
6
1
Prescaler Rate
System Clock
12
2
Instruction Fetch in System Clocks
Instruction Execution Time in System Clocks
Pin Sampling Rate (INT0, INT1, T0, T1, T2, T2EX)
Minimum RST input pulse in System Clocks
2.3.2
System Clock
The system clock source is not limited to a crystal or external clock. The system clock source is
selectable between the crystal oscillator, an externally driven clock and an internal 8.0MHz RC
oscillator for AT89LP51RD2/ED2 and clock source A of AT89LP51ID2. Clock source B of
AT89LP51ID2 is not limited to a 32 kHz crystal. The clock source B is selectable between the 32
kHz crystal oscillator, an externally driven clock and an internal 8.0MHz RC oscillator. Unlike
AT89C51ID2, the X2 and CKRL features will also affect the OSCB source.
By default in Compatibility mode the system clock frequency is divided by 2 from the externally
supplied XTAL1 frequency for compatibility with standard 8051s (12 clocks per machine cycle).
The System Clock Divider can scale the system clock versus the oscillator source (See Section
6.8 on page 51). The divide-by-2 can be disabled to operate in X2 mode (6 clocks per machine
cycle) or the clock may be further divided to reduce the operating frequency. In Fast mode the
clock divider defaults to divide by 1.
10
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
2.3.3
Reset
The RST pin of the AT89LP51RD2-ED2-ID2 has selectable polarity using the POL pin (formerly
EA). When POL is high the RST pin is active high with a pull-down resistor and when POL is low
the RST pin is active low with a pull-up resistor. For existing AT89C51RD2/ED2/ID2 sockets
where EA is tied to VDD, replacing AT89C51RD2/ED2 with AT89LP51RD2-ED2-ID2 will maintain the active high reset. Note that forcing external execution by tying EA low is not supported.
The AT89LP51RD2-ED2-ID2 includes an on-chip Power-On Reset and Brown-out Detector circuit that ensures that the device is reset from system power up. In most cases a RC startup
circuit is not required on the RST pin, reducing system cost, and the RST pin may be left unconnected if a board-level reset is not present.
2.3.4
Timer/Counters
A common prescaler is available to divide the time base for Timer 0, Timer 1, Timer 2 and the
WDT. The TPS3-0 bits in the CLKREG SFR control the prescaler (Table 6-8 on page 51). In
Compatibility mode TPS3-0 defaults to 0101B, which causes the timers to count once every
machine cycle. The counting rate can be adjusted linearly from the system clock rate to 1/16 of
the system clock rate by changing TPS3-0. In Fast mode TPS3-0 defaults to 0000B, or the system
clock rate. TPS does not affect Timer 2 in Clock Out or Baud Generator modes.
In Compatibility mode the sampling of the external Timer/Counter pins: T0, T1, T2 and T2EX;
and the external interrupt pins, INT0 and INT1, is also controlled by the prescaler. In Fast mode
these pins are always sampled at the system clock rate.
Both Timer 0 and Timer 1 can toggle their respective counter pins, T0 and T1, when they overflow by setting the output enable bits in TCONB.
2.3.5
Interrupt Handling
Fast mode allows for faster interrupt response due to the shorter instruction execution times.
2.3.6
Keyboard Interface
The AT89LP51RD2-ED2-ID2 does not clear the keyboard flag register (KBF) after a read. Each
bit must be cleared in software. This allows the interrupt to be generate once per flag when multiple flags are set, if desired. To mimic the old behavior the service routine must clear the whole
register.
The keyboard can also support general edge-triggered interrupts with the addition of the
KBMOD register.
2.3.7
Serial Port
The timer prescaler increases the range of achievable baud rates when using Timer 1 to generate the baud rate in UART Modes 1 or 3, including an increase in the maximum baud rate
available in Compatibility mode. Additional features include automatic address recognition and
framing error detection.
The shift register mode (Mode 0) has been enhanced with more control of the polarity, phase
and frequency of the clock and full-duplex operation. This allows emulation of master serial
peripheral (SPI) and two-wire (TWI) interfaces.
11
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
2.3.8
I/O Ports
The P0, P1, P2 and P3 I/O ports of the AT89LP51RD2-ED2-ID2 may be configured in four different modes. The default setting depends on the Tristate-Port User Fuse. When the fuse is set all
the I/O ports revert to input-only (tristated) mode at power-up or reset. When the fuse is not
active, ports P1, P2 and P3 start in quasi-bidirectional mode and P0 starts in open-drain mode.
P4 always operates in quasi-bidirectional mode. P0 can be configured to have internal pull-ups
by placing it in quasi-bidirectional or output modes. This can reduce system cost by removing
the need for external pull-ups on Port 0.
The P4.4–P4.7 pins are additional I/Os that replace the normally dedicated ALE, PSEN, XTAL1
and XTAL2 pins of the AT89C51RD2/ED2/ID2. These pins can be used as additional I/Os
depending on the configuration of the clock and external memory.
2.3.9
Security
The AT89LP51RD2-ED2-ID2 does not support the external access pin (EA). Therefore it is not
possible to execute from external program memory in address range 0000H–1FFFH. When the
third Lockbit is enabled (Lock Mode 4) external program execution is disabled for all addresses
above 1FFFH. This differs from AT89C51RD2/ED2/ID2 where Lock Mode 4 prevents EA from
being sampled low, but may still allow external execution at addresses outside the 8K internal
space.
2.3.10
Programming
The AT89LP51RD2-ED2-ID2 supports the same bootloader protocols as
AT89C51RD2/ED2/ID2. Existing AT89C51RD2/ED2/ID2 bootloader-based programmers should
be able to program the AT89LP51RD2-ED2-ID2, although all features may not be configurable.
AT89LP51RD2-ED2-ID2 does not support parallel programming in the manner of
AT89C51RD2/ED2/ID2. Stand-alone programmers will need to be updated with a new driver for
AT89LP51RD2-ED2-ID2 that supports the SPI-based programming interface.
12
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
3. Memory Organization
The AT89LP51RD2/ED2/ID2 uses a Harvard Architecture with separate address spaces for program and data memory. The program memory has a regular linear address space with support
for 64K bytes of directly addressable application code. The data memory has 256 bytes of internal RAM and 128 bytes of Special Function Register I/O space. The AT89LP51RD2/ED2/ID2
supports up to 64K bytes of external data memory, with portions of the external data memory
space implemented on chip as nonvolatile Flash data memory. External program memory is
supported for addresses above 32K in some configurations. The memory address spaces of the
AT89LP51RD2/ED2/ID2 are listed in Table 3-1.
Table 3-1.
Name
Description
DATA
Directly addressable internal RAM
00H–7FH
IDATA
Indirectly addressable internal RAM and stack space
00H–FFH
SFR
Directly addressable I/O register space
80H–FFH
EDATA
On-chip Extra RAM and extended stack space
FDATA
On-chip nonvolatile EEPROM data memory
(AT89LP51ED2 and AT89LP51ID2 only)
0000H–0FFFH
XDATA
External data memory
0000H–FFFFH
CODE
On-chip nonvolatile Flash program memory
0000H–FFFFH
XCODE
External program memory
8000H–FFFFH
SIG
On-chip nonvolatile Flash signature array
0000H–01FFH
BOOT
On-chip Bootloader ROM and Flash API
F800H–FFFFH
Note:
3.1
AT89LP51RD2/ED2/ID2 Memory Address Spaces
Range
0000H–07FFH(1)
1. The size of the EDATA space is configurable with the XRS bits in AUXR.
Program Memory
The AT89LP51RD2/ED2/ID2 contains 64K bytes of on-chip In-System Programmable Flash
memory for program storage, plus support for up to 32K bytes of external program memory. The
Flash memory has an endurance of at least 10,000 write/erase cycles and a minimum data
retention time of 10 years. The reset and interrupt vectors are located within the first 83 bytes of
program memory (refer to Table 9-1 on page 63). Constant tables can be allocated within the
entire 64K program memory address space for access by the MOVC instruction. A map of the
AT89LP51RD2/ED2/ID2 program memory is shown in Figure 3-1. See Section 23. “Flash Memory Programming” on page 189 for more information on programming the flash memory.
Table 3-2.
BMSEL – Bank Mode Select Register
BMSEL = 92H
Reset Value = XXXX XXX0B
Not Bit Addressable
Bit
—
—
—
—
—
—
—
FBS
7
6
5
4
3
2
1
0
Symbol
Function
FBS
Fetch Bank Select. When FBS = 0 addresses 8000H–FFFFH are fetched from the internal Flash program memory.
When FBS = 1 addresses 8000H–FFFFH are fetched from the external program memory. FBS can only be modified by
instructions executing internally in the range 0000H–7FFFH.
13
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 3-1.
Program Memory Map
01FF
01FF
01FF
User Signature Array
User Signature Array
01FF
User Signature Array
User Signature Array
0100
0100
0100
0100
007F
007F
007F
007F
Atmel Signature Array
Atmel Signature Array
0000
0000
FFFF
FFFF
F800
F7FF
Boot ROM
Atmel Signature Array
0000
0000
FFFF
FFFF
(BOOT: 2KB)
Internal Program
Memory
(CODE: 62KB)
Internal Program
Memory
(CODE: 64KB)
Atmel Signature Array
External Program
Memory
(XCODE: 32KB)
8000
7FFF
F800
F7FF
8000
7FFF
Internal Program
Memory
(CODE: 32KB)
0000
0000
FBS = 0
ENBOOT = 0
3.1.1
0000
FBS = 0
ENBOOT = 1
SIGEN=1
Boot ROM
(BOOT: 2KB)
External Program
Memory
(XCODE: 30KB)
SIGEN=0
Internal Program
Memory
(CODE: 32KB)
0000
FBS = 1
ENBOOT = 0
FBS = 1
ENBOOT = 1
External Program Memory
The AT89LP51RD2/ED2/ID2 implements the entire 16-bit, 64 KB program memory space internally. The AT89LP51RD2/ED2/ID2 does not support forcing external execution using the EA pin;
however it does include a bank-switching mechanism to allow for up to 32 KB of external program memory to be mapped into the upper half of the address space. The FBS bit in the BMSEL
SFR (Table 3-2) selects whether addresses 8000H–FFFFH are mapped to internal or external
program memory. FBS can only be modified by instructions executing internally in the range
0000H–7FFFH
The AT89LP51RD2/ED2/ID2 uses the standard 8051 external program memory interface with
the upper address on Port 2, the lower address and data in/out multiplexed on Port 0, and the
ALE and PSEN strobes. Program memory addresses are always 16-bits wide. External program
execution sacrifices two full 8-bit ports, P0 and P2, to the function of addressing the program
memory.
Figure 3-2 shows a hardware configuration for accessing up to 64K bytes of external ROM using
a 16-bit linear address. Port 0 serves as a multiplexed address/data bus to the ROM. The
Address Latch Enable strobe (ALE) is used to latch the lower address byte into an external register so that Port 0 can be freed for data input/output. Port 2 provides the upper address byte
throughout the operation. PSEN strobes the external memory.
Figure 3-3 shows the timing of the external program memory interface. ALE is emitted at a constant rate of 1/3 of the system clock with a 1/3 duty cycle. PSEN is emitted at a similar rate, but
with 50% duty cycle. The new address changes in the middle of the ALE pulse for latching on
the falling edge and is tristated at the falling edge of PSEN. The instruction data is sampled from
P0 and latched internally during the high phase of the clock prior to the rising edge of PSEN.
This timing applies to both Compatibility and Fast modes. In Compatibility mode there is no difference in instruction timing between internal and external execution.
14
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 3-2.
Executing from External Program Memory
AT89LP
P1
EXTERNAL
PROGRAM
MEMORY
INSTR.
P0
ALE
LATCH
P3
PSEN
Figure 3-3.
ADDR
P2
OE
External Program Memory Fetches
CLK
ALE
PSEN
DATA
SAMPLED
PCL
OUT
P0
FLOAT
DATA
SAMPLED
DATA
SAMPLED
PCL
OUT
PCL
OUT
PCH OUT
P2
PCH OUT
PCH OUT
In order for Fast mode to fetch externally, two wait states must be inserted for every clock cycle,
increasing the instruction execution time by a factor of 3. However, due to other optimizations,
external Fast mode instructions may still be 1/4 to 1/2 faster than their Compatibility mode equivalents. Note that if ALE is allowed to toggle in Fast mode, there is a possibility that when the
CPU jumps from internal to external execution a short pulse may occur on ALE as shown in Figure 3-4. The setup time from the address to the falling edge of ALE remains the same. However,
this behavior can be avoided by setting the AO bit prior to any jump above the 32K border.
Figure 3-4.
Internal/External Program Memory Boundary (Fast Mode)
CLK
SHORT
PULSE
ALE
AO=0
ALE
AO=1
INTERNAL EXECUTION
EXTERNAL EXECUTION
PSEN
DATA
SAMPLED
P0
P0 SFR OUT
P2
P2 SFR OUT
PCL OUT
FLOAT
PCH OUT
PCL OUT
PCH OUT
15
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
3.1.2
SIG
In addition to the 64K code space, the AT89LP51RD2/ED2/ID2 also supports a 512-byte User
Signature Array and a 128-byte Atmel Signature Array that are accessible by the CPU. The
Atmel Signature Array is initialized with the Device ID in the factory. The User Signature Array is
available for user identification codes or constant parameter data. Data stored in the signature
array is not secure. Security bits will disable writes to the array; however, reads by an external
device programmer are always allowed. The signatures can be accessed with the Flash API
functions or low-level IAP interface. See Section 23.4 “In-Application Programming (IAP)” on
page 194 for more information.
3.2
Internal Data Memory
The AT89LP51RD2/ED2/ID2 contains 256 bytes of general SRAM data memory plus 128 bytes
of I/O memory mapped into a single 8-bit address space. Access to the internal data memory
does not require any configuration. The internal data memory has three address spaces: DATA,
IDATA and SFR; as shown in Figure 3-5. Some portions of external data memory are also implemented internally. See “External Data Memory” below for more information.
Figure 3-5.
Internal Data Memory Map
FFH
FFH
IDATA
ACCESSIBLE
BY INDIRECT
ADDRESSING
ONLY
UPPER
128
80H
7FH
80H
DATA/IDATA
ACCESSIBLE
BY DIRECT
AND INDIRECT
ADDRESSING
LOWER
128
0
3.2.1
SFR
ACCESSIBLE
BY DIRECT
ADDRESSING
SPECIAL
FUNCTION
REGISTERS
PORTS
STATUS AND
CONTROL BITS
TIMERS
REGISTERS
STACK POINTER
ACCUMULATOR
(ETC.)
DATA
The first 128 bytes of RAM are directly addressable by an 8-bit address (00H–7FH) included in
the instruction. The lowest 32 bytes of DATA memory are grouped into 4 banks of 8 registers
each. The RS0 and RS1 bits (PSW.3 and PSW.4) select which register bank is in use. Instructions using register addressing will only access the currently specified bank. The lower 128 bit
addresses are also mapped into DATA addresses 20H—2FH.
3.2.2
IDATA
The full 256 byte internal RAM can be indirectly addressed using the 8-bit pointers R0 and R1.
The first 128 bytes of IDATA include the DATA space. The hardware stack is also located in the
IDATA space.
3.2.3
SFR
The upper 128 direct addresses (80H–FFH) access the I/O registers. I/O registers on AT89LP
devices are referred to as Special Function Registers. The SFRs can only be accessed through
direct addressing. All SFR locations are not implemented. See Section 4. for a listed of available
SFRs.
16
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
3.3
External Data Memory
AT89LP microcontrollers support a 16-bit external memory address space for up to 64K bytes of
external data memory (XDATA). The external memory space is accessed with the MOVX
instructions. Some internal data memory resources are mapped into portions of the external
address space as shown in Figure 3-6. These memory spaces may require configuration before
the CPU can access them. The AT89LP51RD2/ED2/ID2 includes 2K bytes of on-chip Extra
RAM (EDATA) and 4K bytes of nonvolatile EEPROM data memory (FDATA).
3.3.1
XDATA
The external data memory space can accommodate up to 64KB of external memory. The
AT89LP51RD2/ED2/ID2 uses the standard 8051 external data memory interface with the upper
address byte on Port 2, the lower address byte and data in/out multiplexed on Port 0, and the
ALE, RD and WR strobes. XDATA can be accessed with both 16-bit (MOVX @DPTR) and 8-bit
(MOVX @Ri) addresses. See Section 3.3.2 on page 17 for more details of the external memory
interface.
Some internal data memory spaces are mapped into portions of the XDATA address space. In
this case the lower address ranges will access internal resources instead of external memory.
Addresses above the range implemented internally will default to XDATA. The
AT89LP51RD2/ED2/ID2 supports up to 60–62K bytes of external memory when using the internally mapped memories. Setting the EXTRAM bit (AUXR.1) to one will force all MOVX
instructions to access the entire 64KB XDATA regardless of their address (See “AUXR – Auxiliary Control Register” on page 19).
Figure 3-6.
External Data Memory Map
FFFF
FFFF
External Data
(XDATA: 64KB)
FFFF
External Data
(XDATA: 62KB)
0800
07FF
Extra RAM
(EDATA: 2KB)
FFFF
External Data
(XDATA: 62KB)
0800
07FF
Flash Program
(CODE: 64KB)
EEPROM
(FDATA: 2KB)
0000
EXRAM = 1
3.3.2
EXRAM = 0
DMEN = 0
IAP = 0
EXRAM = 0
DMEN = 1
IAP = 0
EXRAM = 0
DMEN = x
IAP = 1
External Data Memory Interface
The AT89LP51RD2/ED2/ID2 uses the standard 8051 external data memory interface with the
upper address on Port 2, the lower address and data in/out multiplexed on Port 0, and the ALE,
RD and WR strobes. The interface may be used in two different configurations depending on
which type of MOVX instruction is used to access XDATA.
17
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 3-7 shows a hardware configuration for accessing up to 64K bytes of external RAM using
a 16-bit linear address. Port 0 serves as a multiplexed address/data bus to the RAM. The
Address Latch Enable strobe (ALE) is used to latch the lower address byte into an external register so that Port 0 can be freed for data input/output. Port 2 provides the upper address byte
throughout the operation. The MOVX @DPTR instructions use Linear Address mode.
Figure 3-7.
External Data Memory 16-bit Linear Address Mode
EXTERNAL
DATA
MEMORY
DATA
AT89LP
P0
P1
ALE
LATCH
ADDR
P2
RD
WR
P3
WE
OE
Figure 3-8 shows a hardware configuration for accessing 256-byte blocks of external RAM using
an 8-bit paged address. Port 0 serves as a multiplexed address/data bus to the RAM. The ALE
strobe is used to latch the address byte into an external register so that Port 0 can be freed for
data input/output. The Port 2 I/O lines (or other ports) can provide control lines to page the memory; however, this operation is not handled automatically by hardware. The software application
must change the Port 2 register when appropriate to access different pages. The MOVX @Ri
instructions use Paged Address mode.
Figure 3-8.
External Data Memory 8-bit Paged Address Mode
EXTERNAL
DATA
MEMORY
DATA
AT89LP
P1
P0
ALE
RD
WR
LATCH
ADDR
PAGE
BITS
WE
P3 P2
I/O
OE
Note that prior to using the external memory interface, WR (P3.6) and RD (P3.7) must be configured as outputs. See Section 11.2 “Port Configuration” on page 73. P0 and P2 are configured
automatically to push-pull output mode when outputting address or data and P0 is automatically
tristated when inputting data regardless of the port configuration. The Port 0 configuration will
determine the idle state of Port 0 when not accessing the external memory.
Figure 3-9 and Figure 3-10 show examples of external data memory write and read cycles,
respectively. The address on P0 and P2 is stable at the falling edge of ALE. The idle state of
ALE is controlled by AO (AUXR.0). When AO = 0 the ALE toggles at a constant rate when not
accessing external memory. When AO = 1 the ALE is weakly pulled high. DISALE must be one
in order to use P4.4 as a general-purpose I/O. The WS bits in AUXR can extended the RD and
WR strobes by 1, 2 or 3 cycles as shown in Figures 3-13, 3-14 and 3-15. If a longer strobe is
18
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
required, the application can scale the system clock with the clock divider to meet the requirements (See Section 6.8 on page 51).
Table 3-3.
AUXR – Auxiliary Control Register
AUXR = 8EH
Reset Value = 0000 10X0B
Not Bit Addressable
DPU
WS1(1)
WS0
XRS2
XRS1
XRS0
EXTRAM
AO
7
6
5
4
3
2
1
0
Bit
Symbol
Function
DPU
Disable Weak Pull-up. When DPU = 0 all I/O ports in quasi-bidirectional mode have their weak pull-up enabled. When
DPU = 1 all I/O ports in quasi-bidirectional mode have their weak pull-up disabled to reduce power consumption.
WS1-0
Wait State Select. Determines the number of wait states inserted into external memory accesses.
WS1
WS0
Wait States
RD / WR Strobe Width
ALE to RD / WR Setup
0
0
0
1 x tCYC (Fast); 3 x tCYC (Compatibility)
1 x tCYC (Fast); 1.5 x tCYC (Compatibility)
0
1
1
2 x tCYC (Fast); 15 x tCYC (Compatibility)
1 x tCYC (Fast); 1.5 x tCYC (Compatibility)
1
0
2
2 x tCYC (Fast)
2 x tCYC (Fast)
1
1
3
3 x tCYC (Fast)
2 x tCYC (Fast)
XRAM Size. Selects the size of the on-chip extra RAM (EDATA)
XRS2-0
XRS2
XRS1
XRS0
EDATA Size (bytes)
Address Range
0
0
0
256
0000H–00FFH
0
0
1
512
0000H–01FFH
0
1
0
768 (default)
0000H–02FFH
0
1
1
1024
0000H–03FFH
1
0
0
1792
0000H–06FFH
1
0
1
2048
0000H–07FFH
1
1
–
Reserved
EXTRAM
External RAM Enable. When EXTRAM = 0, MOVX instructions can access the internally mapped portions of the
address space (Extra RAM and EEPROM). Accesses to addresses above internally mapped memory will access
external memory. Set EXTRAM = 1 to bypass the internal memory and map the entire 64KB address space to external
memory. The default state of EXTRAM is set by a user configuration fuse. See Section 23.2 on page 192.
AO
ALE Output. When AO = 0 the ALE pulse is active at 1/3 of the system clock frequency in Compatibility mode and 1/2 of
the system clock frequency in Fast mode. When AO = 1 the ALE is inactive (high) unless an external memory access
occurs. AO must be set to use P4.4 as a general I/O.
Notes:
1. WS1 is only available in Fast mode. WS1 is forced to 0 in Compatibility mode.
19
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 3-9.
Fast Mode External Data Memory Write Cycle (WS = 00B)
S1
S2
S3
P0
P0 SFR
DPL or Ri OUT
P2
P2 SFR
S4
CLK
ALE
WR
Figure 3-10.
DATA OUT
P0 SFR
DPH or P2 OUT
P2 SFR
Fast Mode External Data Memory Read Cycle (WS = 00B)
S1
S2
S3
P0
P0 SFR
DPL or Ri OUT
P2
P2 SFR
S4
CLK
ALE
RD
DATA SAMPLED
P0 SFR
FLOAT
DPH or P2 OUT
P2 SFR
Figure 3-11. Compatibility Mode External Data Memory Write Cycle (WS0 = 0)
S4
S5
S6
S1
S2
S3
S4
S5
CLK
ALE
WR
20
P0
P0 SFR
P2
PCH or
P2 SFR
DPL or Ri
OUT
DATA OUT
DPH or P2 OUT
PCL or
P0 SFR
PCH or
P2 SFR
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 3-12. Compatibility Mode External Data Memory Read Cycle (WS0 = 0)
S4
S5
S6
S1
S2
S3
S4
S5
CLK
ALE
RD
DATA SAMPLED
P0
P0 SFR
P2
PCH or
P2 SFR
DPL or Ri
OUT
PCL or
P0 SFR
FLOAT
PCH or
P2 SFR
DPH or P2 OUT
Figure 3-13. MOVX with One Wait State (WS = 01B)
S1
S2
S3
W1
S4
CLK
ALE
P2
P2 SFR
DPH or P2 OUT
P2 SFR
WR
P0
P0 SFR
DPL OUT
P0 SFR
DPL OUT
DATA OUT
P0 SFR
RD
P0
FLOAT
P0 SFR
Figure 3-14. MOVX with Two Wait States (WS = 10B)
S1
S2
S3
W1
W2
S4
CLK
ALE
P2
P2 SFR
DPH or P2 OUT
P2 SFR
WR
P0
P0 SFR
DPL OUT
P0 SFR
DPL OUT
DATA OUT
P0 SFR
RD
P0
FLOAT
P0 SFR
21
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 3-15. MOVX with Three Wait States (WS = 11B)
S1
S2
S3
W1
W2
W3
S4
CLK
ALE
P2
P2 SFR
DPH or P2 OUT
P2 SFR
WR
P0
P0 SFR
DPL OUT
P0 SFR
DPL OUT
DATA OUT
P0 SFR
RD
P0
3.4
FLOAT
P0 SFR
Extra RAM (EDATA)
The Extra RAM is a portion of the external memory space implemented as an internal 2K byte
auxiliary RAM. The Extra RAM is mapped into the EDATA space at the bottom of the external
memory address space, from 0000H to 07FFH, when EXTRAM = 0 (AUXR.1). The size of
EDATA can be reduced by the XRS bits in AUXR (See Table 3-3). MOVX instructions to this
address range will access the internal Extra RAM. EDATA can be accessed with both 16-bit
(MOVX @DPTR) and 8-bit (MOVX @Ri) addresses. When 8-bit addresses are used, the PAGE
register (0F6H) supplies the upper address bits. The PAGE register breaks EDATA into eight
256-byte pages. A page cannot be specified independently for MOVX @R0 and MOVX @R1.
Setting PAGE above 07H enables XDATA access, but does not change the value of Port 2.
When 16-bit addresses are used (DPTR), the EEE bit (EECON.1) must also be zero to access
EDATA. MOVX instructions to EDATA require a minimum of 2 clock cycles.
Table 3-4.
PAGE – EDATA Page Register
PAGE = F6H
Reset Value = 0000 0000B
Not Bit Addressable
Bit
—
—
—
—
PAGE.3
PAGE.2
PAGE.1
PAGE.0
7
6
5
4
3
2
1
0
Symbol
Function
PAGE7-0
Selects which 256-byte page of EDATA is currently accessible by MOVX @Ri instructions when PAGE < 08H. Any PAGE
value between 08H and FFH will select XDATA; however, this value will not be output on P2.
3.5
EEPROM
The EEPROM is a portion of the external data memory space implemented as an on-chip nonvolatile data memory. EEPROM is enabled by setting the EEE bit (EEMCON.1) to one. When
EXTRAM = 0 and EE = 1, the EEPROM is mapped into the FDATA space, at the bottom of the
external memory address space, from 0000H to 0FFFH. (See Figure 3-6). MOVX instructions to
this address range will access the EEPROM. EEPROM is not accessible while EEE = 0.
EEPROM can be accessed only by 16-bit (MOVX @DPTR) addresses. MOVX @Ri instructions
to the EEPROM address range will access data memory in the EDATA or XDATA spaces.
Addresses above the EEPROM range are mapped to external data memory (XDATA).
This feature is only available on AT89LP51ED2 and AT89LP51ID2.
22
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
3.5.1
Read Protocol
The following procedure is used to read data stored in the on-chip EEPROM.
1. Check EEBUSY flag (EECON.0) and wait for it to go low if necessary
2. Disable interrupts if any interrupt routine accesses external data memory in the range
0000H–0FFFH
3. Set bit EEE in EECON register
4. Load DPTR (or DPTRB) with the address to read
5. Execute MOVX A, @DPTR (or MOVX A, @/DPTR)
6. Repeat steps 4–5 for other locations if needed
7. Clear bit EEE in EECON register
8. Restore interrupts if disabled in #2
3.5.2
Write Protocol
The EEPROM address space accesses an internal nonvolatile data memory. Writes to
EEPROM require a more complex protocol and take several milliseconds to complete. The
AT89LP51RD2/ED2/ID2 uses an execute-while-write architecture where the CPU continues to
operate while the EEPROM write occurs. The software must poll the state of the EEBUSY flag to
determine when the write completes. EEPROM data can be written one byte or one page at a
time.
An EEPROM write includes both an erase and write of the affected byte location. A write
sequence will not occur if the Brown-out Detector was active within the last 2 ms. If a write currently in progress is interrupted by the BOD due to a low voltage condition, the ERR flag
(EECON.2) will be set by hardware.
3.5.2.1
Byte Write
The following procedure is used to write a single byte to the on-chip EEPROM. See Figure 3-16.
1. If the write will occur within 2 ms of a reset or power-up event, check the INHIBIT flag
and wait for it to go high if necessary.
2. Check the EEBUSY flag (EECON.0) and wait for it to go low if necessary
3. Disable interrupts if any interrupt routine accesses external data memory in the range
0000H–0FFFH
4. Set bit EEE in EECON register
5. Load DPTR (or DPTRB) with the address to write
6. Load the accumulator (ACC) with the data to be written
7. Execute MOVX @DPTR, A (or MOVX @/DPTR, A)
8. Clear bit EEE in EECON register
9. Restore interrupts if disabled in #3
10. The EEBUSY flag is set by hardware to indicate that programming is in progress and
that the EEPROM is not available for reading and writing
11. The end of programming is indicated by a hardware clear of EEBUSY
23
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 3-16. EEPROM Byte Write of Two Bytes
EEE
LDPG
EEBUSY
tWC
tWC
MOVX
3.5.2.2
Page Write
The LDPG bit in EECON prevents a write to the EEPROM from starting. While LDPG = 1 all
writes will load the temporary page buffer of the EEPROM. The next write to occur with
LDPG = 0 will write that byte and all previously loaded bytes to the EEPROM. The
AT89LP51ED2/ID2 has a EEPROM buffer of 32 bytes. Address locations that are not loaded will
remain untouched, i.e. no erase/write will occur.
The following procedure is used to write multiple bytes (up to 32) to the on-chip EEPROM. See
Figure 3-17. All bytes must reside within the same 32-byte page boundary and the same byte
may not be loaded more than once. This procedure assumes N bytes will be written, where 2
 N  32.
1. If the write will occur within 2 ms of a reset or power-up event, check the INHIBIT flag
and wait for it to go high if necessary.
2. Check the EEBUSY flag (EECON.0) and wait for it to go low if necessary
3. Disable interrupts if any interrupt routine accesses external data memory in the range
0000H–0FFFH
4. Set bit EEE in EECON register
5. Set bit LDPG in EECON register
6. Load DPTR (or DPTRB) with the address to write
7. Load the accumulator (ACC) with the data to be written
8. Execute MOVX @DPTR, A (or MOVX @/DPTR, A)
9. Repeat steps 6–8 for the first N-1 bytes
10. Clear bit LDPG in EECON register
11. Load DPTR (or DPTRB) with the address of byte N. The page address is set by the
address of this byte
12. Load the accumulator (ACC) with the data to be written
13. Execute MOVX @DPTR, A (or MOVX @/DPTR, A)
14. Clear bit EEE in EECON register
15. Restore interrupts if disabled in #3
16. The EEBUSY flag is set by hardware to indicate that programming is in progress and
that the EEPROM is not available for reading and writing
17. The end of programming is indicated by a hardware clear of EEBUSY
24
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 3-17. EEPROM Page Write of Five Bytes
EEE
LDPG
EEBUSY
tWC
MOVX
3.5.3
Erase
During a write sequence, individual EEPROM bytes are erased and then written in one atomic
operation. The entire 4KB EEPROM is normally erased when a Chip Erase command is issued
by the In-System Programming (ISP) interface. If this behavior is not desired, a user configuration fuse exists to disable chip erase of the EEPROM. See Section 23.2 on page 192. The entire
EERPROM is never erased by the bootloader or Flash API.
3.5.4
EEPROM Register
Table 3-5.
EECON – EEPROM Control Register
EECON = D2H
Reset Value = 1000 XX0XB
Not Bit Addressable
Bit
FOUT
AERS
LDPG
FLGE
INHIBIT
ERR
EEE
EEBUSY
7
6
5
4
3
2
1
0
Symbol
Function
FOUT
When FLGE = 1, FOUT is set/cleared by hardware during reads from EDATA in the range of 0780H–07FFH to show the
byte flag status of the last location accessed. FOUT = 1 when FLGE = 0.
AERS
Auto-Erase Enable. Set to perform an auto-erase of a Flash memory page during the next write sequence. Clear to
perform write without erase. This bit is reserved for the Flash API.
LDPG
Load Page Enable. Set to this bit to load multiple bytes to the temporary page buffer. Byte locations may not be loaded
more than once before a write. LDPG must be cleared before writing.
FLGE
Byte Flag Enable. When FLGE = 1, writes to EDATA in the range of 0780H–07FFH will set the byte flag of the location
accessed. Reads in the range of 0780H–07FFH will return the byte flag status in FOUT. When FLGE = 0 all byte flags
are reset to zero.
INHIBIT
Write Inhibit Flag. Cleared by hardware when the voltage on VDD has fallen below the minimum programming voltage.
Set by hardware when the voltage on VDD is above the minimum programming voltage (after 2 ms delay).
ERR
Error Flag. Set by hardware if an error occurred during the last programming sequence (Flash or EEPROM) due to a
brownout condition (low voltage on VDD). Must be cleared by software.
EEE
EEPROM Enable. Set to enable EEPROM and map it into the FDATA space 0000H–0FFFH. Clear to disable EEPROM
and access EDATA/XDATA in the 0000H–0FFFH address space.
BUSY
Busy Flag. Set by hardware when programming is in progress. Cleared by hardware when programming is complete.
25
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
3.6
Extended Stack
The AT89LP51RD2/ED2/ID2 provides an extended stack space for applications requiring additional stack memory. By default the stack is located in the 256-byte IDATA space of internal data
memory. The IDATA stack is referenced solely by the 8-bit Stack Pointer (SP: 81H). Setting the
XSTK bit in AUXR1 (see Table 5-6) enables the extended stack. The extended stack resides in
the EDATA space for up to 2KB of stack memory. The extended stack is referenced by an 11-bit
pointer formed from SP and the three LSBs of the Extended Stack Pointer (SPX: EFH) as shown
in Figure 3-18. SP is shared between both stacks. Note that the standard IDATA stack will not
overflow to the EDATA stack or vice versa. The stack and extended stack are mutually exclusive
and SPX is ignored when XTSK = 0. An application choosing to switch between stacks by toggling XSTK must maintain separate copies of SP for use with each stack space. Interrupts
should be disabled while swapping copies of SP in such an application to prevent illegal stack
accesses.
All interrupt calls and PUSH, POP, ACALL, LCALL, RET and RETI instructions will incur a one
or two-cycle penalty while the extended stack is enabled, depending on the number of stack
access in each instruction. The extended stack may only exist within the internal EDATA space;
it cannot be placed in XDATA. The stack will continue to use EDATA even if EDATA is disabled
by setting EXRRAM = 1 or if EEPROM is mapped in the same address space with EEE = 1.
Figure 3-18. Stack Configurations
7FFh
EDATA
(2K)
FFh
7
IDATA
(256)
0
2 07
SPX
0
SP
SP
00h
00h
XSTK = 0
26
XSTK = 1
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
4. Special Function Registers
A map of the on-chip memory area called the Special Function Register (SFR) space is shown in
Table 4-1.
Note that not all of the addresses are occupied, and unoccupied addresses may not be implemented on the chip. Read accesses to these addresses will in general return random data, and
write accesses will have an indeterminate effect. User software should not write to these unlisted
locations, since they may be used in future products to invoke new features.
Table 4-1.
Atmel AT89LP51RD2/ED2/ID2 SFR Map and Reset Values
8
0F8H
0F0H
9
A
B
C
D
E
CH
0000 0000
CCAP0H
0000 0000
CCAP1H
0000 0000
CCAP2H
0000 0000
CCAP3H
0000 0000
CCAP4H
0000 0000
RL0
0000 0000
RL1
0000 0000
RH0
0000 0000
RH1
0000 0000
PAGE
0000 0000
BX
0000 0000
0F7H
CL
0000 0000
CCAP0L
0000 0000
CCAP1L
0000 0000
CCAP2L
0000 0000
CCAP3L
0000 0000
CCAP4L
0000 0000
SPX
xxxx x000
0EFH
P0M1
0000 0000
0E7H
B
0000 0000
0E8H
0E0H
ACC
0000 0000
AX
0000 0000
DSPR
0000 0000
FIRD
0000 0000
MACL
0000 0000
MACH
0000 0000
P0M0
0D8H
CCON
00x0 0000
CMOD
00xx x000
CCAPM0
x000 0000
CCAPM1
x000 0000
CCAPM2
x000 0000
CCAPM3
x000 0000
CCAPM4
x000 0000
0D0H
PSW
0000 0000
FCON
xxxx 0000
EECON
0000 0000
DPLB
0000 0000
DPHB
0000 0000
P1M0
T2CON
0000 0000
T2MOD
0000 0000
RCAP2L
0000 000
RCAP2H
0000 0000
TL2
0000 000
TH2
0000 0000
P2M0
SPCON
0001 0100
SPSTA
0000 0000
SPDAT
xxxx xxxx
P3M0
AREF
0000 0000
P4M0
0C8H
0C0H
P4
1111 1111
0B8H
IPL0
xx00 0000
SADEN
0000 0000
0B0H
P3
1111 1111
IEN1
xxxx 0000
0A8H
IEN0
0x00 0000
SADDR
0000 0000
P2
1111 1111
DPCF
0000 xxxx
98H
SCON
0000 0000
90H
IPL1
xxxx 0000
(2)
(2)
(2)
(2)
(2)
IPH1
xxxx 0000
F
0FFH
0DFH
P1M1
0000 0000
0D7H
P2M1
0000 0000
0CFH
P3M1
0000 0000
0C7H
P4M1
0000 0000
0BFH
IPH0
xx00 0000
0B7H
ACSRB
0000 0000
DADL
0000 0000
DADH
0000 0000
CLKREG
0101 xxxx
CKCON1
xxxx xxx0
0AFH
AUXR1
0000 00x0
ACSRA
0000 0000
DADC
0000 0000
DADI
0000 0000
WDTRST
(write-only)
WDTPRG
0000 0xx0
0A7H
SBUF
xxxx xxxx
BRL
0000 0000
BDRCON
xxx0 0000
KBLS
0000 0000
KBE
0000 0000
KBF
0000 0000
KBMOD
0000 0000
9FH
P1
1111 1111
TCONB
0010 0100
BMSEL
xxxx xxx0
SSCON
0000 0000
SSCS
1111 1000
SSDAT
1111 1111
SSADR
1111 1110
CKRL
1111 1111
97H
88H
TCON
0000 0000
TMOD
0000 0000
TL0
0000 0000
TL1
0000 0000
TH0
0000 0000
TH1
0000 0000
AUXR
0000 0000
CKCON0
0000 0000
8FH
80H
P0
1111 1111
SP
0000 0111
DPL
0000 0000
DPH
0000 0000
CKSEL
xxxx xxx0
OSCCON
xxxx x001
PCON
000x 0000
87H
0
1
2
3
5
6
7
0A0H
Notes:
4
1. All SFRs in the left-most column are bit-addressable.
2. Reset value is 1111 1111B when Tristate-Port Fuse is enabled and 0000 0000B when disabled.
3. Reset value is 0101 0010B when Compatibility mode is enabled and 0000 0000B when disabled.
27
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
4.1
Register Summary
Table 4-2.
C51 Core SFRs
Mnemonic
Add
Name
ACC
E0h
Accumulator
B
F0h
B Register
PSW
D0h
Program Status Word
SP
81h
Stack Pointer
SPX
EFh
Extended Stack Pointer
DPL
82h
Data Pointer Low Byte
DPTR 7–0
DPH
83h
Data Pointer High Byte
DPTR 15–8
DPLB
D4h
Alternate Data Pointer Low Byte
DPTRB 7–0
DPHB
D5h
Alternate Data Pointer High Byte
DPTRB 15–8
PAGE
F6h
ERAM Page Register
Table 4-3.
7
6
5
4
3
2
1
0
RS0
OV
F1
P
SP10
SP9
SP8
ACC 7–0
B 7–0
CY
AC
F0
RS1
SP 7–0
–
–
–
–
SP11
–
–
–
–
PG3
PG2
PG1
PG0
7
6
5
4
3
2
1
0
CBE1
CBE0
MVCD
DPRB
Digital Signal Processing SFRs
Mnemonic
Add
Name
AX
E1h
Extended Accumulator
BX
F7h
Extended B Register
DSPR
E2h
DSP Control Register
FIRD
E3h
FIFO Depth
FIRD 7–0
MACL
E4h
MAC Low Byte
MAC 7–0
MACH
E5h
MAC High Byte
MAC 15–8
Table 4-4.
ACC 15–8
B 15–8
MRW1
MRW0
SMLB
SMLA
System Management SFRs
Mnemonic
Add
Name
7
6
5
4
3
2
1
0
PCON
87h
Power Control
SMOD1
SMOD0
PWDEX
POF
GF1
GF0
PD
IDL
AUXR
8Eh
Auxiliary Register 0
DPU
WS1
WS0/M0
XRS2
XRS1
XRS0
EXTRAM
AO
AUXR1
A2h
Auxiliary Register 1
–
–
ENBOOT
XSTK
GF3
0
–
DPS
DPCF
A1h
Datapointer Config Register
DPU1
DPU0
DPD1
DPD0
–
–
–
–
CKRL
97h
Clock Reload Register
CKCKON0
8Fh
Clock Control Register 0
TWIX2
WDTX2
PCAX2
SIX2
T2X2
T1X2
T0X2
X2
CKCKON1
AFh
Clock Control Register 1
–
–
–
–
–
–
–
SPIX2
85h
Clock Selection Register
–
–
–
–
–
–
–
CKS
AEh
Clock Register
TPS3
TPS2
TPS1
TPS0
–
–
–
–
85h
Oscillator Control Register
–
–
–
–
–
SCLKT0
OscBEn
OscAEn
(1)
CKSEL
CLKREG
(1)
OSCCON
Note:
28
1. Present on AT89LP51ID2 Only
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 4-5.
Interrupt SFRs
Mnemonic
Add
Name
7
6
5
4
3
2
1
0
IEN0
A8h
Interrupt Enable Control 0
EA
EC
ET2
ES
ET1
EX1
ET0
EX0
IEN1
B1h
Interrupt Enable Control 1
–
–
EADC
ECMP
–
ESPI
ETWI
EKB
IPH0
B7h
Interrupt Priority Control High 0
IP1D
PPCH
PT2H
PHS
PT1H
PX1H
PT0H
PX0H
IPL0
B8h
Interrupt Priority Control Low 0
IP0D
PPCL
PT2L
PLS
PT1L
PX1L
PT0L
PX0L
IPH1
B3h
Interrupt Priority Control High 1
IP3D
–
PADL
PCMPL
–
SPIH
PTWL
PKBH
IPL1
B2h
Interrupt Priority Control Low 1
IP2D
–
PADH
PCMPH
–
SPIL
PTWH
PKBL
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
FE/SM0
SM1
SM2
REN
TB8
RB8
TI
RI
–
–
–
BRR
TBCK
RBCK
SPD
SRC
Table 4-6.
Port SFRs
Mnemonic
Add
Name
P0
80h
8-bit Port 0
P1
90h
8-bit Port 1
P2
A0h
8-bit Port 2
P3
B0h
8-bit Port 3
P4
C0h
8-bit Port 4
P0M0
E6h
Port 0 Mode 0
P0M1
E7h
Port 0 Mode 1
P1M0
D6h
Port 1 Mode 0
P1M1
D7h
Port 1 Mode 1
P2M0
CEh
Port 2 Mode 0
P2M1
CFh
Port 2 Mode 1
P3M0
C6h
Port 3 Mode 0
P3M1
C7h
Port 3 Mode 1
P4M0
BEh
Port 4 Mode 0
P4M1
BFh
Port 4 Mode 1
Table 4-7.
Serial I/O Port SFRs
Mnemonic
Add
Name
SCON
98h
Serial Control
SBUF
99h
Serial Data Buffer
SADEN
B9h
Slave Address Mask
SADDR
A9h
Slave Address
BDRCON
9Bh
Baud Rate Control
BRL
9Ah
Baud Rate Reload
29
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 4-8.
Timer SFRs
Mnemonic
Add
Name
7
6
5
4
3
2
1
0
TCON
88h
Timer/Counter 0 and 1 Control
TF1
TR1
TF0
TR0
IE1
IT1
IE0
IT0
TMOD
89h
Timer/Counter 0 and 1 Modes
GATE1
C/T1
M11
M01
GATE0
C/T0
M10
M00
TCONB
91h
Timer/Counter 0 and 1 Mode B
PWM1EN PWM0EN
PSC12
PSC11
PSC10
PSC02
PSC01
PSC00
TL0
8Ah
Timer/Counter 0 Low Byte
TH0
8Ch
Timer/Counter 0 High Byte
TL1
8Bh
Timer/Counter 1 Low Byte
TH1
8Dh
Timer/Counter 1 High Byte
RL0
F2h
Timer/Counter 0 Reload Low
RH0
F3h
Timer/Counter 0 Reload High
RTL1
F4h
Timer/Counter 1 Reload Low
RH1
F5h
Timer/Counter 1 Reload High
WDTRST
A6h
WatchDog Timer Reset
WDTPRG
A7h
WatchDog Timer Program
WDTOVF
SWRST
WDTEN
WDIDLE
DISRTO
WTO2
WTO1
WTO0
T2CON
C8h
Timer/Counter 2 control
TF2
EXF2
RCLK
TCLK
EXEN2
TR2
C/T2
CP/RL2
T2MOD
C9h
Timer/Counter 2 Mode
–
–
–
–
–
–
T2OE
DCEN
RCAP2H
CBh
Timer/Counter 2 Reload/Capture
High Byte
RCAP2L
CAh
Timer/Counter 2 Reload/Capture
Low Byte
TH2
CDh
Timer/Counter 2 High Byte
TL2
CCh
Timer/Counter 2 Low Byte
7
6
5
4
3
2
1
0
Table 4-9.
SPI Controller SFRs
Mnemonic
Add
Name
SPCON
C3h
SPI Control
SPR2
SPEN
SSDIS
MSTR
CPOL
CPHA
SPR1
SPR0
SPSTA
C4h
SPI Status
SPIF
WCOL
SSERR
MODF
TXE
DORD
REMAP
TBIE
SPDAT
C5h
SPI Data
SPD7
SPD6
SPD5
SPD4
SPD3
SPD2
SPD1
SPD0
7
6
5
4
3
2
1
0
Table 4-10.
TWI Controller SFRs
Mnemonic
Add
Name
SSCON
93h
Synchronous Serial Control
SSCR2
SSPE
SSSTA
SSSTO
SSI
SSAA
SSCR1
SSCR0
SSCS
94h
Synchronous Serial Status
SSC4
SSC3
SSC2
SSC1
SSC0
0
0
0
SSDAT
95h
Synchronous Serial Data
SSADR
96h
Synchronous Serial Address
SSA7
SSA6
SSA5
SSA4
SSA3
SSA2
SSA1
SSGC
30
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 4-11.
Keyboard Interface SFRs
Mnemonic
Add
Name
7
6
5
4
3
2
1
0
KBLS
9Ch
Keyboard Level Selector
KBLS7
KBLS6
KBLS5
KBLS4
KBLS3
KBLS2
KBLS1
KBLS0
KBE
9Dh
Keyboard Input Enable
KBE7
KBE6
KBE5
KBE4
KBE3
KBE2
KBE1
KBE0
KBF
9Eh
Keyboard Flag Register
KBF7
KBF6
KBF5
KBF4
KBF3
KBF2
KBF1
KBF0
KBMOD
9Fh
Keyboard Mode Register
KBM7
KBM6
KBM5
KBM4
KBM3
KBM2
KBM1
KBM0
Table 4-12.
Flash/EEPROM Memory SFR
Mnemonic
Add
Name
7
6
5
4
3
2
1
0
BMSEL
92h
Bank Mode Select Register
–
–
–
–
–
–
–
FBS
FCON
D2h
Flash Control Register
FPL3
FPL2
FPL1
FPL0
FPS
FMOD1
FMOD0
FBUSY
EECON
D2h
EEPROM Control Register
FOUT
AERS
LDPG
FLGE
INHIBIT
ERR
EEE
EEBUSY
7
6
5
4
3
2
1
0
Table 4-13.
Analog Comparator SFRs
Mnemonic
Add
Name
ACSRA
A3h
Comparator A Control Register
CSA1
CSA0
CONA
CFA
CENA
CMA
CMA1
CMA0
ACSRB
ABh
Comparator B Control Register
CSB1
CSB0
CONB
CFB
CENB
CMB
CMB1
CMB0
AREF
BDh
Comparator Reference Register
CMPB
CMPA
RFB1
RFB0
CCS1
CCS0
RFA1
RFA0
7
6
5
4
3
2
1
0
ADIF
GO/BSY
DAC
ADCE
LADJ
ACK2
ACK1
ACK0
ACON
IREF
TRG1
TRG0
DIFF
ACS2
ACS1
ACS0
Table 4-14.
ADC Controller SFRs
Mnemonic
Add
Name
DADC
A4h
DAC/ADC Control Register
DADI
A5h
DAC/ADC Input Register
DADL
ACh
DAC/ADC Data Low Register
–
–
–
–
–
–
ADAT9
ADAT8
DADH
ADh
DAC/ADC Data High Register
ADAT7
ADAT6
ADAT5
ADAT4
ADAT3
ADAT2
ADAT1
ADAT0
7
6
5
4
3
2
1
0
CF
CR
–
CCF4
CCF3
CCF2
CCF1
CCF0
CIDL
WDTE
–
–
–
CPS1
CPS0
ECF
CCAPM0 DAh PCA Timer/Counter Mode 0
–
ECOM0
CAPP0
CAPN0
MAT0
TOG0
PWM0
ECCF0
CCAPM1 DBh PCA Timer/Counter Mode 1
–
ECOM1
CAPP1
CAPN1
MAT1
TOG1
PWM1
ECCF1
CCAPM2 DCh PCA Timer/Counter Mode 2
–
ECOM2
CAPP2
CAPN2
MAT2
TOG2
PWM2
ECCF2
Table 4-15.
PCA SFRs
Mnemo
-nic
Add Name
CCON
D8h
PCA Timer/Counter Control
CMOD
D9h
PCA Timer/Counter Mode
CL
E9h
PCA Timer/Counter Low Byte
CH
F9h
PCA Timer/Counter High Byte
31
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 4-15.
Mnemo
-nic
PCA SFRs (Continued)
Add Name
7
6
5
4
3
2
1
0
CCAPM3 DDh PCA Timer/Counter Mode 3
–
ECOM3
CAPP3
CAPN3
MAT3
TOG3
PWM3
ECCF3
CCAPM4 DEh PCA Timer/Counter Mode 4
–
ECOM4
CAPP4
CAPN4
MAT4
TOG4
PWM4
ECCF4
CCAP0H FAh
PCA Compare Capture Module 0 H CCAP0H7 CCAP0H6 CCAP0H5 CCAP0H4 CCAP0H3 CCAP0H2 CCAP0H1 CCAP0H0
CCAP1H FBh
PCA Compare Capture Module 1 H CCAP1H7 CCAP1H6 CCAP1H5 CCAP1H4 CCAP1H3 CCAP1H2 CCAP1H1 CCAP1H0
CCAP2H FCh PCA Compare Capture Module 2 H CCAP2H7 CCAP2H6 CCAP2H5 CCAP2H4 CCAP2H3 CCAP2H2 CCAP2H1 CCAP2H0
CCAP3H FDh PCA Compare Capture Module 3 H CCAP3H7 CCAP3H6 CCAP3H5 CCAP3H4 CCAP3H3 CCAP3H2 CCAP3H1 CCAP3H0
CCAP4H FEh
PCA Compare Capture Module 4 H CCAP4H7 CCAP4H6 CCAP4H5 CCAP4H4 CCAP4H3 CCAP4H2 CCAP4H1 CCAP4H0
CCAP0L
EAh PCA Compare Capture Module 0 L CCAP0L7 CCAP0L6 CCAP0L5 CCAP0L4 CCAP0L3 CCAP0L2 CCAP0L1 CCAP0L0
CCAP1L
EBh PCA Compare Capture Module 1 L CCAP1L7 CCAP1L6 CCAP1L5 CCAP1L4 CCAP1L3 CCAP1L2 CCAP1L1 CCAP1L0
CCAP2L
ECh PCA Compare Capture Module 2 L CCAP2L7 CCAP2L6 CCAP2L5 CCAP2L4 CCAP2L3 CCAP2L2 CCAP2L1 CCAP2L0
CCAP3L
EDh PCA Compare Capture Module 3 L CCAP3L7 CCAP3L6 CCAP3L5 CCAP3L4 CCAP3L3 CCAP3L2 CCAP3L1 CCAP3L0
CCAP4L
EEh PCA Compare Capture Module 4 L CCAP4L7 CCAP4L6 CCAP4L5 CCAP4L4 CCAP4L3 CCAP4L2 CCAP4L1 CCAP4L0
4.2
Register Index
Table 4-16.
Special Function Register Cross Reference
Name
Address
ACC
E0H
ACSRA
A3H
ACSRB
Name
Address
Description Index
CCAP3L
EDH
Table 14-8 on page 104
Table 19-1 on page 165
CCAP4H
FEH
Table 14-7 on page 104
ABH
Table 19-2 on page 166
CCAP4L
EEH
Table 14-8 on page 104
AREF
BDH
Table 19-3 on page 167
CCAPM0
DAH
AUXR
8EH
Table 3-3 on page 19
CCAPM1
DBH
AUXR1
A2H
Table 5-6 on page 41
CCAPM2
DCH
AX
E1H
Section 5.3 on page 36
CCAPM3
DDH
B
F0H
CCAPM4
DEH
BDRCON
9BH
Table 16-7 on page 118
CH
F9H
Table 14-4 on page 101
BMSEL
92H
Table 3-2 on page 13
CKCON0
8FH
Table 6-9 on page 52
BRL
9AH
Table 16-6 on page 117
CKCON1
AFH
Table 6-10 on page 54
BX
F1H
Section 5.3 on page 36
CKRL
97H
Table 6-7 on page 51
CCON
D8H
Table 14-3 on page 101
CKSEL
85H
Table 6-4 on page 50
CCAP0H
FAH
Table 14-7 on page 104
CL
E9H
Table 14-5 on page 102
CCAP0L
EAH
Table 14-8 on page 104
CLKREG
AEH
Table 6-8 on page 51
CCAP1H
FBH
Table 14-7 on page 104
CMOD
D9H
Table 14-2 on page 100
CCAP1L
EBH
Table 14-8 on page 104
DADC
A4H
Table 20-2 on page 174
CCAP2H
FCH
Table 14-7 on page 104
DADH
ADH
Table 20-5 on page 176
CCAP2L
ECH
Table 14-8 on page 104
DADI
A5H
Table 20-3 on page 175
CCAP3H
FDH
Table 14-7 on page 104
DADL
ACH
Table 20-4 on page 176
32
Description Index
Table 14-6 on page 103
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 4-16.
Special Function Register Cross Reference (Continued)
DPCF
A1H
DPH
83H
DPHB
D5H
Table 5-7 on page 41
PSW
D0H
RCAP2H
CBH
RCAP2L
CAH
Section 5.4 on page 39
DPL
82H
RH0
F4H
DPLB
D4H
RH1
F5H
DSPR
E2H
Table 5-1 on page 38
RL0
F2H
EECON
D2H
Table 3-5 on page 25
RL1
F3H
FCON
D1H
Table 23-10 on page 202
SADDR
A9H
Table 16-8 on page 120
FIRD
E3H
Section 5.4.2.3 on page 43
SADEN
B9H
Table 16-9 on page 120
IEN0
A8H
Table 9-3 on page 67
SBUF
99H
IEN1
B1H
Table 9-4 on page 67
SCON
98H
IPH0
B7H
Table 9-7 on page 69
SP
81H
IPH1
B3H
Table 9-8 on page 69
SPCON
C3H
Table 17-3 on page 136
IPL0
B8H
Table 9-5 on page 68
SPDAT
C5H
Table 17-4 on page 137
IPL1
B2H
Table 9-6 on page 68
SPSTA
C4H
Table 17-5 on page 137
KBE
9DH
Table 11-3 on page 72
SPX
EFH
Section 3.6 on page 26
KBF
9EH
Table 11-4 on page 72
SSADR
96H
Table 18-4 on page 146
KBLS
9CH
Table 11-2 on page 72
SSCON
93H
Table 18-2 on page 145
KBMOD
9FH
Table 11-1 on page 72
SSCS
94H
Table 18-3 on page 146
MACH
E5H
Section 5.3 on page 36
SSDAT
95H
Table 18-5 on page 146
MACL
E4H
Section 5.3 on page 36
T2CON
C8H
Table 13-3 on page 93
OSSCON
86H
Table 6-5 on page 50
T2MOD
C9H
Table 13-4 on page 94
P0
80H
Table 11-7 on page 74
TCON
88H
Table 12-2 on page 82
P0M0
E6H
TCONB
91H
Table 12-4 on page 84
P0M1
E7H
Table 11-6 on page 74 and Table
11-7 on page 74
TH0
8CH
P1
90H
Table 11-7 on page 74
TH1
8DH
P1M0
D6H
TH2
CDH
P1M1
D7H
Table 11-6 on page 74 and Table
11-7 on page 74
TL0
8AH
P2
A0H
Table 11-7 on page 74
TL1
8BH
P2M0
DEH
TL2
CCH
P2M1
CFH
Table 11-6 on page 74 and Table
11-7 on page 74
TMOD
89H
Table 12-3 on page 83
P3
B0H
Table 11-7 on page 74
WDTPRG
A7H
Table 15-2 on page 110
P3M0
C6H
WDTRST
A6H
Table 15-3 on page 110
P3M1
C7H
Table 11-6 on page 74 and Table
11-7 on page 74
P4
C0H
Table 11-7 on page 74
P4M0
BEH
P4M1
BFH
Table 11-6 on page 74 and Table
11-7 on page 74
PAGE
F6H
Table 3-4 on page 22
PCON
87H
Table 8-1 on page 59
Table 12-1 on page 82
Table 16-1 on page 112
Table 12-1 on page 82
Table 12-1 on page 82
33
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
5. Enhanced CPU
The AT89LP51RD2/ED2/ID2 uses an enhanced 8051 CPU that runs at 6 to 12 times the speed
of standard 8051 devices (or 3 to 6 times the speed of X2 8051 devices). The increase in performance is due to two factors. First, the CPU fetches one instruction byte from the code memory
every clock cycle. Second, the CPU uses a simple two-stage pipeline to fetch and execute
instructions in parallel. This basic pipelining concept allows the CPU to obtain up to
1 MIPS per MHz. The AT89LP51RD2/ED2/ID2 also has a Compatibility mode that preserves the
12-clock machine cycle of standard 8051s like the AT89C51RD2/ED2/ID2.
5.1
Fast Mode
Fast (Single-Cycle) mode must be enabled by clearing the Compatibility User Fuse. (See “User
Configuration Fuses” on page 192.) In this mode one instruction byte is fetched every system
clock cycle. The 8051 instruction set allows for instructions of variable length from 1 to 3 bytes.
In a single-clock-per-byte-fetch system this means each instruction takes at least as many
clocks as it has bytes to execute. The majority of instructions in the AT89LP51RD2/ED2/ID2 follow this rule: the instruction execution time in system clock cycles equals the number of bytes
per instruction, with a few exceptions. Branches and Calls require an additional cycle to compute the target address and some other complex instructions require multiple cycles. See
“Instruction Set Summary” on page 177. for more detailed information on individual instructions.
Example of Fast mode instructions are shown in Figure 5-1. Note that Fast mode instructions
take three times as long to execute if they are fetched from external program memory.
Figure 5-1.
Instruction Execution Sequences in Fast Mode
CLK
READ NEXT
OPCODE
S1
(A) 1-byte, 1-cycle instruction, e.g. INC A
READ OPERAND
READ NEXT OPCODE
S1
S2
(B) 2-byte, 2-cycle instruction, e.g. ADD A, #data
READ NEXT OPCODE
S1
S2
(C) 1-byte, 2-cycle instruction, e.g. INC DPTR
READ NEXT
OPCODE
S1
S2
ADDR
S3
S4
DATA
ACCESS EXTERNAL
MEMORY
(D) MOVX (1-byte, 4-cycle)
35
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
5.2
Compatibility Mode
Compatibility (12-Clock) mode is enabled by default from the factory or by setting the Compatibility User Fuse. In Compatibility mode instruction bytes are fetched every three system clock
cycles and the CPU operates with 6-state machine cycles and a divide-by-2 system clock for 12
oscillator periods per machine cycle. Standard instructions execute in1, 2 or 4 machine cycles.
Instruction timing in this mode is compatible with standard 8051s such as the
AT89C51RD2/ED2/ID2. In Compatibility mode there is no difference in timing between instructions executed from internal versus external program memory.
Compatibility mode can be used to preserve the execution profiles of legacy applications. For a
summary of differences between Fast and Compatibility modes see Table 2-3 on page 10.
Examples of Compatibility mode instructions are shown in Figure 5-2.
Figure 5-2.
Instruction Execution Sequences in Compatibility Mode
S1
S2
S3
S4
S5
S6
S1
S2
S3
S4
S5
S6
S1
CLK
ALE
READ OPCODE
S1
S2
S3
S4
READ NEXT
OPCODE
(DISCARD)
S5
READ NEXT OPCODE AGAIN
S6
(A) 1-byte, 1-cycle instruction, e.g., INC A
READ OPCODE
READ 2ND
BYTE
S1
S2
S3
S4
S5
(B) 2-byte, 1-cycle instruction, e.g., ADD A, #data
S2
S3
S4
S6
READ NEXT
OPCODE (DISCARD)
READ OPCODE
S1
READ NEXT OPCODE
S5
S6
S1
S2
READ NEXT
OPCODE AGAIN
S3
S4
S5
S6
(C) 1-byte, 2-cycle instruction, e.g., INC DPTR
READ
OPCODE
(MOVX)
S1
S2
(D) MOVX (1-byte, 2-cycle)
S3
READ NEXT
NO
OPCODE (DISCARD) FETCH
S4
S5
ADDR
S6
S1
NO READ NEXT
FETCH
OPCODE
AGAIN
NO
ALE
S2
S3
S4
S5
S6
DATA
DA
ACCESS EXTERNAL MEMOR
MEMORY
5.3
Multiply–Accumulate Unit (MAC)
The AT89LP51RD2/ED2/ID2 includes a multiply and accumulate (MAC) unit that can significantly speed up many mathematical operations required for digital signal processing. The MAC
unit includes a 16-by-16 bit multiplier and a 40-bit adder that can perform integer or fractional
multiply-accumulate operations on signed 16-bit input values. The MAC unit also includes a 1-bit
arithmetic shifter that will left or right shift the contents of the 40-bit MAC accumulator register
(M).
36
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
A block diagram of the MAC unit is shown in Figure 5-3. The 16-bit signed operands are provided by the register pairs (AX,ACC) and (BX,B) where AX (E1H) and BX (F7H) hold the higher
order bytes. The 16-by-16 bit multiplication is computed through partial products using the
AT89LP51RD2/ED2/ID2’s 8-bit multiplier. The 32-bit signed product is added to the 40-bit M
accumulator register. The MAC operation is summarized as follows:
M  M + {AX, ACC}  {BX, B}
MAC AB:
All computation is done in signed two’s complement form.
Figure 5-3.
Multiply–Accumulate Unit
AX
SMLA
SMLB
ACC
BX
B
16 x 16-bit Signed MULT
40-bit ADD
PSW
MRW
M4
M3
M2
Shifter
M1
M0
MACH
MACL
The MAC operation is performed by executing the MAC AB (A5 A4H) extended instruction. This
two-byte instruction requires nine clock cycles to complete as the multiply is done in a sequential
manner using partial products. The operand registers are not modified by the instruction and the
result is stored in the 40-bit M register. MAC AB also updates the C and OV flags in PSW. C represents the sign of the MAC result and OV is the two’s complement overflow. Note that MAC AB
will not clear OV if it was previously set to one.
Three additional extended instructions operate directly on the M register. CLR M (A5 E4H)
clears the entire 40-bit register in two clock cycles. LSL M (A5 23H) and ASR (A5 03H) shift M
one bit to the left and right respectively. Right shifts are done arithmetically, i.e. the sign is
preserved.
The 40-bit M register is accessible 16-bits at a time through a sliding window as shown in Figure
5-4. The MRW1-0 bits in DSPR (Table 5-1) select which 16-bit segment is currently accessible
through the MACL and MACH addresses. For normal fixed point operations the window can be
fixed to the rank of interest. For example, multiplying two 1.15 format numbers places a 2.30 format result in the M register. If MRW is set to 10B, a 1.15 value is obtained after performing a
single LSL M.
37
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 5-4.
M Register with Sliding Window
M
Byte 4
Byte 3
Byte 2
Byte 1
Byte 0
39 – 32
31 – 24
23 – 16
15 – 8
7–0
MACH
MACL
MACH
MACH
MACH
MACL
MRW1-0 = 00B
MRW1-0 = 01B
MACL
MRW1-0 = 10B
MACL
MRW1-0 = 11B
As a consequence of the MAC unit, the standard 8x8 MUL AB instruction can support signed
multiplication. The SMLA and SMLB bits in DSPR control the multiplier’s interpretation of the
ACC and B registers, allowing any combination of signed and unsigned operand multiplication.
These bits have no effect on the MAC operation which always multiplies signed-by-signed.
Table 5-1.
DSPR – Digital Signal Processing Configuration Register
DSPR = E2H
Reset Value = 0000 0000B
Not Bit Addressable
Bit
MRW1
MRW0
SMLB
SMLA
CBE1
CBE0
MVCD
DPRB
7
6
5
4
3
2
1
0
Symbol
Function
MRW1-0
M Register Window. Selects which pair of bytes from the 5-byte M register is accessible through MACH (E5H) and
MACL (E4H) as shown in Figure 5-4. For example, MRW = 10B for normal 16-bit fixed-point operations where the lowest
order portion of the fractional result is discarded.
SMLB
Signed Multiply Operand B. When SMLB = 0, the MUL AB instruction treats the contents of B as an unsigned value.
When SMLB = 1, the MUL AB instruction interprets the contents of B as a signed two’s complement value. SMLB does
not affect the MAC operation.
SMLA
Signed Multiply Operand A. When SMLA = 0, the MUL AB instruction treats the contents of ACC as an unsigned value.
When SMLA = 1, the MUL AB instruction interprets the contents of ACC as a signed two’s complement value. SMLA
does not affect the MAC operation.
CBE1
DPTR1 Circular Buffer Enable. Set CBE1 = 1 to configure DPTR1 for circular addressing over the two circular buffer
address ranges. Clear CBE1 for normal DPTR operation.
CBE0
DPTR0 Circular Buffer Enable. Set CBE0 = 1 to configure DPTR0 for circular addressing over the two circular buffer
address ranges. Clear CBE0 for normal DPTR operation.
MVCD
MOVC Index Disable. When MVCD = 0, the MOVC A, @A+DPTR instruction functions normally with indexed
addressing. Setting MVCD = 1 disables the indexed addressing mode such that MOVC A, @A+DPTR functions as
MOVC A, @DPTR.
DPRB
DPTR1 Redirect to B. DPRB selects the source/destination register for MOVC/MOVX instructions that reference DPTR1.
When DPRB = 0, ACC is the source/destination. When DPRB = 1, B is the source/destination. DPRB does not change
the index register for MOVC instructions.
38
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
5.4
Enhanced Dual Data Pointers
The AT89LP51RD2/ED2/ID2 provides two 16-bit data pointers: DPTR0 and DPTR1. The data
pointers are used by several instructions to access the program or data memories. The
Auxiliary 1 Register (AUXR1) and Data Pointer Configuration Register (DPCF) control operation
of the dual data pointers (see Table 5-6 on page 41 and Table 5-7 on page 41). The DPS bit in
AUXR1 selects which data pointer is currently referenced by instructions including the DPTR
operand. Each data pointer may also be accessed at a pair of SFR addresses that also depend
on the DPS value. The data pointer referenced by DPS is located at the register pair DPL and
DPH (82H an 83H), and the alternate data pointer not referenced by DPS is located at the register pair DPLB and DPHB (D4H and D5H). When DPS is toggled, the two data pointers also swap
which SFR pair will access them as shown in Table 5-2. The AT89LP51RD2/ED2/ID2 provides
two methods for fast context switching of the data pointers:
• Bit 2 of AUXR1 is hard-wired as a logic 0. The DPS bit may be toggled (to switch data
pointers) simply by incrementing the AUXR1 register, without altering other bits in the register
unintentionally. This is the preferred method when only a single data pointer will be used at
one time.
EX:
INC
AUXR1 ; Toggle DPS
• In some cases, both data pointers must be used simultaneously. To prevent frequent toggling
of DPS, the AT89LP51RD2/ED2/ID2 supports a prefix notation for selecting the opposite data
pointer per instruction. All DPTR instructions, with the exception of JMP @A+DPTR, when
prefixed with an 0A5H opcode will use the inverse value of DPS (DPS) to select the data
pointer. Some assemblers may support this operation by using the /DPTR operand. For
example, the following code performs a block copy within EDATA:
MOV
AUXR1, #00H
MOV
DPTR, #SRC
; load source address to dptr0
MOV
/DPTR, #DST
; load destination address to dptr1
MOV
R7, #BLKSIZE
COPY: MOVX A, @DPTR
INC
DPTR
; DPS = 0
; number of bytes to copy
; read source (dptr0)
; next src (dptr0+1)
MOVX @/DPTR, A
; write destination (dptr1)
INC
; next dst (dptr1+1)
/DPTR
DJNZ R7, COPY
For assemblers that do not support this notation, the 0A5H prefix must be declared in-line:
EX:
DB
0A5H
INC
DPTR
Table 5-2.
; equivalent to INC /DPTR
Data Pointer Register Access
SFR
DPS = 0
DPS = 1
DPL (82H)
DP0L
DP1L
DPH (83H)
DP0H
DP1H
DPLB (D4H)
DP1L
DP0L
DPHB (D5H)
DP1H
DP0H
39
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
A summary of data pointer instructions with fast context switching is listed inTable 5-3.
Table 5-3.
Data Pointer Instructions
Operation
5.4.1
Instruction
DPS = 0
DPS = 1
JMP @A+DPTR
JMP @A+DPTR0
JMP @A+DPTR1
MOV DPTR, #data16
MOV DPTR0, #data16
MOV DPTR1, #data16
MOV /DPTR, #data16
MOV DPTR1, #data16
MOV DPTR0, #data16
INC DPTR
INC DPTR0
INC DPTR1
INC /DPTR
INC DPTR1
INC DPTR0
MOVC A,@A+DPTR
MOVC A,@A+DPTR0
MOVC A,@A+DPTR1
MOVC A,@A+/DPTR
MOVC A,@A+DPTR1
MOVC A,@A+DPTR0
MOVX A,@DPTR
MOVX A,@DPTR0
MOVX A,@DPTR1
MOVX A,@/DPTR
MOVX A,@DPTR1
MOVX A,@DPTR0
MOVX @DPTR, A
MOVX @DPTR0, A
MOVX @DPTR1, A
MOVX @/DPTR, A
MOVX @DPTR1, A
MOVX @DPTR0, A
Data Pointer Update
The Dual Data Pointers on the AT89LP51RD2/ED2/ID2 include two features that control how
the data pointers are updated. The data pointer decrement bits, DPD1 and DPD0 in AUXR1,
configure the INC DPTR instruction to act as DEC DPTR. The resulting operation will depend on
DPS as shown in Table 5-4. These bits also control the direction of auto-updates during MOVC
and MOVX.
Table 5-4.
Data Pointer Decrement Behavior
Equivalent Operation for INC DPTR and INC /DPTR
DPS = 0
DPS = 1
DPD1
DPD0
INC DPTR
INC /DPTR
INC DPTR
INC /DPTR
0
0
INC DPTR0
INC DPTR1
INC DPTR1
INC DPTR0
0
1
DEC DPTR0
INC DPTR1
INC DPTR1
DEC DPTR0
1
0
INC DPTR0
DEC DPTR1
DEC DPTR1
INC DPTR0
1
1
DEC DPTR0
DEC DPTR1
DEC DPTR1
DEC DPTR0
The data pointer update bits, DPU1 and DPU0, allow MOVX @DPTR and MOVC @DPTR
instructions to update the selected data pointer automatically in a post-increment or post-decrement fashion. The direction of update depends on the DPD1 and DPD0 bits as shown in Table
5-5. These bits can be used to make block copy routines more efficient. Note that DPCF should
be cleared to zero, disabling these modes, before any calls are made to the Flash API.Care
must also be taken when interrupt routines use data pointers to ensure that correct operation is
saved/restored correctly.
40
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 5-5.
Data Pointer Auto-Update
Update Operation for MOVX and MOVC (DPU1 = 1 & DPU0 = 1)
DPS = 0
DPS = 1
DPD1
DPD0
DPTR
/DPTR
DPTR
/DPTR
0
0
DPTR0++
DPTR1++
DPTR1++
DPTR0++
0
1
DPTR0--
DPTR1++
DPTR1++
DPTR0--
1
0
DPTR0++
DPTR1--
DPTR1--
DPTR0++
1
1
DPTR0--
DPTR1--
DPTR1--
DPTR0--
Table 5-6.
AUXR1 – Auxiliary Register 1
AUXR1 = A2H
Reset Value = XXX0 00X0B
Not Bit Addressable
Bit
–
–
ENBOOT
XSTK
GF3
0
–
DPS
7
6
5
4
3
2
1
0
Symbol
Function
ENBOOT
Set ENBOOT = 1 to map the Boot ROM in the range F800H–FFFFH. This is required to run the bootloader or access the
Flash API. When ENBOOT = 0 the Boot ROM is not accessible and normal program memory is mapped to this range.
The default value is set by the Bootloader Jump bit. See Section 23.2 on page 192.
XSTK
Extended Stack Enable. When XSTK = 0 the stack resides in IDATA and is limited to 256 bytes. Set XSTK = 1 to place
the stack in EDATA for up to 2K bytes of extended stack space. All PUSH, POP, CALL and RET instructions will incur a
one or two cycle penalty when accessing the extended stack.
GF3
This bit is a general purpose user flag.
DPS
Data Pointer Select. DPS selects the active data pointer for instructions that reference DPTR. When DPS = 0, DPTR will
target DPTR0 and /DPTR will target DPTR1. When DPS = 1, DPTR will target DPTR1 and /DPTR will target DPTR0.
Table 5-7.
DPCF – Data Pointer Configuration Register
DPCF = A1H
Reset Value = 0000 XXXXB
Not Bit Addressable
Bit
DPU1
DPU0
DPD1
DPD0
–
–
–
–
7
6
5
4
3
2
1
0
Symbol
Function
DPU1
Data Pointer 1 Update. When set, MOVX @DPTR and MOVC @DPTR instructions that use DPTR1 will also update
DPTR1 based on DPD1. If DPD1 = 0 the operation is post-increment and if DPD1 = 1 the operation is post-decrement.
When DPU1 = 0, DPTR1 is not updated.
DPU0
Data Pointer 0 Update. When set, MOVX @DPTR and MOVC @DPTR instructions that use DPTR0 will also update
DPTR0 based on DPD0. If DPD0 = 0 the operation is post-increment and if DPD0 = 1 the operation is post-decrement.
When DPU0 = 0, DPTR0 is not updated.
DPD1
Data Pointer 1 Decrement. When set, INC DPTR instructions targeted to DPTR1 will decrement DPTR1. When cleared,
INC DPTR instructions will increment DPTR1. DPD1 also determines the direction of auto-update for DPTR1 when
DPU1 = 1.
DPD0
Data Pointer 0 Decrement. When set, INC DPTR instructions targeted to DPTR0 will decrement DPTR0. When cleared,
INC DPTR instructions will increment DPTR0. DPD0 also determines the direction of auto-update for DPTR0 when
DPU0 = 1.
41
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
5.4.2
5.4.2.1
Data Pointer Operating Modes
The Dual Data Pointers on the AT89LP51RD2/ED2/ID2 include three additional operating
modes that affect data pointer based instructions. These modes are controlled by bits in DSPR.
Note that these bits in DSPR should be cleared to zero, disabling these modes, before any calls
are made to the Flash API.Care must also be taken when interrupt routines use data pointers to
ensure that correct operation is saved/restored correctly.
DPTR Redirect
The Data Pointer Redirect to B bit, DPRB (DSPR.0), allows MOVX and MOVC instructions to
use the B register as the data source/destination when the instruction references DPTR1 as
shown in Table 5-8 and Table 5-9. DPRB can improve the efficiency of routines that must fetch
multiple operands from different RAM locations.
Table 5-8.
MOVX @DPTR Operating Modes
Equivalent Operation for MOVX
MOVX A, @DPTR
5.4.2.2
MOVX @DPTR, A
DPRB
DPS
DPTR
/DPTR
DPTR
/DPTR
0
0
MOVX
A, @DPTR0
MOVX
A, @DPTR1
MOVX
@DPTR0, A
MOVX
@DPTR1, A
0
1
MOVX
A, @DPTR1
MOVX
A, @DPTR0
MOVX
@DPTR1, A
MOVX
@DPTR0, A
1
0
MOVX
A, @DPTR0
MOVX
B, @DPTR1
MOVX
@DPTR0, A
MOVX
@DPTR1, B
1
1
MOVX
B, @DPTR1
MOVX
A, @DPTR0
MOVX
@DPTR1, B
MOVX
@DPTR0, A
Index Disable
The MOVC Index Disable bit, MVCD (DSPR.1), disables the indexed addressing mode of the
MOVC A, @A+DPTR instruction. When MVCD = 1, the MOVC instruction functions as
MOVC A, @DPTR with no indexing as shown in Table 5-9. MVCD can improve the efficiency of
routines that must fetch multiple operands from program memory. DPRB can change the MOVC
destination register from ACC to B, but has no effect on the MOVC index register.
Table 5-9.
MOVC @DPTR Operating Modes
Equivalent Operation for MOVC A, @A+DPTR
DPS = 0
42
DPS = 1
MVCD
DPRB
DPTR
/DPTR
DPTR
/DPTR
0
0
MOVC
A, @A+DPTR0
MOVC
A, @A+DPTR1
MOVC
A, @A+DPTR1
MOVC
A, @A+DPTR0
0
1
MOVC
A, @A+DPTR0
MOVC
B, @A+DPTR1
MOVC
B, @A+DPTR1
MOVC
A, @A+DPTR0
1
0
MOVC
A, @DPTR0
MOVC
A, @DPTR1
MOVC
A, @DPTR1
MOVC
A, @DPTR0
1
1
MOVC
A, @DPTR0
MOVC
B, @DPTR1
MOVC
B, @DPTR1
MOVC
A, @DPTR0
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
5.4.2.3
Circular Buffers
The CBE0 and CBE1 bits in DSPR can configure DPTR0 and DPTR1, respectively, to operate in
circular buffer mode. The AT89LP51RD2/ED2/ID2 maps circular buffers into two identically
sized regions of EDATA/XDATA. These buffers can speed up convolution computations such as
FIR and IAR digital filters. The length of the buffers are set by the value of the FIRD (E3H) register for up to 256 entries. Buffer A is mapped from 0000H to FIRD and Buffer B is mapped from
0100H to 100H+FIRD as shown in Figure 5-5. Both data pointers may operate in either buffer.
When circular buffer mode is enabled, updates to a data pointer referencing the buffer region will
follow circular addressing rules. If the data pointer is equal to FIRD or 100H+FIRD any increment will cause it to overflow to 0000H or 0100H respectively. If the data pointer is equal to
0000H or 0100H any decrement will cause it to underflow to FIRD or 100H+FIRD respectively.
In this mode, updates can be either an explicit INC DPTR or an automatic update using DPUn
where the DPDn bits control the direction. The data pointer will increment or decrement normally
at any other addresses. Therefore, when circular addressing is in use, the data pointers can still
operate as regular pointers in the FIRD+1 to 00FFH and greater than 100H+FIRD ranges.
Figure 5-5.
Circular Buffer Mode
DPDn = 1
DPDn = 1
B
DPDn = 0
DPTR
DPDn = 0
100h + FIRD
0100h
FIRD
A
DPTR
0000h
5.5
Instruction Set Extensions
Table 5-10 lists the additions to the 8051 instruction set that are supported by the
AT89LP51RD2/ED2/ID2. For more information on the instruction set see Section 21. “Instruction
Set Summary” on page 177. For detailed descriptions of the extended instructions see Section
21.1 “Instruction Set Extensions” on page 181.
Table 5-10.
Opcode
AT89LP51RD2/ED2/ID2 Extended Instructions
Mnemonic
Description
Bytes
Cycles
A5 00
BREAK
Software breakpoint
2
2
A5 03
ASR M
Arithmetic shift right of M register
2
2
A5 23
LSL M
Logical shift left of M register
2
2
A5 73
JMP @A+PC
Indirect jump relative to PC
2
3
A5 90
MOV /DPTR, #data16
Move 16-bit constant to alternate data
pointer
4
4
A5 93
MOVC A, @A+/DPTR
Move code location to ACC relative to
alternate data pointer
2
4
A5 A3
INC /DPTR
Increment alternate data pointer
2
3
43
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 5-10.
Opcode
AT89LP51RD2/ED2/ID2 Extended Instructions
Mnemonic
Description
Bytes
Cycles
A5 A4
MAC AB
Multiply and accumulate
2
9
A5 B6
CJNE A, @R0, rel
Compare ACC to indirect RAM and
jump if not equal
3
4
A5 B7
CJNE A, @R1, rel
Compare ACC to indirect RAM and
jump if not equal
3
4
A5 E0
MOVX A, @/DPTR
Move external to ACC; 16-bit address
in alternate data pointer
2
3/5
A5 E4
CLR M
Clear M register
2
2
A5 F0
MOVX @/DPTR, A
Move ACC to external; 16-bit address
in alternate data pointer
2
3/5
• The /DPTR instructions provide support for the dual data pointer features described above
(See Section 5.4).
• The ASR M, LSL M, CLR M and MAC AB instructions are part of the Multiply-Accumulate
Unit (See Section 5.3).
• The JMP @A+PC instruction supports localized jump tables without using a data pointer.
• The CJNE A, @Ri, rel instructions allow compares of array values with non-constant values.
• The BREAK instruction is used by the On-Chip Debug system. See Section 22. on page 187.
• Some third party assemblers/compilers do not support these instructions. In order to use
them you may need to write assembly functions that emulate the instruction by declaring the
opcodes inline as shown in Table 5-11.
Table 5-11.
Opcode
44
Extended Instruction Assembly Emulations
Mnemonic
Emulation
A5 00
BREAK
DB A5H, 00H
A5 03
ASR M
DB A5H, 03H or DB A5H followed by RR A
A5 23
LSL M
DB A5H, 23H or DB A5H followed by RL A
A5 73
JMP @A+PC
DB A5H, 73H or DB A5H followed by JMP @A+DPTR
A5 90
MOV /DPTR, #data16
DB A5H followed by MOV DPTR, #data16
A5 93
MOVC A, @A+/DPTR
DB A5H, 93H or DB A5H followed by MOVC A, @A+DPTR
A5 A3
INC /DPTR
DB A5H, A3H or DB A5H followed by INC DPTR
A5 A4
MAC AB
DB A5H, A4H or DB A5H followed by MUL AB
A5 B6
CJNE A, @R0, rel
DB A5H, B6H, (LABEL-$-3) where LABEL is the jump target
A5 B7
CJNE A, @R1, rel
DB A5H, B7H, (LABEL-$-3) where LABEL is the jump target
A5 E0
MOVX A, @/DPTR
DB A5H, E0H or DB A5H followed by MOVX A, @DPTR
A5 E4
CLR M
DB E4H, E0H or DB A5H followed by CLR A
A5 F0
MOVX @/DPTR, A
DB A5H, F0H or DB A5H followed by MOVX @DPTR, A
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
6. System Clock
The AT89LP51RD2/ED2 has a single system clock that is generated directly from one of three
selectable clock sources: on-chip crystal oscillator A in high or low power operation, external
clock source on XTAL1A, and the internal 8 MHz RC oscillator. A diagram of the clock subsystem is shown in Figure 6-1. The clock source is selected by the Clock Source A User Fuses as
shown in Table 6-1 (See “User Configuration Fuses” on page 192). In addition to this system
clock, the AT89LP51ID2 device adds a second system clock source that is selectable from onchip low frequency crystal oscillator B in, external clock source on XTAL1B, and the internal 8
MHz RC oscillator. A diagram of this clock subsystem is shown in Figure 6-2. Clock source B is
selected by the Clock Source B User Fuses as shown in Table 6-2. The choice of clock source
also affects the start-up time after a POR, BOD or Power-down event (See “Reset” on page 55
or “Power-down Mode” on page 60).
The AT89LP51RD2/ED2/ID2 includes a X1/X2 feature for compatibility with
AT89C51RD2/ED2/ID2. This feature determines if the oscillator source is divided by two or not
to generate the system clock. The 8-bit system clock divider may be used to prescale the system
clock to reduce the operating frequency. In addition a 4-bit prescaler is available to change the
clocks of the peripherals.
Figure 6-1.
AT89LP51RD2/ED2 Clock Subsystem Diagram
CKRL
CLOCK FUSE A
X2 (CKCON0.0)
INTERNAL
8.0 MHz
OSC
CLKIRC
0
CLKEXT
1
CLKXTAL
2
CKRL != FFH
1
3
XTAL1A
8-BIT
CLOCK
DIVIDER
0
÷2
1
0
TPS3-0
4-BIT
PRESCALER
Timer 0
Timer 1
Timer 2
PCA
Watchdog
OSCA
SYSTEM CLOCK
(CLKSYS)
XTAL2A
Figure 6-2.
AT89LP51ID2 Clock Subsystem Diagram
CLOCK FUSE A
INTERNAL
8.0 MHz
OSC
CLKIRC
0
CLKEXTA
1
CLKXTALA
2
CKRL
CKS (CKSEL.0)
3
XTAL1A
OSCA
X2 (CKCON0.0)
CKRL != FFH
OscAEn (OSCON.0)
0
CLOCK FUSE B
XTAL2A
1
1
÷2
CLKIRC
0
CLKEXTB
1
CLKXTALB
2
1
0
4-BIT
PRESCALER
Timer 0
Timer 1
Timer 2
PCA
Watchdog
SYSTEM CLOCK
(CLKSYS)
3
XTAL1B
0
8-BIT
CLOCK
DIVIDER
TPS3-0
Timer 2
(EXTB or XTALB
only via T2 )
OSCB
XTAL2B
OscBEn (OSCON.1)
÷128
Timer 0 Subclock
45
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 6-1.
Clock Source A
Fuse 1
Clock Source A
Fuse 0
1
1
High Speed Crystal Oscillator A (f > 12 MHz)
1
0
Low Power Crystal Oscillator A (f  12 MHz)
0
1
External Clock on XTAL1A
0
0
Internal 8.0 MHz RC Oscillator
Table 6-2.
6.1
Clock Source A Settings
Selected Clock Source
Clock Source B Settings (AT89LP51ID2 Only)
Clock Source B
Fuse 1
Clock Source B
Fuse 0
1
–
Low Frequency Crystal Oscillator B (32 kHz)
0
1
External Clock on XTAL1B
0
0
Internal 8.0 MHz RC Oscillator
Selected Clock Source
Crystal Oscillator A
When enabled, internal inverting oscillator amplifier A is connected between XTAL1A and
XTAL2A for connection to an external quartz crystal or ceramic resonator. The oscillator may
operate in either high-speed or low-power mode. Low-power mode is intended for crystals of 12
MHz or less and consumes less power than the higher speed mode. The configuration as shown
in Figure 6-3 applies for both high and low power oscillators. Note that in some cases, external
capacitors C1 and C2 may be reduced due to the on-chip capacitance of the XTAL1A and
XTAL2A inputs (approximately 10 pF each). When using the crystal oscillator, P4.6 and P4.7 will
have their inputs and outputs disabled. Also, XTAL2A in crystal oscillator mode should not be
used to directly drive a board-level clock without a buffer.
An optional 5 M on-chip resistor can be connected between XTAL1A and GND. This resistor
can improve the startup characteristics of the oscillator especially at higher frequencies. The
resistor can be enabled/disabled with the R1 User Fuse (See “User Configuration Fuses” on
page 192.)
Figure 6-3.
Crystal Oscillator A Connections
C2
~10 pF
C1
R1
~10 pF
Note:
46
1.
~5 MΩ
C1, C2 = 5–15 pF for Crystals
= 5–15 pF for Ceramic Resonators
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
6.2
External Clock Source A
The external clock option disables the oscillator amplifier and allows XTAL1A to be driven
directly by an external clock source as shown in Figure 6-4. XTAL2A may be left unconnected,
used as general purpose I/O P4.7, or configured to output a divided version of the system clock.
Figure 6-4.
External Clock A Drive Configuration
NC GPIO
XTAL2A (P4.7)
EXTERNAL
OSCILLATOR
SIGNAL
XTAL1A (P4.6)
GND
6.3
Internal RC Oscillator
The AT89LP51RD2/ED2/ID2 has an Internal RC oscillator tuned to 8.0 MHz ±2.5%. When
enabled as clock source A, XTAL1A and XTAL2A may be used as P4.6 and P4.7 respectively.
For AT89LP51ID2 the internal oscillator can also be selected for clock source B, freeing up
XTAL1B and XTAL2B to act as P1.0 and P4.2 respectively. The frequency of the oscillator may
be adjusted within limits by changing the RC Calibration Byte stored at byte 384 of the User Signature Array. This location may be updated using the IAP interface or by an external device
programmer (User Signature location 0180H). See Section 23.1.2 “Atmel Signature Array” on
page 192. A copy of the factory calibration byte is stored at byte 8 of the Atmel Signature Array
(0008H in SIG space).
6.4
Crystal Oscillator B (AT89LP51ID2)
AT89LP51ID2 includes a second crystal oscillator for low-frequency (~32 KHz) operation. When
enabled, internal inverting oscillator amplifier B is connected between XTAL1B and XTAL2B for
connection to an external quartz crystal or ceramic resonator as shown in Figure 6-5. Note that
in some cases, external capacitors C1 and C2 may be reduced due to the on-chip capacitance
of the XTAL1B and XTAL2B inputs (approximately 10 pF each). An on-chip series resistance is
included between the amplifier and the XTAL2B pad to limit the drive level. In most cases an
external series resistor is not required. When using the crystal oscillator, P1.0 and P4.2 will have
their inputs and outputs disabled. Also, XTAL2B in crystal oscillator mode should not be used to
directly drive a board-level clock without a buffer.
Please note that the low-frequency oscillator may have a very long settling time. The system
must ensure that the oscillator has sufficient time to stabilize before the device is allowed to
operate from this clock source.
47
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 6-5.
Crystal Oscillator B Connections
C2
XTAL2B
Rd
~10 pF
C1
XTAL1B
~10 pF
Note:
6.5
1.
C1, C2 = 10–20 pF for Crystals
= 10–20 pF for Ceramic Resonators
External Clock Source B (AT89LP51ID2)
The external clock option of AT89LP51ID2 disables the oscillator amplifier B and allows XTAL1B
to be driven directly by an external clock source as shown in Figure 6-6. XTAL2B may be left
unconnected or used as general purpose I/O P4.2.
Figure 6-6.
External Clock A Drive Configuration
NC GPIO
XTAL2B (P4.2)
EXTERNAL
OSCILLATOR
SIGNAL
XTAL1B (P1.0)
GND
6.6
Dual Oscillator Support (AT89LP51ID2)
The AT89LP51ID2 has the ability to switch between two different selectable system clock
sources under software control as shown in Figure 6-2 on page 45.
• OSCA can be a high frequency crystal, external clock or the internal 8 MHz oscillator
• OSCB can be a low frequency crystal, external clock or the internal 8 MHz oscillator
Several operating modes are available and programmable by software:
• Switch system clock source from OSCA to OSCB and vice-versa
• Power down OSCA or OSCB to reduce consumption
• Boot from a fast responding, less accurate oscillator and switch later to a more accurate but
slow to stabilize oscillator.
Selection of which oscillator drives the system clock is controlled by the CKS bit in CKSEL. In
order to switch to a different oscillator, that oscillator must be enabled with the OscAEn or
48
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
OscBEn bits in OSCCON. The oscillator selection at reset is controlled by the Oscillator Select
user fuse (See Section 23.2 on page 192). This fuse is also shadowed in the OSC bit of the
bootloader Hardware Security Byte. The fuse sets the CKS, OscAEn and OscBEn bits as shown
in Table 6-3.
Table 6-3.
Oscillator Reset States
Oscillator Select Fuse
(HSB.OSC)
Control Bit
6.6.1
00H (0)
FFH (1)
OscAEn (OSCCON.0)
0
1
OscBEn (OSSCON.1)
1
0
CKS (CKSEL.0)
0
1
Normal Operation
Only a single oscillator source can drive the system clock at any one time. Under normal conditions it is always possible to dynamically switch from OSCA to OSCB or vice-versa by changing
the CKS bit. The procedure is as follows:
1. Enable the desired oscillator by setting the OscAEn or OscBEn bits in OSCCON
2. Wait for the oscillator to stabilize. This can be a very long time when using the 32 kHz
oscillator. The application software must ensure that the delay is long enough for the
operating conditions
3. Change CKS to switch the system clock source. This takes at most 2 periods of each
oscillator
4. Disable the previous oscillator by clearing the OscAEn or OscBEn bits in OSCCON
5. Note that unlike AT89C51ID2, the OSCB source is affected by both X2 and the CKRL
divider. When changing the clock source, the X2 and CKRL values may need to be
updated to achieve the desired frequency
The clock system hardware will prevent the disabling of the current active oscillator and will prevent switching to a disabled oscillator. However, the hardware will not prevent switching to an
oscillator before it has stabilized. The application software must ensure enough delay between
enabling an oscillator and switching to that oscillator so that the oscillator source can stabilize.
This is generally only an issue when using one of the crystal oscillators.
6.6.2
Idle Operation
Any enabled oscillator will continue to function during Idle mode. Power can be reduced by disabling the alternate oscillator before entering Idle mode. Once in Idle mode, the oscillator source
cannot be changed until the mode is exited. An interrupt exit from Idle will leave the oscillator
control bits (OscAEn, OscBEn and CKS) unchanged. Any reset will exit Idle mode and place
these bits in their default states as determined by the user fuse.
6.6.3
Power-down Operation
All oscillators are stopped during Power-down mode. Once in Power-down mode, the oscillator
source cannot be changed until the mode is exited. An interrupt exit from Power-down will leave
the oscillator control bits (OscAEn, OscBEn and CKS) unchanged. Any reset will exit Powerdown mode and place these bits in their default states as determined by the user fuse.
49
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
6.6.4
Registers
Table 6-4.
CKSEL – Clock Selection Register
CKSEL = 85H (AT89LP51ID2 Only)
Reset Value = XXXX XXX?B
Not Bit Addressable
Bit
Symbol
–
–
–
–
–
–
–
CKS
7
6
5
4
3
2
1
0
Function
CKS
Clock Select. Clear CKS to connect the system clock (CPU and peripherals) to the OSCB source. Set CKS to connect
the system clock to the OSCA source. The default state is set by the Oscillator Select user fuse. See Section 23.2 on
page 192.
Table 6-5.
OSCCON – Oscillator Control Register
OSCCON = 86H (AT89LP51ID2 Only)
Reset Value = XXXX X0??B
Not Bit Addressable
Bit
Symbol
–
–
–
–
–
SCLKT0
OscBEn
OscAEn
7
6
5
4
3
2
1
0
Function
SCLKT0
Sub Clock Timer 0. Clear to connect the Timer 0 counter input to T0 (P3.4). Set to connect the Timer 0 counter input to
OSCB output divided by 128. OSCB must be sourced from crystal oscillator B to use this feature.
OscBEn
OSCB Enable. Clear to power down the OSCB source. Set to enable the OSCB source. The default state is set by the
Oscillator Select user fuse. See Section 23.2 on page 192. OscBEn cannot be disabled when CKS = 0. Disabling OSCB
will free the XTAL1B and XTAL2B pins for use as P1.0 and P4.2.
OscAEn
OSCA Enable. Clear to power down the OSCA source. Set to enable the OSCA source. The default state is set by the
Oscillator Select user fuse. See Section 23.2 on page 192. OscAEn cannot be disabled when CKS = 1.
6.7
X1/X2 Feature
The AT89LP51RD2/ED2/ID2 includes the X1/X2 feature for compatibility with the existing
AT89C51RD2/ED2/ID2. This feature allows a divider-by-2 to be switched in/out between the
oscillator source and the main system clock. This feature is controlled by the X2 bit in CKCON0
(See Table 6-9 on page 52). When X2 = 0 the system clock is divided by two from the oscillator
source, ensuring a 50% duty cycle regardless of the cyclic ratio at the oscillator output. When
X2 = 1 the oscillator output is passed through with no division. In this case the duty cycle at the
oscillator must be between 40% and 60%. Note that the naming convention can be confusing
since X1 means divide-by-2 and X2 means divide-by-1 as shown in Table 6-7. The default state
of the X2 bit is set by the X2 User fuse (See Section 23.2 on page 192) but can always be
changed by software. This fuse is also shadowed in the X2 bit of the bootloader Hardware Security Byte (HSB). Note that the fuse/HSB bit is inverted from the control bit in the CKCON0 SFR.
Table 6-6.
X2
(CKCON0.0)
CPU Clock
XTAL1
Duty Cycle
X2 Fuse
(HSB.X2)
X1
0
fCPU = fSYS/2
No limits
FFH (1)
X2
1
fCPU = fSYS/1
40–60%
00H (0)
Mode
50
X1/X2 Modes
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
6.8
System Clock Prescaler
The AT89LP51RD2/ED2/ID2 includes an 8-bit prescaler that allows the system clock to be
divided down from the selected clock source by even numbers in the range 4–1020 in X1 mode
and 2–510 in X2 mode. The prescaler can reduce power consumption by decreasing the operational frequency during non-critical periods. The prescaler is implemented as an 8-bit counter
with reload. Upon overflow from FFH to 00H the counter is reloaded with the value of the CKRL
register. When CKRL = FFH the prescaler is disabled. The resulting system frequency is given
by the following equations where fOSC is the frequency of the selected clock source and X2 is the
value of CKCON0.0:
X2
f OSC  2
f SYS = --------------------------------------------4   255 – CKRL 
 CKRL  255 
X2
f OSC  2
f SYS = ----------------------------2
 CKRL = 255 
The clock divider will prescale the clock for the CPU and all peripherals. The value of CKRL may
be changed at any time without interrupting normal execution. Changes to CKRL will take affect
on the next prescaler overflow. When CKRL is updated, the new frequency will take affect within
a maximum period of 1024 x tOSC. The prescaler is disabled by reset.
Table 6-7.
CKRL – Clock Reload Register
CKRL = 97H
Reset Value = 1111 1111B
Not Bit Addressable
Bit
Symbol
CKRL7-0
Table 6-8.
CKRL7
CKRL6
CKRL5
CKRL4
CKRL3
CKRL2
CKRL1
CKRL0
7
6
5
4
3
2
1
0
Function
Clock Reload. CKRL holds the reload value for the 8-bit system clock prescaler. When CKRL = FFH the prescaler is
disabled and no division is used. For all other values, the prescaler counts up to FFH and is reloaded with the value of
CKRL on the overflow to 00H. Each overflow of the prescaler will toggle the system clock. Changes to CKRL will take
affect on the next overflow.
CLKREG – Clock Register
CLKREG = AEH
Reset Value = 0101 XXXXB
Not Bit Addressable
Bit
Symbol
TPS3-0
TPS3
TPS2
TPS1
TPS0
—
—
—
—
7
6
5
4
3
2
1
0
Function
Timer Prescaler. The Timer Prescaler selects the time base for Timer 0, Timer 1, Timer 2, PCA and the Watchdog
Timer. The prescaler is implemented as a 4-bit binary down counter. When the counter reaches zero it is reloaded with
the value stored in the TPS bits to give a division ratio between 1 and 16. By default TPS is set to 5 for counting every six
cycles (AT89C51RD2/ED2/ID2 compatibility). The prescaler is always enabled in Compatibility mode. In Fast mode the
prescaler is off by default and can be individually enabled for the peripherals through the CKCON0 and CKCON1 SFRs.
51
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
6.9
Peripheral Clocks
The base peripheral clock is the same as the CPU clock. It is affected by both the X2 setting and
the CKRL prescaler. However, individual peripherals can have their clock further modified using
the Timer Prescaler in the CLKREG register and the clock selection bits in the CKCON0 and
CKCON1 registers. The Timer Prescaler is a 4-bit prescaler controlled by the TPS bits in
CLKREG (See Table 6-8 on page 51). This prescaler is shared among all peripherals and controls the counting rate of Timer 0, Timer 1, Timer 2, the PCA Timer and the Watchdog. By default
the timers will count every CPU clock cycle in Fast mode (TPS = 0000B) and every six CPU
cycles in Compatibility mode (TPS = 0101B).
The bits in CKCON0 and CKCON1 select how the Timer Prescaler affects each peripheral. In
Compatibility mode these bits decide if a further divide-by-two is included in addition to the prescaler. This allows a device in X2 mode to use peripherals that still run in X1 mode, i.e. X2 can be
enabled to speed up the CPU without needing to update the peripheral baud rates, overflow
periods, etc. Peripherals not affected by the Timer Prescaler switch between the CPU clock and
the CPU clock divided-by-2.
In Fast Mode the bits in CKCON0 and CKCON1 turn the Timer Prescaler on/off for each peripheral. The following equations show the peripheral clock rates in Compatibility Mode and Fast
Mode where ?X2 is a peripherals bit in CKCON0 or CKCON1.
f CPU
Compatibility Mode
f PERIPHERAL = ------------------------------------------?X2
2
  TPS + 1 
f CPU
Fast Mode and ?X2 = 1
f PERIPHERAL = -------------------TPS + 1
An overview of the peripheral clock selection is given in Figure 6-7 on page 53. Note that unlike
AT89C51RD2/ED2/ID2, not all the clock selection bits in CKCON0/1 depend on the X2 setting.
Table 6-9.
CKCON0 – Clock Control Register 0
CKCON0 = 8FH
Reset Value = 0000 000?B
Not Bit Addressable
Bit
Symbol
TWIX2
WDX2
PCAX2
52
TWIX2
WDX2
PCAX2
SIX2
T2X2
T1X2
T0X2
X2
7
6
5
4
3
2
1
0
Function
Two-Wire Clock. In Compatibility Mode, clear for one system clock period per peripheral clock cycle and set for two
clock periods per peripheral clock cycle (only valid when X2 = 1). In Fast Mode, clear for one system clock period and
set for TPS+1 clocks per peripheral clock cycle. This bit only affects the generated SCL rate during TWI master mode.
Watchdog Clock. In Compatibility Mode, clear for TPS+1 system clock periods per peripheral clock cycle and set for
2(TPS+1) clock periods per peripheral clock cycle. In Fast Mode, clear for one system clock period and set for TPS+1
clocks per peripheral clock cycle. This bit affects the watchdog timeout period.
Programmable Counter Array Clock. This bit affects the PCA timer increment rate and depends on CPS in CMOD.
CPS1-0 = 00B: In Compatibility Mode, clear for TPS+1 system clock periods per peripheral clock cycle and set for
2(TPS+1) clock periods per peripheral clock cycle. In Fast Mode, clear for one system clock period and set for TPS+1
clocks per peripheral clock cycle.
CPS1-0 = 01B: In Compatibility Mode, clear for one system clock period per peripheral clock cycle and set for two clock
periods per peripheral clock cycle. In Fast Mode, clear for one system clock period and set for TPS+1 clocks per
peripheral clock cycle.
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Symbol
Function
SIX2
UART Clock. In Compatibility Mode, clear for one system clock period per peripheral clock cycle and set for two clock
periods per peripheral clock cycle (only valid when X2 = 1). In Fast Mode, clear for one system clock period and set for
TPS+1 clocks per peripheral clock cycle. This bit affects the generated baud rate during modes 0 and 2.
T2X2
Timer 2 Clock. In Compatibility Mode, clear for TPS+1 system clock periods per peripheral clock cycle and set for
2(TPS+1) clock periods per peripheral clock cycle. In Fast Mode, clear for one system clock period and set for TPS+1
clocks per peripheral clock cycle. This bit affects the timer increment/decrement rate.
T1X2
Timer 1 Clock. In Compatibility Mode, clear for TPS+1 system clock periods per peripheral clock cycle and set for
2(TPS+1) clock periods per peripheral clock cycle. In Fast Mode, clear for one system clock period and set for TPS+1
clocks per peripheral clock cycle. This bit affects the timer increment rate.
T0X2
Timer 0 Clock. In Compatibility Mode, clear for TPS+1 system clock periods per peripheral clock cycle and set for
2(TPS+1) clock periods per peripheral clock cycle. In Fast Mode, clear for one system clock period and set for TPS+1
clocks per peripheral clock cycle. This bit affects the timer increment rate.
X2
CPU Clock. In Compatibility Mode, clear for 12 clock periods per machine cycle and set for 6 clock periods per machine
cycle. In Fast Mode, clear for two clock periods per instruction cycle and set for one clock periods per instruction cycle.
The default state of X2 is set by the X2 Fuse. See Section 23.2 on page 192.
Figure 6-7.
Peripheral Clock Selection
Compatibility Mode
Fast Mode
T0X2
SYSTEM CLOCK
÷(TPS+1)
÷2
T0X2
1
SYSTEM CLOCK
÷(TPS+1)
1
Timer 0
Timer 0
0
0
T1X2
T1X2
1
1
Timer 1
Timer 1
0
0
T2X2
T2X2
1
1
Timer 2
(Reload/Capt)
0
Timer 2
(Reload/Capt)
0
WDX2
WDX2
1
1
Watchdog
Watchdog
0
0
PCAX2
PCAX2
1
1
PCA
(CPS = 00B)
0
PCAX2
÷2
PCAX2
1
÷2
PCA
(CPS = 01B)
0
PCA
(CPS = 00B)
0
1
PCA
(CPS = 01B)
0
SIX2 & X2
SIX2
1
1
UART
0
UART
0
SPIX2 & X2
1
SPIX2
1
SPI
0
SPI
0
TWIX2 & X2
1
TWIX2
1
TWI
0
TWI
0
T2X2
T2X2
1
0
1
Timer 2
(Baud/Clockout)
0
Timer 2
(Baud/Clockout)
53
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 6-10.
CKCON1 – Clock Control Register 1
CKCON1 = AFH
Reset Value = XXXX XXX0B
Not Bit Addressable
Bit
Symbol
SPIX2
6.10
–
–
–
–
–
–
–
SPIX2
7
6
5
4
3
2
1
0
Function
SPI Clock. In Compatibility Mode, clear for one system clock period per peripheral clock cycle and set for two clock
periods per peripheral clock cycle (only valid when X2 = 1). In Fast Mode, clear for one system clock period and set for
TPS+1 clocks per peripheral clock cycle. This bit only affects the generated SCK rate during SPI master mode.
Timer Subclock (AT89L51ID2)
When OSCB of AT89LP51ID2 is enabled and sourced from the low-frequency crystal oscillator,
it can drive the counter input of Timer 0 in place of the T0 pin by setting the SCLKT0 bit in OSCCON. The counter input will be toggled at the oscillator frequency divided by 128. For this mode
to function correctly, the timer peripheral clock must be running (not in Power-down) and operating at a frequency at least twice as high as the subclock as shown in the following equation:
Timer 0 Subclock:
f XTAL1B
f TIMER0  -------------------64
This requirement is due to the fact that the timer must still sample the subclock edges the same
as if were sampling the T0 pin. This feature is not available when OSCB is sourced from either
the external clock on XTAL1B or the internal oscillator.
Pin T2 is also shared with the XTAL1B pin. When OSBC is enabled in the crystal oscillator or
external clock modes, T2 will toggle at the oscillator frequency. Timer 2 can then use the oscillator as its counter input as well, with no division. For this mode to function correctly, the timer
peripheral clock must be running (not in Power-down) and operating at a frequency at least
twice as high OSCB as shown in the following equation:
Timer 2 Subclock:
54
f TIMER2  f XTAL1B  2
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
7. Reset
During reset, all I/O Registers are set to their initial values, the port pins are set to their default
mode, and the program starts execution from the Reset Vector, 0000H. The
AT89LP51RD2/ED2/ID2 has six sources of reset: power-on reset, brown-out reset, external
reset, hardware watchdog reset, PCA watchdog reset and software reset.
Figure 7-1.
Reset Subsystem Diagram
Software
Reset
Hardware
Watchdog
Internal Reset
PCA
Watchdog
POR
BOD
DISRTO
RST
7.1
Power-on Reset
A Power-on Reset (POR) is generated by an on-chip detection circuit. The detection level VPOR
is nominally 1.4V. The POR is activated whenever VDD is below the detection level. The POR circuit can be used to trigger the start-up reset or to detect a major supply voltage failure. The POR
circuit ensures that the device is reset from power-on. A power-on sequence is shown in Figure
7-2. When VDD reaches the Power-on Reset threshold voltage VPOR, an initialization sequence
lasting tPOR is started. When the initialization sequence completes, the start-up timer determines
how long the device is kept in POR after VDD rise. The start-up timer does not begin counting
until after VDD reaches the Brown-out Detector (BOD) threshold voltage VBOD. The POR signal is
activated again, without any delay, when VDD falls below the POR threshold level. A Power-on
Reset (i.e. a cold reset) will set the POF flag in PCON. The internally generated reset can be
extended beyond the power-on period by holding the RST pin active longer than the time-out.
The start-up timer delay is user-configurable with the Start-up Time User Fuses and depends on
the clock source (Table 7-1). The Start-Up Time fuses also control the length of the start-up time
after a Brown-out Reset or when waking up from Power-down during internally timed mode. The
start-up delay should be selected to provide enough settling time for VDD and the selected clock
source. The device operating environment (supply voltage, frequency, temperature, etc.) must
meet the minimum system requirements before the device exits reset and starts normal operation. The RST pin may be held active externally until these conditions are met.
While the POR is active a reset output pulse will be generated on the RST pin to reset the boardlevel circuitry. The output pulse is either open-drain or open-source as shown in Figure 7-4. In
order to properly propagate this pulse to the rest of the board in the case of an external capacitor
or power-supply supervisor circuit, a 1 k resistor should be placed in series with any external
driving circuitry as shown in Figure 7-5. The POR output pulse cannot be disabled.
55
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 7-2.
Power-on Reset Sequence
VBOD
VDD
Time-out
VPOR
tSUT
tPOR
(POL Tied to VCC)
POL
RST
output
VIL
output
input
(RST left unconnected)
Internal
Reset
RST
Internal
Reset
Note:
(RST extended
externally)
tRHD
tPOR is approximately 143 µs ± 5%.
Table 7-1.
Start-up Timer Settings
SUT Fuse 1
SUT Fuse 0
0
0
Clock Source
Internal RC/External Clock
0
1
1
7.2
VIL
tSUT (± 5%) µs
16
Crystal Oscillator
1024
Internal RC/External Clock
512
Crystal Oscillator
2048
Internal RC/External Clock
1024
Crystal Oscillator
4096
Internal RC/External Clock
4096
Crystal Oscillator
16384
1
0
1
Brown-out Reset
The AT89LP51RD2/ED2/ID2 has an on-chip Brown-out Detection (BOD) circuit for monitoring
the VDD level during operation by comparing it to a fixed trigger level. The trigger level VBOD for
the BOD is nominally 2.0V. The purpose of the BOD is to ensure that if VDD fails or dips while
executing at speed, the system will gracefully enter reset without the possibility of errors induced
by incorrect execution. A BOD sequence is shown in Figure 7-3. When VDD decreases to a value
below the trigger level VBOD, the internal reset is immediately activated. When VDD increases
above the trigger level plus about 200 mV of hysteresis, the start-up timer releases the internal
reset after the specified time-out period has expired (Table 7-1).
The BOD generates a reset output pulse.
56
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 7-3.
VDD
Brown-out Detector Reset
VBOD
VPOR
tSUT
Time-out
Internal
Reset
The AT89LP51RD2/ED2/ID2 allows for a wide VDD operating range. The on-chip BOD may not
be sufficient to prevent incorrect execution if VBOD is lower than the minimum required VDD
range, such as when a 5.0V supply is coupled with high frequency operation. In such cases an
external Brown-out Reset circuit connected to the RST pin may be required.
7.3
External Reset
The RST pin of the AT89LP51RD2/ED2/ID2 can function as either an active-low reset input or
as an active-high reset input. The polarity of the RST pin is selectable using the POL pin (formerly EA). When POL is high the RST pin is active high with an on-chip pull-down resistor tied to
GND. When POL is low the RST pin is active low with an on-chip pull-up resistor tied to VDD. The
RST pin structure is shown in Figure 7-4. Entry into reset is completely asynchronous. The presence of the active reset level on the input will immediately reset the device. A glitch filter will
suppress all reset input pulses of less than 50 ns. Exit from reset is synchronous. In Compatibility mode the reset pin is sampled every six clock cycles and must be held inactive for at least
twelve clock cycles to deassert the internal reset. In Fast mode the reset pin is sampled every
clock cycle and must be held inactive for at least two clock cycles to deassert the internal reset.
The AT89LP51RD2/ED2/ID2 includes an on-chip Power-On Reset and Brown-out Detector circuit that ensures that the device is reset from system power up. In most cases a RC startup
circuit is not required on the RST pin, reducing system cost, and the RST pin may be left unconnected if a board-level reset is not present.
Note:
RST also serves as the In-System Programming (ISP) enable. ISP is enabled when the external
reset pin is held active. When ISP is disabled by fuse, ISP may only be entered by pulling RST
active during power-up. If this behavior is necessary, it is recommended to use an active-low reset
so that ISP can be entered by shorting RST to GND at power-up.
Figure 7-4.
Reset Pin Structure
VCC
VCC
POL = 1
POL = 0
DISRTO
WDT Reset
Internal Reset
RST
RST
Internal Reset
DISRTO
WDT Reset
57
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
7.4
Hardware Watchdog Reset
When the Hardware Watchdog times out, it will generate a reset pulse lasting 49 clock cycles.
By default this pulse is also output on the RST pin. The output pulse is either open-drain or
open-source as shown in Figure 7-4. In order to properly propagate this pulse to the rest of the
board in the case of an external capacitor or power-supply supervisor circuit, a 1 k resistor
should be placed in series with any external driving circuitry as shown in Figure 7-5. To disable
the RST output the DISRTO bit in the WDTPRG register must be set to one. Watchdog reset will
set the WDTOVF flag in WDTPRG. To prevent a Watchdog reset, the watchdog reset sequence
1EH/E1H must be written to WDTRST before the Watchdog times out. See Section 15. on page
108 for details on the operation of the Watchdog.
Figure 7-5.
Recommended Reset Output Schematics
Vcc
POL = 1
+
Vcc
1 kΩ
POL = 0
Vcc
RST
RST
1 kΩ
AT89LP51xD2
RST
AT89LP51xD2
RST
+
To other
on-board
circuitry
7.5
To other
on-board
circuitry
PCA Watchdog Reset
Module 4 of the Programmable Counter Array (PCA) can be configured as a watchdog timer.
When a compare match occurs between module 4 and the PCA timer, it will generate an internal
reset pulse lasting 16 clock cycles. This pulse is never output on the RST pin. See Section 14.7
on page 108 for details on the operation of the PCA Watchdog.
7.6
Software Reset
The CPU may generate a 49-clock cycle reset pulse by writing the software reset sequence
5AH/A5H to the WDRST register. A software reset will set the SWRST bit in WDTPRG. See
“Software Reset” on page 109 for more information on software reset. Writing any sequences
other than 5AH/A5H or 1EH/E1H to WDTRST will generate an immediate reset and set both
WDTOVF and SWRST to flag an error. Software reset will also drive the RST pin active unless
DISRTO is set.
7.7
Bootloader Vector
Two conditions can force the AT89LP51RD2/ED2/ID2 to reset to the Bootloader Vector (F800H)
instead of the standard reset vector (0000H).
• The Bootloader Jump Bit Fuse (BLJB) is 00H (See Section 23.2 on page 192)
• The P4.5/PSEN pin is pulled low while RST is deactivated
The Bootloader Vector contains ROM code for the UART-based bootloader. For more information see Section 23.5 “Bootloader” on page 202. To ensure normal start-up, the PSEN pin
should not be tied to ground during power-on.
58
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
8. Power Saving Modes
The AT89LP51RD2/ED2/ID2 supports two different software selectable power-reducing modes:
Idle and Power-down. These modes are accessed through the PCON register. Additional steps
may be required to achieve the lowest possible power consumption while using these modes. In
addition the AT89LP51RD2/ED2/ID2 has fusible configuration options that can further reduce
the active power consumption under certain circumstances.
8.1
Idle Mode
Setting the IDL bit in PCON enters idle mode. Idle mode halts the internal CPU clock. The CPU
state is preserved in its entirety, including the RAM, stack pointer, program counter, program
status word, and accumulator. The Port pins hold the logic states they had at the time that Idle
was activated. Idle mode leaves the peripherals running in order to allow them to wake up the
CPU when an interrupt is generated. The timer and UART peripherals continue to function during Idle. If these functions are not needed during idle, they should be explicitly disabled by
clearing the appropriate control bits in their respective SFRs. The watchdog may be selectively
enabled or disabled during Idle by setting/clearing the WDIDLE bit. The Brown-out Detector is
always active during Idle. Any enabled interrupt source or reset may terminate Idle mode. When
exiting Idle mode with an interrupt, the interrupt will immediately be serviced, and following RETI
the next instruction to be executed will be the one following the instruction that put the device
into Idle.
The power consumption during Idle mode can be further reduced by prescaling down the system
clock using the System Clock Prescaler (Section 6.8 on page 51). Be aware that the clock
divider will affect all peripheral functions and baud rates may need to be adjusted to maintain
their rate with the new clock frequency.
.
Table 8-1.
PCON – Power Control Register
PCON = 87H
Reset Value = 000X 0000B
Not Bit Addressable
Bit
SMOD1
SMOD0
PWDEX
POF
GF1
GF0
PD
IDL
7
6
5
4
3
2
1
0
Symbol
Function
SMOD1
Double Baud Rate bit. Doubles the baud rate of the UART in Modes 1, 2, or 3.
SMOD0
Frame Error Select. When SMOD0 = 1, SCON.7 is SM0. When SMOD0 = 1, SCON.7 is FE. Note that FE will be set after
a frame error regardless of the state of SMOD0.
PWDEX
Power-down Exit Mode. When PWDEX = 0, wake up from Power-down is externally controlled. When PWDEX = 1, wake
up from Power-down is internally timed.
POF
Power Off Flag. POF is set to “1” during power up (i.e. cold reset). It can be set or reset under software control and is not
affected by RST or BOD (i.e. warm resets).
GF1, GF0
General-purpose Flags
PD
Power-down bit. Setting this bit activates power-down operation. The PD bit is cleared automatically by hardware when
waking up from power-down.
IDL
Idle Mode bit. Setting this bit activates Idle mode operation. The IDL bit is cleared automatically by hardware when
waking up from idle
59
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
8.2
Power-down Mode
Setting the Power-down (PD) bit in PCON enters Power-down mode. Power-down mode stops
the oscillator, disables the BOD and powers down the Flash memory in order to minimize power
consumption. Only the power-on circuitry will continue to draw power during Power-down. During Power-down, the power supply voltage may be reduced to the RAM keep-alive voltage. The
RAM contents will be retained, but the SFR contents are not guaranteed once VDD has been
reduced. Power-down may be exited by external reset, power-on reset, or certain enabled
interrupts.
8.2.1
Interrupt Recovery from Power-down
Three external interrupt sources may be configured to terminate Power-down mode: external
interrupts INT0 (P3.2) and INT1 (P3.3), or any Keyboard pin on Port 1. To wake up by external
interrupt INT0 or INT1, that interrupt must be enabled by setting EX0 or EX1 in IEN0 and must
be configured for level-sensitive operation by clearing IT0 or IT1. To wakeup by keyboard interrupt, that interrupt must be enabled by setting EKBD in IEN1 and the individual pin interrupts
must be enabled in the KBE register.
When terminating Power-down by an interrupt, two different wake-up modes are available.
When PWDEX in PCON is one, the wake-up period is internally timed as shown in Figure 8-1. At
the falling edge on the interrupt pin, Power-down is exited, the oscillator is restarted, and an
internal timer begins counting. The internal clock will not be allowed to propagate to the CPU
until after the timer has timed out. After the time-out period the interrupt service routine will
begin. The time-out period is controlled by the Start-up Timer Fuses (see Table 7-1 on page 56).
The interrupt pin need not remain low for the entire time-out period.
Figure 8-1.
Interrupt Recovery from Power-down (PWDEX = 1)
PWD
XTAL1
tSUT
INT1
Internal
Clock
When PWDEX = “0”, the wake-up period is controlled externally by the interrupt. Again, at the
falling edge on the interrupt pin, power-down is exited and the oscillator is restarted. However,
the internal clock will not propagate until the rising edge of the interrupt pin as shown in Figure 82. The interrupt pin should be held low long enough for the selected clock source to stabilize.
After the rising edge on the pin the interrupt service routine will be executed.
60
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 8-2.
Interrupt Recovery from Power-down (PWDEX = 0)
PWD
XTAL1
INT1
Internal
Clock
8.2.2
Reset Recovery from Power-down
The wake-up from Power-down through an external reset is similar to the interrupt with
PWDEX = “1”. At the rising edge of RST, Power-down is exited, the oscillator is restarted, and
an internal timer begins counting as shown in Figure 8-3. The internal clock will not be allowed to
propagate to the CPU until after the timer has timed out. The time-out period is controlled by the
Start-up Timer Fuses. (See Table 7-1 on page 56). If RST returns low before the time-out, a two
clock cycle internal reset is generated when the internal clock restarts. Otherwise, the device will
remain in reset until RST is brought low.
Figure 8-3.
Reset Recovery from Power-down (POL = 1)
PWD
XTAL1
tSUT
RST
Internal
Clock
Internal
Reset
8.3
Reducing Power Consumption
Several possibilities need consideration when trying to reduce the power consumption in an
8051-based system.
• Idle or Power-down mode should be used as often as possible with interrupts waking up the
system to handle specific tasks
• All un-needed peripheral functions should be disabled
• The System Clock Prescaler can scale down the operating frequency during periods of low
demand (See “System Clock Prescaler” on page 51.)
• The ALE output can be disabled by setting AO in AUXR, thereby also reducing EMI
• Write to the EEPROM by page instead of by byte to limit the number of write cycles
• For AT89LP51ID2, switch the system clock from a high power oscillator like XTALA to a lower
power oscillator like the internal 8 MHz oscillator during periods when frequency accuracy is
not as important.
61
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
8.4
Low Power Configuration
Several of the nonvolatile User Configuration Fuses can enable modes where less power will be
consumed during normal operation as listed in Table 8-2. These fuses must generally be set
once by an external programmer to match the desired operating environment.
Table 8-2.
User Configuration Fuses Affecting Power Consumption
Fuse Name
Description
Clock Source A
The Low Power Crystal Oscillator (setting 2) will use half the
power of the High Speed Crystal Oscillator (setting 3) for the
same frequency (  12 MHz)
X2 Mode
X2 mode can keep the same CPU speed while cutting the
crystal frequency in half.
Low Power Mode
Low Power Mode can reduce the power consumption for
system frequencies under 20 MHz. Extra Low Power Mode
can further reduce the power if the system frequency is less
than 1 MHz.
• For crystal frequencies of 12 MHz or less, OSCA should be placed in Low Power Crystal
Oscillator mode
• X1 Mode is supported for compatibility with existing applications. X2 Mode should be used to
achieve the same CPU and peripheral speed at half the crystal frequency
• The Low Power Mode settings change the slope and intercept of the active current versus
frequency relationship. See Table 8-3 below.
Table 8-3.
Fuse 1
(0EH)
Fuse 0
(0DH)
00H (0)
FFH (1)
FFH (1)
—
62
Low Power Mode Fuses
FFH (0)
00H (0)
Mode
Description
Extra Low
Power
Lowest power mode. Use only if the oscillator frequency can
never be above 1 MHz.
Low Power
Low power mode will reduce consumption for CPU frequencies
under 10 MHz and slightly increase consumption for CPU
frequencies over 10 MHz compared to Normal Mode. This
mode is best for oscillator frequencies below 10 MHz or for
frequencies 10–20 MHz where the prescaler may be used to
scale the CPU frequency below 10 MHz.
Normal
Normal mode has higher consumption than Low Power mode
for CPU frequencies under 10 MHz but slightly less
consumption for CPU frequencies over 10 MHz. This mode is
best for oscillator frequencies over 20 MHz or for frequencies
10–20 MHz where the prescaler is not used to scale the CPU
frequency.
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
9. Interrupts
The AT89LP51RD2/ED2/ID2 provides 11 interrupt vectors: two external interrupts (INT0 and
INT1), three timer interrupts (Timers 0, 1 and 2), a serial port interrupt, an SPI interrupt, a keyboard interrupt, a PCA interrupt, an analog comparator interrupt and an ADC interrupt. These
interrupts and the system reset each have a separate program vector at the start of the program
memory space.
Table 9-1.
Polling
Priority
Interrupt Vector Addresses and Priority
Vector
Address
Interrupt
Source
0
System Reset
RST or POR or BOD
0000H
1
External Interrupt 0
IE0
0003H
2
Timer 0 Overflow
TF0
000BH
3
External Interrupt 1
IE1
0013H
4
Timer 1 Overflow
TF1
001BH
6
Serial Port Interrupt
RI or TI
0023H
7
Timer 2 Interrupt
TF2 or EXF2
002BH
5
PCA Interrupt
CF, CCF0, CCF1, CCF2, CCF3 or CCF4
0033H
8
Keyboard Interrupt
KBF7-0
003BH
9
Two-Wire Interrupt
SI
0043H
10
SPI Interrupt
SPIF or MODF or TXE
004BH
11
reserved
12
Analog Comparator Interrupt
CFA or CFB
005BH
13
ADC Interrupt
ADIF
0063H
0053H
Each interrupt source can be individually enabled or disabled by setting or clearing a bit in the
interrupt enable registers: IEN0 and IEN1. The IEN0 register also contains a global disable bit,
EA, which disables all interrupts. All of the bits that generate interrupts can be set or cleared by
software, with the same result as though they had been set or cleared by hardware. That is,
interrupts can be generated and pending interrupts can be canceled in software.
9.1
Interrupt Priority
Each interrupt source can be individually programmed to one of four priority levels by setting or
clearing bits in the interrupt priority registers: IPL0, IPL1, IPH0 and IPH1. IPL0 and IPL1 hold the
low order priority bits and IPH0 and IPH1 hold the high priority bits for each interrupt as shown in
Table 9-2. An interrupt service routine in progress can be interrupted by a higher priority interrupt, but not by another interrupt of the same or lower priority. The highest priority interrupt
cannot be interrupted by any other interrupt source. If two requests of different priority levels are
pending at the end of an instruction, the request of higher priority level is serviced. If requests of
the same priority level are pending at the end of an instruction, an internal polling sequence
determines which request is serviced. The polling sequence is based on the vector address; an
interrupt with a lower vector address has higher priority than an interrupt with a higher vector
address, except in the case of the PCA, whose polling priority is moved up by two as shown in
Table 9-1 and Figure 9-1. Note that the polling sequence is only used to resolve pending
requests of the same priority level.
63
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 9-2.
Figure 9-1.
Priority Level Bit Values
IPH.x
IPL.x
Interrupt Priority Level
0
0
0 (Lowest)
0
1
1
1
0
2
1
1
3 (Highest)
Interrupt Control Subsystem
IPHx, IPLx
High Priority
Interrupt
IEN1, IEN0
IT0
EX0
EA
3
INT0
IE0
ET0
EA
0
3
EX1
EA
0
3
ET1
EA
0
3
EC
EA
0
3
ES
EA
0
3
ET2
EA
0
3
EKBD
EA
0
3
ETWI
EA
0
3
ESPI
EA
0
3
ECMP
EA
0
3
EADC
EA
0
3
TF0
IT1
INT1
IE1
TF1
Interrupt Polling
Sequence,
Decreasing from
High to Low
Priority
PCA IT
RI
TI
TF2
EXF2
KBD IT
TWIF
SPIF
TXE
MODF
CFA
CFB
ADIF
0
Individual Enable
64
Global Disable
Low Priority
Interrupt
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
9.2
Interrupt Response
The interrupt flags may be set by their hardware in any clock cycle. The interrupt controller polls
the flags in the last clock cycle of the instruction in progress. If one of the flags was set in the
preceding cycle, the polling cycle will find it and the interrupt system will generate an LCALL to
the appropriate service routine as the next instruction, provided that the interrupt is not blocked
by any of the following conditions:
• An interrupt of equal or higher priority level is already in progress
• The instruction in progress is RETI or any write to the IENx, IPLx or IPHx registers
Each of these conditions will block the generation of the LCALL to the interrupt service routine.
The second condition ensures that if the instruction in progress is RETI or any access to IENx,
IPLx or IPHx, then at least one more instruction will be executed before any interrupt is vectored
to. The polling cycle is repeated at the last cycle of each instruction, and the values polled are
the values that were present at the previous clock cycle. If an active interrupt flag is not being
serviced because of one of the above conditions and is no longer active when the blocking
condition is removed, the denied interrupt will not be serviced. In other words, the fact that the
interrupt flag was once active but not serviced is not remembered. Every polling cycle is new.
If a request is active and conditions are met for it to be acknowledged, a hardware subroutine
call to the requested service routine will be the next instruction executed. The call itself takes
four cycles. Thus, a minimum of five complete clock cycles elapsed between activation of an
interrupt request and the beginning of execution of the first instruction of the service routine. A
longer response time results if the request is blocked by one of the previously listed conditions. If
an interrupt of equal or higher priority level is already in progress, the additional wait time
depends on the nature of the other interrupt's service routine. If the instruction in progress is not
in its final clock cycle, the additional wait time cannot be more than 4 cycles, since the longest
instruction is 5 cycles long. If the instruction in progress is RETI, the additional wait time cannot
be more than 9 cycles (a maximum of 4 more cycles to complete the instruction in progress, plus
a maximum of 5 cycles to complete the next instruction). Thus, in a single-interrupt system, the
response time is always more than 5 clock cycles and less than 14 clock cycles. See Figure 9-2
and Figure 9-3.
When an interrupt is serviced, its interrupt flag must be cleared before the RETI instruction or
else the interrupt will continue to be generated. Many interrupt vectors have multiple sources.
The service routine normally must determine which flag bit generated the interrupt and that bit
must be cleared by software. If multiple source bits are set for one interrupt, the interrupt will
continue to be generated until all the source bits have been cleared. In some cases the interrupt
flags is cleared by hardware when the interrupt is acknowledged.
The External Interrupts INT0 and INT1 can each be either level-activated or edge-activated,
depending on bits IT0 and IT1 in Register TCON. The flags that actually generate these interrupts are the IE0 and IE1 bits in TCON. When the service routine is vectored to, hardware clears
the flag that generated an external interrupt only if the interrupt was edge-activated. If the interrupt was level activated, then the external requesting source (rather than the on-chip hardware)
controls the request flag. The Timer 0 and Timer 1 Interrupts are generated by TF0 and TF1,
which are set by a rollover in their respective Timers). When a timer interrupt is generated, the
on-chip hardware clears the flag that generated it when the service routine is vectored to. All
other flags must be cleared by software.
65
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 9-2.
Minimum Interrupt Response Time (Fast Mode)
Clock Cycles
1
5
INT0
IE0
Instruction
Figure 9-3.
Ack.
Cur. Instr.
LCALL
1st ISR Instr.
Maximum Interrupt Response Time (Fast Mode)
Clock Cycles
1
5
10
14
INT0
Ack.
IE0
Instruction
Figure 9-4.
RETI
MOVX @/DPTR, A
LCALL
1st ISR Instr.
Minimum Interrupt Response Time (Compatibility Mode)
Clock Cycles
1
INT0
14
Ack.
IE0
Instruction
Figure 9-5.
LCALL
ISR
Maximum Interrupt Response Time (Compatibility Mode)
Clock Cycles
1
13
37
49
INT0
Ack.
IE0
Instruction
66
RETI
MUL AB
LCALL
ISR
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
9.3
Interrupt Registers
Table 9-3.
IEN0 – Interrupt Enable Register 0
IEN0 = A8H
Reset Value = 0000 0000B
Bit Addressable
Bit
EA
EC
ET2
ES
ET1
EX1
ET0
EX0
7
6
5
4
3
2
1
0
Symbol
Function
EA
Global Interrupt Enable
All interrupts are disabled when EA = 0. When EA = 1, each interrupt source is enabled/disabled by setting /clearing its own enable bit.
EC
PCA Interrupt Enable
Clear to disable the PCA interrupt. Set to enable the PCA interrupt when EA = 1.
ET2
Timer 2 Interrupt Enable
Clear to disable the Timer 2 interrupt. Set to enable the Timer 2 interrupt when EA = 1.
ES
Serial Port Interrupt Enable
Clear to disable the UART interrupt. Set to enable the UART interrupt when EA = 1.
ET1
Timer 1 Interrupt Enable
Clear to disable the Timer 1 interrupt. Set to enable the Timer 1 interrupt when EA = 1.
EX1
External Interrupt 1 Enable.
Clear to disable the INT1 interrupt. Set to enable the INT1 interrupt when EA = 1.
ET0
Timer 0 Interrupt Enable
Clear to disable the Timer 0 interrupt. Set to enable the Timer 0 interrupt when EA = 1.
EX0
External Interrupt 0 Enable
Clear to disable the INT0 interrupt. Set to enable the INT0 interrupt when EA = 1.
Table 9-4.
IEN1 – Interrupt Enable Register 1
IEN1 = B1H
Reset Value = 0000 0000B
Bit Addressable
Bit
–
–
EADC
ECMP
–
ESPI
ETWI
EKBD
7
6
5
4
3
2
1
0
Symbol
Function
EADC
ADC Interrupt Enable.
Clear to disable the ADC interrupt. Set to enable the ADC interrupt when EA = 1.
ECMP
Analog COmparator Interrupt Enable
Clear to disable the Analog Comparator interrupt. Set to enable the Analog Comparator interrupt when EA = 1.
ESPI
SPI Interrupt Enable
Clear to disable the SPI interrupt. Set to enable the SPI interrupt when EA = 1.
ETWI
TWI Interrupt Enable
Clear to disable the TWI interrupt. Set to enable the TWI interrupt when EA = 1.
EKBD
Keyboard Interrupt Enable
Clear to disable the Keyboard interrupt. Set to enable the Keyboard interrupt when EA = 1.
67
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 9-5.
IPL0 – Interrupt Priority Low Register 0
IPL0 = B8H
Reset Value = 0000 0000B
Bit Addressable
IP0DIS
PPCL
PT2L
PSL
PT1L
PX1L
PT0L
PX0L
7
6
5
4
3
2
1
0
Bit
Symbol
Function
IP0DIS
Interrupt Level 0 Disable
Clear to enable all interrupts with priority level 0. Set to disable all interrupts with priority level 0.
PPCL
PCA Interrupt Priority Low
Low order bit for PCA interrupt priority level.
PT2L
Timer 2 Interrupt Priority Low
Low order bit for Timer 2 interrupt priority level.
PSL
Serial Port Interrupt Priority Low
Low order bit for UART interrupt priority level.
PT1L
Timer 1 Interrupt Priority Low
Low order bit for Timer 1 interrupt priority level.
PX1L
External Interrupt 1 Priority Low
Low order bit for INT1 interrupt priority level.
PT0L
Timer 0 Interrupt Priority Low
Low order bit for Timer 0 interrupt priority level.
PX0L
External Interrupt 0 Priority Low
Low order bit for INT0 interrupt priority level.
Table 9-6.
IPL1 – Interrupt Priority Low Register 1
IPL1 = B2H
Reset Value = 0000 0000B
Bit Addressable
Bit
IP2DIS
–
PADCL
PCMPL
–
PSPL
PTWL
PKBL
7
6
5
4
3
2
1
0
Symbol
Function
IP2DIS
Interrupt Level 2 Disable
Clear to enable all interrupts with priority level 2. Set to disable all interrupts with priority level 2.
PADCL
ADC Interrupt Priority Low
Low order bit for ADC interrupt priority level.
PCMPL
Analog Comparator Interrupt Priority Low
Low order bit for Analog Comparator interrupt priority level.
PSPL
SPI Interrupt Priority Low
Low order bit for SPI interrupt priority level.
PTWL
TWI Interrupt Priority Low
Low order bit for TWI interrupt priority level.
PKBL
Keyboard Interrupt Priority Low
Low order bit for Keyboard interrupt priority level.
68
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 9-7.
IPH0 – Interrupt Priority High Register 0
IPH0 = B7H
Reset Value = 0000 0000B
Not Bit Addressable
IP1DIS
PPCH
PT2H
PSH
PT1H
PX1H
PT0H
PX0H
7
6
5
4
3
2
1
0
Bit
Symbol
Function
IP1DIS
Interrupt Level 1 Disable
Clear to enable all interrupts with priority level 1. Set to disable all interrupts with priority level 1.
PPCH
PCA Interrupt Priority High
High order bit for PCA interrupt priority level.
PT2H
Timer 2 Interrupt Priority High
High order bit for Timer 2 interrupt priority level.
PSH
Serial Port Interrupt Priority High
High order bit for UART interrupt priority level.
PT1H
Timer 1 Interrupt Priority High
High order bit for Timer 1 interrupt priority level.
PX1H
External Interrupt 1 Priority High
High order bit for INT1 interrupt priority level.
PT0H
Timer 0 Interrupt Priority High
High order bit for Timer 0 interrupt priority level.
PX0H
External Interrupt 0 Priority High
High order bit for INT0 interrupt priority level.
Table 9-8.
IPH1 – Interrupt Priority High Register 1
IPH1 = B3H
Reset Value = 0000 0000B
Not Bit Addressable
Bit
IP3DIS
–
PADCH
PCMPH
–
PSPH
PTWH
PKBH
7
6
5
4
3
2
1
0
Symbol
Function
IP3DIS
Interrupt Level 3 Disable
Clear to enable all interrupts with priority level 3. Set to disable all interrupts with priority level 3.
PADCH
ADC Interrupt Priority High
High order bit for ADC interrupt priority level.
PCMPH
Analog Comparator Interrupt Priority High
High order bit for Analog Comparator interrupt priority level.
PSPH
SPI Interrupt Priority High
High order bit for SPI interrupt priority level.
PTWH
TWI Interrupt Priority High
High order bit for TWI interrupt priority level.
PKBH
Keyboard Interrupt Priority High
High order bit for Keyboard interrupt priority level.
69
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
10. External Interrupts
The INT0 (P3.2) and INT1 (P3.3) pins of the AT89LP51RD2/ED2/ID2 may be used as external
interrupt sources. The external interrupts can be programmed to be level-activated or transitionactivated by setting or clearing bit IT1 or IT0 in Register TCON. If ITx = 0, external interrupt x is
triggered by a detected low at the INTx pin. If ITx = 1, external interrupt x is edge-triggered. In
this mode if successive samples of the INTx pin show a high in one cycle and a low in the next
cycle, interrupt request flag IEx in TCON is set. Flag bit IEx then requests the interrupt.
Since the external interrupt pins are sampled once each clock cycle, an input high or low should
hold for at least 2 system periods to ensure sampling. If the external interrupt is transition-activated, the external source has to hold the request pin high for at least two clock cycles, and then
hold it low for at least two clock cycles to ensure that the transition is seen so that interrupt
request flag IEx will be set. IEx will be automatically cleared by the CPU when the service routine is called if generated in edge-triggered mode. If the external interrupt is level-activated, the
external source has to hold the request active until the requested interrupt is actually generated.
Then the external source must deactivate the request before the interrupt service routine is completed, or else another interrupt will be generated. Both INT0 and INT1 may wake up the device
from the Power-down state.
Other peripheral pins can also generate interrupts in response to an external event:
• A negative edge on the T2EX pin (P1.1) can set the EXF2 flag in T2CON
• Transitions on the PCA capture inputs CEX0–CEX4 (P1.3–7) can set the CCFx bits in CCON
• Transitions or levels on Port 1 can set the bits in KBF using the keyboard interface (see next
section).
11. Keyboard Interface and General-purpose Interrupts
The AT89LP51RD2/ED2/ID2 implements a keyboard interface allowing the connection of a 1 x n
to 8 x n matrix keyboard. The keyboard function provides 8 configurable external interrupts on
Port 1. Each port pin can detect high/low levels or positive/negative edges. The keyboard inputs
are considered as 8 independent interrupt sources sharing the same interrupt vector. The KBE
register selects which bits of Port 1 are enabled to generate an interrupt. The KBMOD and KBLS
registers determine the mode for each individual pin. KBMOD selects between level-sensitive
and edge-triggered mode. KBLS selects between high/low in level mode and positive/negative in
edge mode. A block diagram is shown in Figure 11-1.
The pins of Port 1 are sampled every clock cycle. In level-sensitive mode, a valid level must
appear in two successive samples before generating the interrupt. In edge-triggered mode, a
transition will be detected if the value changes from one sample to the next. When an interrupt
condition on a pin is detected, and that pin is enabled, the appropriate flag in the KBF register is
set. The flags in KBF must be cleared by software. Any enabled keyboard interrupt may wake up
the device from the Idle or Power-down state.
Unlike AT89C51RD2/ED2/ID2 the flags in KBF are not cleared by reading the register. The software may clear each bit individually or all at once. This allows the interface to be used for
general purpose external interrupts where some flags can be left pending between calls to the
service routine. Each flag can also be made pending by software by writing a one to it. To
achieve the same behavior as AT89C51RD2/ED2/ID2, the service routine must clear the entire
register.
70
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 11-1. Keyboard Block Diagram
KBLS
1
7
KBMOD
1
7
KBE
KBF
7
7
D Q
(P1.7) GPI7
0
1
0
6
1
6
6
6
D Q
(P1.6) GPI6
0
1
0
5
1
5
5
5
D Q
(P1.5) GPI5
0
1
0
4
1
4
4
4
D Q
(P1.4) GPI4
Interrupt
0
1
0
3
1
3
3
3
D Q
(P1.3) GPI3
0
1
0
2
1
2
2
2
D Q
(P1.2) GPI2
0
1
0
1
1
1
1
1
D Q
(P1.1) GPI1
0
1
0
0
1
0
0
0
D Q
(P1.0) GPI0
0
0
CLK
71
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
11.1
Registers
.
Table 11-1.
KBMOD – Keyboard Mode Register
KBMOD = 9FH
Reset Value = 0000 0000B
Not Bit Addressable
KBMOD7
KBMOD6
KBMOD5
KBMOD4
KBMOD3
KBMOD2
KBMOD1
KBMOD0
7
6
5
4
3
2
1
0
Bit
KBMOD.x
0 = level-sensitive interrupt for P1.x
1 = edge-triggered interrupt for P1.x
Table 11-2.
KBLS – Keyboard Level Select Register
KBLS = 9CH
Reset Value = 0000 0000B
Not Bit Addressable
KBLS7
KBLS6
KBLS5
KBLS4
KBLS3
KBLS2
KBLS1
KBLS0
7
6
5
4
3
2
1
0
Bit
KBLS.x
0 = detect low level or negative edge on P1.x
1 = detect high level or positive edge on P1.x
.
Table 11-3.
KBE – Keyboard Interrupt Enable Register
KBE = 9DH
Reset Value = 0000 0000B
Not Bit Addressable
Bit
KBE7
KBE6
KBE5
KBE4
KBE3
KBE2
KBE1
KBE0
7
6
5
4
3
2
1
0
KBE.x
0 = interrupt for P1.x disabled
1 = interrupt for P1.x enabled
.
Table 11-4.
KBF – Keyboard Interrupt Flag Register
KBF = 9EH
Reset Value = 0000 0000B
Not Bit Addressable
Bit
KBF7
KBF6
KBF5
KBF4
KBF3
KBF2
KBF1
KBF0
7
6
5
4
3
2
1
0
KBF.x
0 = interrupt on P1.x inactive
1 = interrupt on P1.x active. Must be cleared by software.
72
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
I/O Ports
The AT89LP51RD2/ED2/ID2 can be configured for between 36 and 40 I/O pins. The exact number of general I/O pins available depends on the clock and external memory configuration as
shown in Table 11-5.
Table 11-5.
AT89LP51RD2/ED2 I/O Pin Configurations
Clock Source A
External Program Access
External Data Access
Number of I/O
Pins
Yes (RD+WR)
18
No
20
8-bit (ALE+RD+WR+P0)
27
16-bit (ALE+RD+WR+P0)
19
No
38
Yes (RD+WR)
19
No
21
8-bit (ALE+RD+WR+P0)
28
16-bit (ALE+RD+WR+P0+P2)
20
No
39
Yes (RD+WR)
20
No
22
8-bit (ALE+RD+WR+P0)
29
16-bit (ALE+RD+WR+P0+P2)
21
No
40
Yes (PSEN+ALE+P0+P2)
External Crystal or
Resonator
No
Yes (PSEN+ALE+P0+P2)
External Clock
No
Yes (PSEN+ALE+P0+P2)
Internal RC
Oscillator
No
Note:
11.2
On AT89LP51ID2 OSCB requires 0, 1 or 2 I/O pins depending on the Clock Source B setting. Disabling OSCB (OscbEn = 0) frees up the OSCB pins for general use. Disabling OSCA
(OscAEn = 0) does NOT free up the OSCA pins. OSCA must be configured for Internal RC mode
to use these pins even when running from OSCB only.
Port Configuration
All port pins on the AT89LP51RD2/ED2/ID2 may be configured in one of four modes: quasi-bidirectional (standard 8051 port outputs), push-pull output, open-drain output, or input-only. Port
modes may be assigned in software on a pin-by-pin basis as shown in Table 11-6 using the registers listed in Table 11-7. The Tristate-Port User Fuse (See Section 23.2 on page 192)
determines the default state of the port pins. When the fuse is enabled, all port pins on P1, P2
and P3 default to input-only mode after reset. When the fuse is disabled, all port pins on P1, P2
and P3 default to quasi-bidirectional mode after reset and are weakly pulled high. P0 always
defaults to open-drain mode. P4.4–5 always default to quasi-bidirectional mode. P4.0–1 always
default to open-drain. The other pins of P4 obey the fuse.
Each port pin also has a Schmitt-triggered input for improved input noise rejection. During
Power-down all the Schmitt-triggered inputs are disabled with the exception of P3.2 (INT0), P3.3
(INT1), RST, P4.6 (XTAL1) and P4.7 (XTAL2). Therefore, P3.2, P3.3, P4.6 and P4.7 should not
be left floating during Power-down. n addition any pin of Port 1 configured as a keyboard interrupt input will also remain active during Power-down to wake-up the device. These interrupt pins
should either be disabled before entering Power-down or they should not be left floating.
73
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
.
Table 11-6.
PxM0.y
PxM1.y
0
0
Quasi-bidirectional
0
1
Push-pull Output
1
0
Input Only (High Impedance)
1
1
Open-Drain Output
.
Table 11-7.
Port Mode
Port Configuration Registers
Port
Port Data
Port Configuration
0
P0 (80H)
P0M0 (D4H), P0M1 (D5H)
1
P1 (90H)
P1M0 (E6H), P1M1 (E7H)
2
P2 (A0H)
P2M0 (D6H), P2M1 (D7H)
3
P3 (B0H)
P3M0 (DEH), P3M1 (CFH)
4
P4 (C0H)
P4M0 (BEH), P4M1 (BFH)
.
Table 11-8.
11.2.1
Configuration Modes for Port x Pin y
Port Configuration Reset Values
Register
Tristate Ports Fuse = FFH (1)
Tristate Ports Fuse = 00H (0)
P0M0
FF
FF
P0M1
FF
FF
P1M0
FF
00
P1M1
00
00
P2M0
FF
00
P2M1
00
00
P3M0
FF
00
P3M1
00
00
P4M0
C7
03
P4M0
03
03
Quasi-bidirectional Output
Port pins in quasi-bidirectional output mode function similar to standard 8051 port pins. A Quasibidirectional port can be used both as an input and output without the need to reconfigure the
port. This is possible because when the port outputs a logic high, it is weakly driven, allowing an
external device to pull the pin low. When the pin is driven low, it is driven strongly and able to
sink a large current. There are three pull-up transistors in the quasi-bidirectional output that
serve different purposes.
One of these pull-ups, called the “very weak” pull-up, is turned on whenever the port latch for the
pin contains a logic “1”. This very weak pull-up sources a very small current that will pull the pin
high if it is left floating. When the pin is pulled low externally this pull-up will always source some
current. The very weak pull-up is disabled when the port register contains a zero. In addition the
very weak pull-ups of all quasi-bidirectional ports can be disabled globally by setting the DPU bit
in the AUXR register (See Table 3-3 on page 19).
74
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
A second pull-up, called the “weak” pull-up, is turned on when the port latch for the pin contains
a logic “1” and the pin itself is also at a logic “1” level. This pull-up provides the primary source
current for a quasi-bidirectional pin that is outputting a “1”. If this pin is pulled low by an external
device, this weak pull-up turns off, and only the very weak pull-up remains on. In order to pull the
pin low under these conditions, the external device has to sink enough current to overpower the
weak pull-up and pull the port pin below its input threshold voltage.
The third pull-up is referred to as the “strong” pull-up. This pull-up is used to speed up low-tohigh transitions on a quasi-bidirectional port pin when the port latch changes from a logic “0” to a
logic “1”. When this occurs, the strong pull-up turns on for one CPU clock, quickly pulling the port
pin high. The quasi-bidirectional port configuration is shown in Figure 11-3.
Figure 11-2. Quasi-bidirectional Output
1 Clock Delay
(D Flip-Flop)
VCC
VCC
VCC
Strong
Very
Weak
Weak
Port
Pin
From Port
Register
Input
Data
PWD
11.2.2
Input-only Mode
The input only port configuration is shown in Figure 11-3. The output drivers are tristated. The
input includes a Schmitt-triggered input for improved input noise rejection. The input circuitry of
P3.2, P3.3, P4.6 and P4.7 is not disabled during Power-down (see Figure 11-4) and therefore
these pins should not be left floating during Power-down when configured in this mode.
Input-only mode can reduce power consumption for low-level inputs over quasi-bidirectional
mode because the “very weak” pull-up is turned off and only very small leakage current in the
sub microamp range is present.
Figure 11-3. Input Only
Input
Data
Port
Pin
PWD
Figure 11-4. Input Circuit for P3.2, P3.3, P4.6 and P4.7
Input
Data
Port
Pin
75
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
11.2.3
Open-drain Output
The open-drain output configuration turns off all pull-ups and only drives the pull-down transistor
of the port pin when the port latch contains a logic “0”. To be used as a logic output, a port configured in this manner must have an external pull-up, typically a resistor tied to VDD. The pulldown for this mode is the same as for the quasi-bidirectional mode. The open-drain port configuration is shown in Figure 11-5. The input circuitry of P3.2, P3.3, P4.6 and P4.7 is not disabled
during Power-down (see Figure 11-4) and therefore these pins should not be left floating during
Power-down when configured in this mode.
Figure 11-5. Open-Drain Output
Port
Pin
From Port
Register
Input
Data
PWD
11.2.4
Push-pull Output
The push-pull output configuration has the same pull-down structure as both the open-drain and
the quasi-bidirectional output modes, but provides a continuous strong pull-up when the port
latch contains a logic “1”. The push-pull mode may be used when more source current is needed
from a port output. The push-pull port configuration is shown in Figure 11-6.
Figure 11-6. Push-pull Output
VCC
Port
Pin
From Port
Register
Input
Data
PWD
11.3
Port Analog Functions
The AT89LP51RD2/ED2/ID2 incorporates two analog comparators and an 8-channel analog-todigital converter. In order to give the best analog performance and minimize power consumption, pins that are being used for analog functions must have both their digital outputs and digital
inputs disabled. Digital outputs are disabled by putting the port pins into the input-only mode as
described in “Port Configuration” on page 73. The analog input pins will always default to inputonly mode after reset regardless of the state of the Tristate-Port Fuse.
76
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Digital inputs on P2.4, P2.5, P2.6 and P2.7 are disabled whenever an analog comparator is
enabled by setting the CENA or CENB bits in ACSRA and ACSRB and that pin is configured for
input-only mode. To use an analog input pin as a high-impedance digital input while a comparator is enabled, that pin should be configured in open-drain mode and the corresponding port
register bit should be set to 1.
Digital inputs on Port 0 are disabled for each pin configured for input-only mode whenever the
ADC is enabled by setting the ADCE bit and clearing the DAC bit in DADC. To use any Port 0
input pin as a high-impedance digital input while the ADC is enabled, that pin should be configured in open-drain mode and the corresponding port register bit should be set to 1. When DAC
mode is enabled, P2.2 and P2.3 are forced to input-only mode.
11.4
Port Read-Modify-Write
A read from a port will read either the state of the pins or the state of the port register depending
on which instruction is used. Simple read instructions will always access the port pins directly.
Read-modify-write instructions, which read a value, possibly modify it, and then write it back, will
always access the port register. This includes bit write instructions such as CLR or SETB as they
actually read the entire port, modify a single bit, then write the data back to the entire port. See
Table 11-9 for a complete list of Read-Modify-Write instruction which may access the ports.
Table 11-9.
11.5
Port Read-Modify-Write Instructions
Mnemonic
Instruction
Example
ANL
Logical AND
ANL P1, A
ORL
Logical OR
ORL P1, A
XRL
Logical EX-OR
XRL P1, A
JBC
Jump if bit set and clear bit
JBC P3.0, LABEL
CPL
Complement bit
CPL P3.1
INC
Increment
INC P1
DEC
Decrement
DEC P3
DJNZ
Decrement and jump if not zero
DJNZ P3, LABEL
MOV PX.Y, C
Move carry to bit Y of Port X
MOV P1.0, C
CLR PX.Y
Clear bit Y of Port X
CLR P1.1
SETB PX.Y
Set bit Y of Port X
SETB P3.2
Port Alternate Functions
Most general-purpose digital I/O pins of the AT89LP51RD2/ED2/ID2 share functionality with the
various I/Os needed for the peripheral units. Table 11-11 lists the alternate functions of the port
pins. Alternate functions are connected to the pins in a logic AND fashion. In order to enable the
alternate function on a port pin, that pin must have a “1” in its corresponding port register bit,
otherwise the input/output will always be “0”. However, alternate functions may be temporarily
forced to “0” by clearing the associated port bit, provided that the pin is not in input-only mode.
Furthermore, each pin must be configured for the correct input/output mode as required by its
peripheral before it may be used as such. Table 11-10 shows how to configure a generic pin for
use with an alternate function.
77
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 11-10. Pin Function Configurations for Port x Pin y
PxM0.y
PxM1.y
Px.y
I/O Mode
0
0
1
bidirectional (internal pull-up)
0
1
1
output
1
0
X
input
1
1
1
bidirectional (external pull-up)
Table 11-11. Port Pin Alternate Functions
Configuration Bits
Port Pin
PxM0.y
PxM1.y
P0.0
P0M0.0
P0M1.0
P0.1
P0M0.1
P0M1.1
P0.2
P0M0.2
P0M1.2
P0.3
P0M0.3
P0M1.3
P0.4
P0M0.4
P0M1.4
P0.5
P0M0.5
P0M1.5
P0.6
P0M0.6
P0M1.6
P0.7
P0M0.7
P0M1.7
Alternate
Function
AD0
ADC0
AD1
ADC1
AD2
ADC2
AD3
ADC3
AD4
ADC4
AD5
ADC5
AD6
ADC6
AD7
ADC7
T2
P1.0
P1M0.0
P1M1.0
GPI0
Notes
Automatic configuration
input-only
Automatic configuration
input-only
Automatic configuration
input-only
Automatic configuration
input-only
Automatic configuration
input-only
Automatic configuration
input-only
Automatic configuration
input-only
Automatic configuration
input-only
OSCB must be disabled or in
internal oscillator mode
(AT89LP51ID2)
XTAL1B
T2EX
P1.1
P1M0.1
P1M1.1
SS
REMAP = 0
GPI1
78
P1.2
P1M0.2
P1M1.2
P1.3
P1M0.3
P1M1.3
ECI
GPI2
CEX0
GPI3
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 11-11. Port Pin Alternate Functions
Configuration Bits
Port Pin
PxM0.y
PxM1.y
Alternate
Function
SS
P1.4
P1M0.4
P1M1.4
Notes
REMAP = 1
GPI4
CEX1
P1.5
P1M0.5
P1M1.5
MISO
REMAP = 0
MOSI
REMAP = 1
CEX2
GPI5
P1.6
P1M0.6
P1M1.6
SCK
REMAP = 0
MISO
REMAP = 1
CEX3
GPI6
P1.7
P1M0.7
P1M1.7
MOSI
REMAP = 0
SCK
REMAP = 1
CEX4
GPI7
P2.0
P2M0.0
P2M1.0
A8
P2.1
P2M0.1
P2M1.1
A9
P2.2
P2M0.2
P2M1.2
P2.3
P2M0.3
P2M1.3
P2.4
P2M0.4
P2M1.4
P2.5
P2M0.5
P2M1.5
P2.6
P2M0.6
P2M1.6
P2.7
P2M0.7
P2M1.7
P3.0
P3M0.0
P3M1.0
RXD
P3.1
P3M0.1
P3M1.1
TXD
P3.2
P3M0.2
P3M1.2
INT0
P3.3
P3M0.3
P3M1.3
INT1
P3.4
P3M0.4
P3M1.4
T0
P3.5
P3M0.5
P3M1.5
T1
P3.6
P3M0.6
P3M1.6
WR
A10
DA+
input-only
A11
DA-
input-only
A12
AIN0
input-only
A13
AIN1
input-only
A14
AIN2
input-only
A15
AIN3
input-only
79
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 11-11. Port Pin Alternate Functions
Configuration Bits
80
Port Pin
PxM0.y
PxM1.y
Alternate
Function
P3.7
P3M0.7
P3M1.7
RD
P4.0
P4M0.0
P4M1.0
SCL
open-drain
P4.1
P4M0.1
P4M1.1
SDA
open-drain
P4.2
P4M0.2
P4M1.2
XTAL2B
P4.4
P4M0.4
P4M1.4
ALE
P4.5
P4M0.5
P4M1.5
PSEN
P4.6
P4M0.6
P4M1.6
XTAL1A
OSCA must be set to internal RC
mode to use P4.6
P4.7
P4M0.7
P4M1.7
XTAL2A
OSCA must be set to internal RC
or external clock modes to use
P4.7
Notes
OSCB must be disabled or in
internal oscillator or external clock
modes to use P4.2(AT89LP51ID2)
Set AO in AUXR to use P4.4
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
12. Enhanced Timer 0 and Timer 1 with PWM
The AT89LP51RD2/ED2/ID2 has two 16-bit Timer/Counters, Timer 0 and Timer 1, with the following features:
• Two 16-bit timer/counters with 16-bit reload registers
• Two independent 8-bit precision PWM outputs with 8-bit prescalers
• UART or SPI baud rate generation using Timer 1
• Output pin toggle on timer overflow
• Split timer mode allows for three separate timers (2 8-bit, 1 16-bit)
• Gated modes allow timers to run/halt based on an external input
Timer 0 and Timer 1 have similar modes of operation. As timers, the timer registers normally
increase every clock cycle. Thus, the registers count clock cycles. The timer rate can be prescaled by a value between 1 and 16 using the Timer Prescaler (see Section 6.9 on page 52).
Both Timers share the same prescaler. In Compatibility mode the prescaler is always enabled
and TPS defaults to 5, so the timers count every six clock cycles (1/12 of the oscillator frequency
in X1 mode or 1/6 of the oscillator frequency in X2 mode). In X2 mode the timers can be set to
the X1 rate by setting the T0X2 or T1X2 bits in CKCON1. In Fast mode the prescaler is not
enabled by default so the count rate is equal to the system frequency (1/2 of the oscillator frequency in X1 mode or equal to the oscillator frequency in X2 mode). In this case setting the
T0X2 or T1X2 bits in CKCON1 enables the prescaler for each timer.
f SYS
Compatibility Mode
f TIMER = ---------------------------------------------TnX2
2
  TPS + 1 
f SYS
f TIMER = -------------------Fast Mode and TnX2 = 1
TPS + 1
Fast Mode and TnX2 = 0
f TIMER = f SYS
As counters, the timer registers are incremented in response to a 1-to-0 transition at the corresponding input pins, T0 or T1. In Fast mode the external input is sampled every clock cycle.
When the samples show a high in one cycle and a low in the next cycle, the count is incremented. The new count value appears in the register during the cycle following the one in which
the transition was detected. Since 2 clock cycles are required to recognize a 1-to-0 transition,
the maximum count rate is 1/2 of the system frequency. There are no restrictions on the duty
cycle of the input signal, but it should be held for at least one full clock cycle to ensure that a
given level is sampled at least once before it changes.
In Compatibility mode the counter input sampling is controlled by the prescaler. Since TPS
defaults to 6 in this mode, the pins are sampled every six system clocks. Therefore the input signal should be held for at least six clock cycles to ensure that a given level is sampled at least
once before it changes.
Furthermore, the Timer or Counter functions for Timer 0 and Timer 1 have four operating modes:
13-bit timer, 16-bit timer, 8-bit auto-reload timer, and split timer. The control bits C/T in the Special Function Register TMOD select the Timer or Counter function. The bit pairs (M1, M0) in
TMOD select the operating modes.
81
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
12.1
Registers
Table 12-1 lists the registers used by Timer 0/1. TCON, TCONB and TMOD are detailed below.
Table 12-1.
Name
Address
TCON
88H
Control
Y
TMOD
89H
Mode
N
TL0
8AH
Timer 0 low-byte
N
TL1
8BH
Timer 1 low-byte
N
TH0
8CH
Timer 0 high-byte
N
TH1
8DH
Timer 1 high-byte
N
TCONB
91H
Mode
N
RL0
F2H
Timer 0 reload low-byte
N
RL1
F3H
Timer 1 reload low-byte
N
RH0
F4H
Timer 0 reload high-byte
N
RH1
F5H
Timer 1 reload high-byte
N
Note:
.
Table 12-2.
Timer 0/1 Register Summary
Purpose
Bit-Addressable
The RHn/RLn registers are not required by the Timer during Modes 0, 2 or 3 and may be used as
temporary storage registers in these modes, except when using the PWM generator.
TCON – Timer/Counter Control Register
TCON = 88H
Reset Value = 0000 0000B
Bit Addressable
Bit
TF1
TR1
TF0
TR0
IE1
IT1
IE0
IT0
7
6
5
4
3
2
1
0
Symbol
Function
TF1
Timer 1 Overflow Flag
Set by hardware on Timer/Counter overflow. Cleared by hardware when the processor vectors to interrupt routine.
TR1
Timer 1 Run Control
Set/cleared by software to turn Timer/Counter on/off.
TF0
Timer 0 Overflow Flag
Set by hardware on Timer/Counter overflow. Cleared by hardware when the processor vectors to interrupt routine.
TR0
Timer 0 Run Control
Set/cleared by software to turn Timer/Counter on/off.
IE1
Interrupt 1 Edge Flag
Set by hardware when external interrupt edge detected. Cleared when interrupt processed.
IT1
Interrupt 1 Type
Set/cleared by software to specify falling edge/low level triggered external interrupts.
IE0
Interrupt 0 Edge Flag
Set by hardware when external interrupt edge detected. Cleared when interrupt processed.
IT0
Interrupt 0 Type
Set/cleared by software to specify falling edge/low level triggered external interrupts.
82
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 12-3.
TMOD – Timer/Counter Mode Control Register
TMOD Address = 089H
Reset Value = 0000 0000B
Not Bit Addressable
Bit
GATE1
C/T1
T1M1
T1M0
GATE0
C/T0
T0M0
T0M1
7
6
5
4
3
2
1
0
Symbol
Function
GATE1
Timer 1 Gating Control
When set, Timer/Counter 1 is enabled only while INT1 pin is high and TR1 control pin is set. When cleared, Timer 1 is
enabled whenever TR1 control bit is set.
C/T1
Timer or Counter Selector 1
Cleared for Timer operation (input from internal system clock). Set for Counter operation (input from T1 input pin). C/T1
must be zero when using Timer 1 in PWM output mode.
T1M1
T1M0
Timer 1 Operating Mode
Mode
T1M1
T1M0
Operation
0
0
0
Variable Timer Mode. 8-bit Timer/Counter TH1 with TL1 as 1–8 bit prescaler. Default
is 5 bits for a 13-bit timer/counter compatible with AT89C51RD2/ED2/ID2.
1
0
1
16-bit Auto-Reload Mode. TH1 and TL1 are cascaded to form a 16-bit Timer/Counter
which is reloaded from RH1 and RL1 when it overflows.
2
1
0
8-bit Auto-Reload Mode. TH1 holds a value which is reloaded into 8-bit Timer/Counter
TL1 each time it overflows.
3
1
1
Timer/Counter 1 is stopped
GATE0
Timer 0 Gating Control
When set, Timer/Counter 0 is enabled only while INT0 pin is high and TR0 control pin is set. When cleared, Timer 0 is
enabled whenever TR0 control bit is set.
C/T0
Timer or Counter Selector 0
Cleared for Timer operation (input from internal system clock). Set for Counter operation (input from T0 input pin). C/T0
must be zero when using Timer 0 in PWM output mode.
T0M1
T0M0
Timer 0 Operating Mode
Mode
T0M1
T0M0
Operation
0
0
0
Variable Timer Mode. 8-bit Timer/Counter TH0 with TL0 as 1–8 bit prescaler. Default
is 5 bits for a 13-bit timer/counter compatible with AT89C51RD2/ED2/ID2.
1
0
1
16-bit Auto-Reload Mode. TH0 and TL0 are cascaded to form a 16-bit Timer/Counter
which is reloaded from RH0 and RL0 when it overflows.
2
1
0
8-bit Auto-Reload Mode. TH0 holds a value which is reloaded into 8-bit Timer/Counter
TL0 each time it overflows.
3
1
1
Split Timer Mode. TL0 is an 8-bit Timer/Counter controlled by the standard Timer 0
control bits. TH0 is only an 8-bit timer controlled by Timer 1 control bits.
83
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 12-4.
TCONB – Timer/Counter Control Register B
TCONB = 91H
Reset Value = 0010 0100B
Not Bit Addressable
Bit
PWM1EN
PWM0EN
PSC12
PSC11
PSC10
PSC02
PSC01
PSC00
7
6
5
4
3
2
1
0
Symbol
Function
PWM1EN
Pulse Width Modulation 1 Enable
Set to configure Timer 1 for Pulse Width Modulation output on T1 (P3.5). Clear to disable T1 as an output.
PWM0EN
Pulse Width Modulation 0 Enable
Set to configure Timer 0 for Pulse Width Modulation output on T0 (P3.4). Clear to disable T0 as an output.
PSC12
PSC11
PSC10
Timer 1 Prescaler
Prescaler for Timer 1 Mode 0. The number of active bits in TL1 equals PSC1 + 1. After reset PSC1 = 100B which
enables 5 bits of TL1 for compatibility with the 13-bit Mode 0 in AT89C51RD2/ED2/ID2.
PSC02
PSC01
PSC00
Timer 0 Prescaler
Prescaler for Timer 0 Mode 0. The number of active bits in TL0 equals PSC0 + 1. After reset PSC0 = 100B which
enables 5 bits of TL0 for compatibility with the 13-bit Mode 0 in AT89C51RD2/ED2/ID2.
12.2
Mode 0 – Variable Width Timer/Counter
Both Timers in Mode 0 are 8-bit Counters with a variable prescaler. The prescaler may vary from
1 to 8 bits depending on the PSC bits in TCONB, giving the timer a range of 9 to 16 bits.
By default the timer is configured as a 13-bit timer compatible to Mode 0 in the standard 8051.
Figure 12-1 shows the Mode 0 operation as it applies to Timer 1 in 13-bit mode. As the count
rolls over from all “1”s to all “0”s, it sets the Timer interrupt flag TF1. The counter input is enabled
to the Timer when TR1 = 1 and either GATE1 = 0 or INT1 = 1. Setting GATE1 = 1 allows the
Timer to be controlled by external input INT1, to facilitate pulse width measurements. TR1 is a
control bit in the TCON register. GATE1 is in TMOD. The 13-bit register consists of all 8 bits of
TH1 and the lower 5 bits of TL1. The upper 3 bits of TL1 are indeterminate and should be
ignored. Setting the run flag (TR1) does not clear the registers.
The following equation gives the timeout period for Mode 0. In Fast Mode, TPS applies only
when the TnX2 bits in CKCON0 are set. TPS always applies in Compatibility Mode, therefore
setting TnX2 in Compatibility Mode will double the timeout period.
PSCn + 1
Mode 0:
256  2
Time-out Period = ----------------------------------------   TPS + 1 
f SYS
Mode 0 operation is the same for Timer 0 as for Timer 1, except that TR0, TF0, GATE0 and
INT0 replace the corresponding Timer 1 signals in Figure 12-1. There are two different C/T bits,
one for Timer 1 (TMOD.6) and one for Timer 0 (TMOD.2).
84
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 12-1. Timer/Counter 1 Mode 0: Variable Width Counter
CLKSYS
TPS
C/T = 0
TL1
(8 Bits)
C/T = 1
T1 Pin
Control
PSC1
TR1
TH1
(8 Bits)
GATE1
TF1
Interrupt
INT1 Pin
12.3
Mode 1 – 16-bit Auto-Reload Timer/Counter
In Mode 1 the Timers are configured for 16-bit auto-reload. The Timer register is run with all
16 bits. The 16-bit reload value is stored in the high and low reload registers (RH1/RL1). The
clock is applied to the combined high and low timer registers (TH1/TL1). As clock pulses are
received, the timer counts up: 0000H, 0001H, 0002H, etc. An overflow occurs on the FFFFH-to0000H transition, upon which the timer register is reloaded with the value from RH1/RL1 and the
overflow flag bit in TCON is set. See Figure 12-2. The reload registers default to 0000H, which
gives the full 16-bit timer period compatible with the standard 8051. Mode 1 operation is the
same for Timer/Counter 0.
The following equation gives the timeout period for Mode 1. In Fast Mode, TPS applies only
when the TnX2 bits in CKCON0 are set. TPS always applies in Compatibility Mode, therefore
setting TnX2 in Compatibility Mode will double the timeout period.
Mode 1:
 65536 – {RHn, RLn} 
Time-out Period = ---------------------------------------------------------   TPS + 1 
f SYS
Figure 12-2. Timer/Counter 1 Mode 1: 16-bit Auto-Reload
RL1
(8 Bits)
CLKSYS
RH1
(8 Bits)
TPS
Reload
C/T = 0
TL1
(8 Bits)
TH1
(8 Bits)
TF1
Interrupt
C/T =1
T1 Pin
Control
TR1
GATE1
INT1 Pin
85
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
12.4
Mode 2 – 8-bit Auto-Reload Timer/Counter
Mode 2 configures the Timer register as an 8-bit Counter (TL1) with automatic reload, as shown
in Figure 12-3. Overflow from TL1 not only sets TF1, but also reloads TL1 with the contents of
TH1, which is preset by software. The reload leaves TH1 unchanged. Mode 2 operation is the
same for Timer/Counter 0.
The following equation gives the timeout period for Mode 2. In Fast Mode, TPS applies only
when the TnX2 bits in CKCON0 are set. TPS always applies in Compatibility Mode, therefore
setting TnX2 in Compatibility Mode will double the timeout period.
 256 – THn 
Time-out Period = --------------------------------   TPS + 1 
f SYS
Mode 2:
Figure 12-3. Timer/Counter 1 Mode 2: 8-bit Auto-Reload
CLKSYS
TPS
C/T = 0
TL1
(8 Bits)
TF1
Interrupt
C/T = 1
Control
T1 Pin
Reload
TR1
TH1
(8 Bits)
GATE1
INT0 Pin
Note:
12.5
RH1/RL1 are not required by Timer 1 during Mode 2 and may be used as temporary storage
registers.
Mode 3 – 8-bit Split Timer
Timer 1 in Mode 3 simply holds its count. The effect is the same as setting TR1 = 0. Timer 0 in
Mode 3 establishes TL0 and TH0 as two separate counters. The logic for Mode 3 on Timer 0 is
shown in Figure 12-4. TL0 uses the Timer 0 control bits: C/T, GATE0, TR0, INT0, and TF0. TH0
is locked into a timer function (counting clock cycles) and takes over the use of TR1 and TF1
from Timer 1. Thus, TH0 now controls the Timer 1 interrupt. While Timer 0 is in Mode 3, Timer 1
will still obey its settings in TMOD but cannot generate an interrupt.
Mode 3 is for applications requiring an extra 8-bit timer or counter. With Timer 0 in Mode 3, the
AT89LP51RD2/ED2/ID2 can appear to have four Timer/Counters. When Timer 0 is in Mode 3,
Timer 1 can be turned on and off by switching it out of and into its own Mode 3. In this case,
Timer 1 can still be used by the serial port as a baud rate generator or in any application not
requiring an interrupt.
The following equation gives the timeout period for Mode 3. In Fast Mode, TPS applies only
when the TnX2 bits in CKCON0 are set. TPS always applies in Compatibility Mode, therefore
setting TnX2 in Compatibility Mode will double the timeout period.
Mode 3:
86
256-   TPS + 1 
Time-out Period = -----------f SYS
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 12-4. Timer/Counter 0 Mode 3: Two 8-bit Counters
CLKSYS
÷TPS
C/T = 0
C/T =1
T0 Pin
(8 Bits)
Interrupt
(8 Bits)
Interrupt
Control
GATE0
INT0 Pin
CLKSYS
÷TPS
Control
12.6
Pulse Width Modulation
On the AT89LP51RD2/ED2/ID2, Timer 0 and Timer 1 may be independently configured as 8-bit
asymmetrical (edge-aligned) pulse width modulators (PWM) by setting the PWM0EN or
PWM1EN bits in TCONB, respectively. In PWM Mode the generated waveform is output on the
timer's input pin, T0 or T1. Therefore, C/Tx must be set to “0” when in PWM mode and the T0
(P3.4) and T1 (P3.5) must be configured in an output mode. The Timer Overflow Flags and
Interrupts will continue to function while in PWM Mode and Timer 1 may still generate the baud
rate for the UART. The timer GATE function also works in PWM mode, allowing the output to be
halted by an external input. Each PWM channel has four modes selected by the mode bits in
TMOD.
An example waveform for Timer 0 in PWM Mode 0 is shown in Figure 12-5. TH0 acts as an 8-bit
counter while RH0 stores the 8-bit compare value. When TH0 is 00H the PWM output is
set high. When the TH0 count reaches the value stored in RH0 the PWM output is set low.
Therefore, the pulse width is proportional to the value in RH0. To prevent glitches, writes to
RH0 only take effect on the FFH to 00H overflow of TH0. Setting RH0 to 00H will keep the PWM
output low.
Figure 12-5. 8-bit Asymmetrical Pulse Width Modulation
TH0
TF0 Set
FFH
RH0
00H
time
(P3.4)T0
87
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
12.6.1
Mode 0 – 8-bit PWM with 8-bit Logarithmic Prescaler
In Mode 0, TLn acts as a logarithmic prescaler driving 8-bit counter THn (see Figure 12-6). The
PSCn bits in TCONB control the prescaler value. On THn overflow, the duty cycle value in RHn
is transferred to OCRn and the output pin is set high. When the count in THn matches OCRn,
the output pin is cleared low. The following formulas give the output frequency and duty cycle for
Timer n in PWM Mode 0. Timer 1 in PWM Mode 0 is identical to Timer 0.
Mode 0:
Note:
f SYS
1
-  --------------------f out = --------------------------------------PSCn + 1 TPS + 1
256  2
RHn
Duty Cycle % = 100  -----------256
In Fast Mode, TPS applies only when the TnX2 bits in CKCON0 are set. TPS always
applies in Compatibility Mode, therefore setting TnX2 in Compatibility Mode will halve
the output frequency.
Figure 12-6. Timer/Counter 1 PWM Mode 0
RH1
(8 Bits)
TL1
(8 Bits)
TPS
CLKSYS
OCR1
Control
=
TR1
T1
PSC1
GATE1
TH1
(8 Bits)
INT1 Pin
12.6.2
Mode 1 – 8-bit PWM with 8-bit Linear Prescaler
In Mode 1, TLn provides linear prescaling with an 8-bit auto-reload from RLn (see Figure 12-7 on
page 89). On TLn overflow, TLn is loaded with the value of RLn. THn acts as an 8-bit counter.
On THn overflow, the duty cycle value in RHn is transferred to OCRn and the output pin is set
high. When the count in THn matches OCRn, the output pin is cleared low. The following formulas give the output frequency and duty cycle for Timer n in PWM Mode 1. Timer 1 in PWM Mode
1 is identical to Timer 0.
Mode 1:
Note:
88
f SYS
1 f out = -----------------------------------------------  -------------------256   256 – RLn  TPS + 1
RHn
Duty Cycle % = 100  -----------256
In Fast Mode, TPS applies only when the TnX2 bits in CKCON0 are set. TPS always
applies in Compatibility Mode, therefore setting TnX2 in Compatibility Mode will halve
the output frequency.
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 12-7. Timer/Counter 1 PWM Mode 1
RH1
(8 Bits)
RL1
(8 Bits)
OCR1
=
T1
TL1
(8 Bits)
TPS
CLKSYS
TH1
(8 Bits)
Control
TR1
GATE1
INT1 Pin
12.6.3
Mode 2 – 8-bit Frequency Generator
Timer n in PWM Mode 2 functions as an 8-bit Auto-Reload timer, the same as normal Mode 2,
with the exception that the output pin Tn is toggled at every TLn overflow (see Figure 12-8 and
Figure 12-9 on page 90). Timer 1 in PWM Mode 2 is identical to Timer 0. PWM Mode 2 can be
used to output a square wave of varying frequency. THn acts as an 8-bit counter. The following
formula gives the output frequency for Timer n in PWM Mode 2.
f SYS
1
Mode 2:
f out = ---------------------------------------- --------------------2   256 – THn  TPS + 1
Note:
In Fast Mode, TPS applies only when the TnX2 bits in CKCON0 are set. TPS always
applies in Compatibility Mode, therefore setting TnX2 in Compatibility Mode will halve
the output frequency.
Figure 12-8. Timer/Counter 1 PWM Mode 2
TH1
(8 Bits)
CLKSYS
TL1
(8 Bits)
TPS
T1
Control
TR1
GATE1
INT1 Pin
89
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 12-9. PWM Mode 2 Waveform
FFh
THx
Tx
12.6.4
Mode 3 – Split 8-bit PWM
Timer 1 in PWM Mode 3 simply holds its count. The effect is the same as setting TR1 = 0.
Timer 0 in PWM Mode 3 establishes TL0 and TH0 as two separate PWM counters in a manner
similar to normal Mode 3. PWM Mode 3 on Timer 0 is shown in Figure 12-10. Only the Timer
Prescaler is available to change the output frequency during PWM Mode 3. TL0 can use the
Timer 0 control bits: GATE, TR0, INT0, PWM0EN and TF0. TH0 is locked into a timer function
and uses TR1, PWM1EN and TF1. RL0 provides the duty cycle for TL0 and RH0 provides the
duty cycle for TH0.
PWM Mode 3 is for applications requiring a single PWM channel and two timers, or two PWM
channels and an extra timer or counter. With Timer 0 in PWM Mode 3, the
AT89LP51RD2/ED2/ID2 can appear to have four Timer/Counters. When Timer 0 is in PWM
Mode 3, Timer 1 can be turned on and off by switching it out of and into its own Mode 3. In this
case, Timer 1 can still be used by the serial port as a baud rate generator or in any application
not requiring an interrupt. The following formulas give the output frequency and duty cycle for
Timer 0 in PWM Mode 3.
f SYS
1
Mode 3:
f out = ------------  --------------------256 TPS + 1
Note:
90
Mode 3, T0:
RL0
Duty Cycle % = 100  ----------256
Mode 3, T1:
RH0
Duty Cycle % = 100  -----------256
In Fast Mode, TPS applies only when the TnX2 bits in CKCON0 are set. TPS always
applies in Compatibility Mode, therefore setting TnX2 in Compatibility Mode will halve
the output frequency.
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 12-10. Timer/Counter 0 PWM Mode 3
RL0
(8 Bits)
OCR0
=
T0
TL0
(8 Bits)
TPS
CLKSYS
Control
RH0
(8 Bits)
TR0
GATE0
OCR1
INT0 Pin
=
T1
TPS
CLKSYS
TH0
(8 Bits)
TR1
13. Timer 2
The AT89LP51RD2/ED2/ID2 includes a 16-bit Timer/Counter 2 with the following features:
• 16-bit timer/counter with one 16-bit reload/capture register
• One external reload/capture input
• Up/Down counting mode with external direction control
• UART baud rate generation
• Output-pin toggle on timer overflow
Timer 2 is a 16-bit Timer/Counter that can operate as either a timer or an event counter. The
type of operation is selected by bit C/T2 in the SFR T2CON. Timer 2 has three operating modes:
capture, auto-reload (up or down counting), and baud rate generator. The modes are selected
by bits in T2CON and T2MOD, as shown in Table 13-1.
Timer 2 consists of two 8-bit registers, TH2 and TL2. In the Timer function, the register is incremented every clock cycle. The timer rate can be prescaled by a value between 1 and 16 using
the Timer Prescaler (see Section 6.9 on page 52). In Compatibility mode the prescaler is always
enabled and TPS defaults to 5, so Timer 2 counts every six clock cycles (1/12 of the oscillator
frequency in X1 mode or 1/6 of the oscillator frequency in X2 mode). In X2 mode Timer 2 can be
set to the X1 rate by setting the T2X2 bit in CKCON1. In Fast mode the prescaler is not enabled
by default so the count rate is equal to the system frequency (1/2 of the oscillator frequency in
X1 mode or equal to the oscillator frequency in X2 mode). In this case setting the T2X2 bit in
CKCON1 enables the prescaler for Timer 2.
Note that Timer 2 is not affected by the prescaler when operating in the Baud-Rate or Frequency
Generator modes.
91
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
f SYS
Compatibility Mode
f TIMER = ---------------------------------------------T2X2
2
  TPS + 1 
f SYS
f TIMER = -------------------Fast Mode and T2X2 = 1
TPS + 1
Fast Mode and T2X2 = 0
f TIMER = f SYS
Note:
In Fast Mode, TPS applies only when the T2X2 bit in CKCON0 is set. TPS always
applies in Compatibility Mode, therefore setting T2X2 in Compatibility Mode will halve
the timer frequency.
In the Counter function, the register is incremented in response to a 1-to-0 transition at its corresponding external input pin, T2. In Fast mode the external input is sampled every clock cycle.
When the samples show a high in one cycle and a low in the next cycle, the count is incremented. The new count value appears in the register during the cycle following the one in which
the transition was detected. Since 2 clock cycles are required to recognize a 1-to-0 transition,
the maximum count rate is 1/2 of the system frequency. There are no restrictions on the duty
cycle of the input signal, but it should be held for at least one full clock cycle to ensure that a
given level is sampled at least once before it changes.
In Compatibility mode the counter input sampling is controlled by the prescaler. Since TPS
defaults to 6 in this mode, the pins are sampled every six system clocks. Therefore the input signal should be held for at least six clock cycles to ensure that a given level is sampled at least
once before it changes.
Table 13-1.
Timer 2 Operating Modes
RCLK + TCLK
CP/RL2
DCEN
T2OE
TR2
MODE
0
0
0
0
1
16-bit Auto-reload
0
0
1
0
1
16-bit Auto-reload Up-Down
0
1
X
0
1
16-bit Capture
1
X
X
X
1
Baud Rate Generator
X
X
X
1
1
Frequency Generator
X
X
X
X
0
(Off)
The following definitions for Timer 2 are used in the subsequent paragraphs:
Table 13-2.
Symbol
Definition
MIN
0000H
MAX
FFFFH
BOTTOM
92
Timer 2 Definitions
16-bit value of {RCAP2H,RCAP2L}
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
13.1
Timer 2 Registers
Control and status bits for Timer 2 are contained in registers T2CON (see Table 13-3) and
T2MOD (see Table 13-4). The register pair {TH2, TL2} at addresses 0CDH and 0CCH are the
16-bit timer register for Timer 2. The register pair {RCAP2H, RCAP2L} at addresses 0CBH and
0CAH are the 16-bit Capture/Reload register for Timer 2 in capture and auto-reload modes.
Table 13-3.
T2CON – Timer/Counter 2 Control Register
T2CON Address = 0C8H
Reset Value = 0000 0000B
Bit Addressable
Bit
TF2
EXF2
RCLK
TCLK
EXEN2
TR2
C/T2
CP/RL2
7
6
5
4
3
2
1
0
Symbol
Function
TF2
Timer 2 Overflow Flag
Set by hardware when Timer 2 overflows and must be cleared by software. TF2 will not be set when either
RCLK = 1 or TCLK = 1. TF2 will generate an interrupt when ET2 is set in IEN0.
EXF2
Timer 2 External Flag
Set when either a capture or reload is caused by a negative transition on T2EX and EXEN2 = 1. When Timer 2 interrupt is
enabled, EXF2 = 1 will cause the CPU to vector to the Timer 2 interrupt routine. EXF2 must be cleared by software. EXF2
does not cause an interrupt in up/down counter mode (DCEN = 1) or dual-slope mode.
RCLK
Receive Clock Enable
Set to use Timer 2 overflow pulses for receive clock in serial port Modes 1 and 3. Clear to use Timer 1 overflows for the
receive clock.
TCLK
Transmit Clock Enable
Set to use Timer 2 overflow pulses for transmit clock in serial port Modes 1 and 3. Clear to use Timer 1 overflows for the
transmit clock.
EXEN2
Timer 2 External Enable
When set, allows a capture or reload to occur as a result of a negative transition on T2EX if Timer 2 is not being used to
clock the serial port. EXEN2 = 0 causes Timer 2 to ignore events at T2EX.
TR2
Timer 2 Run Control
Start/Stop control for Timer 2. TR2 = 1 starts the timer. TR2 = 0 stops the timer.
C/T2
Timer/Counter Select 2
Clear C/T2 = 0 for timer function. Set C/T2 = 1 for external event counter on T2 (P1.0) (falling edge triggered). C/T2 must
be 0 to use clock out mode.
CP/RL2
Capture/Reload Select
CP/RL2 = 1 causes captures to occur on negative transitions at T2EX if EXEN2 = 1. CP/RL2 = 0 causes automatic
reloads to occur when Timer 2 overflows or negative transitions occur at T2EX when EXEN2 = 1. When either RCLK or
TCLK = 1, this bit is ignored and the timer is forced to auto-reload on Timer 2 overflow.
Note:
The Timer 2 operating mode depends on bits in both T2CON and T2MOD as shown in Table 13-1. The RCLK, TCLK and T2OE
bits have priority over CP/RL2.
93
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 13-4.
T2MOD – Timer 2 Mode Control Register
T2MOD Address = 0C9H
Reset Value = 0000 0000B
Not Bit Addressable
Bit
–
–
–
–
–
–
T2OE
DCEN
7
6
5
4
3
2
1
0
Symbol
Function
T2OE
Timer 2 Output Enable
When T2OE = 1 and C/T2 = 0, the T2 pin will toggle after every Timer 2 overflow.
DCEN
Timer 2 Down Count Enable
When Timer 2 operates in Auto-Reload mode and EXEN2 = 1, setting DCEN = 1 will cause Timer 2 to count up or down
depending on the state of T2EX.
13.2
Capture Mode
In the Capture mode, Timer 2 is a fixed 16-bit timer or counter that counts up from MIN to MAX.
An overflow from MAX to MIN sets bit TF2 in T2CON. If EXEN2 = 1, a 1-to-0 transition at external input T2EX also causes the current value in TH2 and TL2 to be captured into RCAP2H and
RCAP2L, respectively. In addition, the transition at T2EX causes bit EXF2 in T2CON to be set.
The EXF2 and TF2 bits can generate an interrupt. Capture mode is illustrated in Figure 13-1.
The Timer 2 overflow rate in Capture mode is given by the following equation:
Capture Mode:
Note:
65536
Time-out Period = ----------------   TPS + 1 
f SYS
In Fast Mode, TPS applies only when the T2X2 bit in CKCON0 is set. TPS always
applies in Compatibility Mode, therefore setting T2X2 in Compatibility Mode will double
the timeout period.
Figure 13-1. Timer 2 Diagram: Capture Mode
CLKSYS
÷TPS
C/T2 = 0
TL2
TH2
TF2
OVERFLOW
C/T2 = 1
TR2
CAPTURE
T2 PIN
RCAP2L
RCAP2H
TRANSITION
DETECTOR
TIMER 2
INTERRUPT
T2EX PIN
EXF2
EXEN2
94
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
13.3
Auto-Reload Mode
Timer 2 can be programmed to count up or down when configured in its 16-bit auto-reload
mode. This feature is invoked by the DCEN (Down Counter Enable) bit located in the SFR
T2MOD (see Table 13-4). Upon reset, the DCEN bit is set to 0 so that timer 2 will default to
count up. When DCEN is set, Timer 2 can count up or down, depending on the value of the
T2EX pin. A summary of the Auto-Reload behaviors is listed in Table 13-5.
Table 13-5.
13.3.1
Summary of Auto-Reload Modes
DCEN
T2EX
Direction
Behavior
0
X
Up
BOTTOM  MAX reload to BOTTOM
1
0
Down
MAX  BOTTOM underflow to MAX
1
1
Up
BOTTOM  MAX overflow to BOTTOM
Up Counter
Figure 13-2 shows Timer 2 automatically counting up when DCEN = 0. In this mode Timer 2
counts up to MAX and then sets the TF2 bit upon overflow. The overflow also causes the timer
registers to be reloaded with BOTTOM, the 16-bit value in RCAP2H and RCAP2L. If EXEN2 = 1,
a 16-bit reload can be triggered either by an overflow or by a 1-to-0 transition at external input
T2EX. This transition also sets the EXF2 bit. Both the TF2 and EXF2 bits can generate an interrupt. The Timer 2 overflow rate for this mode is given in the following equation:
Auto-Reload Mode:
65536 – {RCAP2H , RCAP2L}
Time-out Period = -------------------------------------------------------------------------------   TPS + 1 
f SYS
DCEN = 0
Note:
In Fast Mode, TPS applies only when the T2X2 bit in CKCON0 is set. TPS always
applies in Compatibility Mode, therefore setting T2X2 in Compatibility Mode will double
the timeout period.
Figure 13-2. Timer 2 Diagram: Auto-Reload Mode (DCEN = 0)
CLKSYS
÷TPS
TL2
TH2
95
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 13-3. Timer 2 Waveform: Auto-Reload Mode (DCEN = 0)
TF2 Set
MAX
BOTTOM
MIN
13.3.2
Up or Down Counter
Setting DCEN = 1 enables Timer 2 to count up or down, as shown in Figure 13-5. In this mode,
the T2EX pin controls the direction of the count (if EXEN2 = 1). A logic 1 at T2EX makes Timer 2
count up. When T2CM1-0 = 00B, the timer will overflow at MAX and set the TF2 bit. This overflow
also causes BOTTOM, the 16-bit value in RCAP2H and RCAP2L, to be reloaded into the timer
registers, TH2 and TL2, respectively. A logic 0 at T2EX makes Timer 2 count down. The timer
underflows when TH2 and TL2 equal BOTTOM, the 16-bit value stored in RCAP2H and
RCAP2L. The underflow sets the TF2 bit and causes MAX to be reloaded into the timer registers. The EXF2 bit toggles whenever Timer 2 overflows or underflows and can be used as a 17th
bit of resolution. In this operating mode, EXF2 does not flag an interrupt.
The behavior of Timer 2 when DCEN is enabled is shown in Figure 13-4. The timer overflow/underflow rate for up-down counting mode is the same as for up counting mode, provided
that the count direction does not change. Changes to the count direction may result in longer or
shorter periods between time-outs.
Figure 13-4. Timer 2 Waveform: Auto-Reload Mode (DCEN = 1)
TF2 Set
MAX
BOTTOM
MIN
T2EX
EXF2
96
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 13-5. Timer 2 Diagram: Auto-Reload Mode (DCEN = 1)
CLKSYS
13.4
÷TPS
Baud Rate Generator
Timer 2 is selected as the baud rate generator by setting TCLK and/or RCLK in T2CON (Table
13-3). Note that the baud rates for transmit and receive can be different if Timer 2 is used for the
receiver or transmitter and Timer 1 is used for the other function. Setting RCLK and/or TCLK
puts Timer 2 into its baud rate generator mode, as shown in Figure 13-6.
The baud rate generator mode is similar to the auto-reload mode, in that a rollover in TH2
causes the Timer 2 registers to be reloaded with the 16-bit value in registers RCAP2H and
RCAP2L, which are preset by software.
The baud rates in UART Modes 1 and 3 are determined by Timer 2’s overflow rate according to
the following equation.
2 Overflow RateModes 1 and 3 Baud Rates = Timer
----------------------------------------------------------16
The Timer can be configured for either timer or counter operation. In most applications, it is configured for timer operation (CP/T2 = 0). The baud rate formulas are given below.
f SYS
Modes 1, 3
= --------------------------------------------------------------------------------------------16   65536 –  RCAP2H,RCAP2L  
Baud Rate
where (RCAP2H, RCAP2L) is the content of RCAP2H and RCAP2L taken as a 16-bit unsigned
integer.
Timer 2 as a baud rate generator is shown in Figure 13-6. This figure is valid only if RCLK or
TCLK = 1 in T2CON. Note that a rollover in TH2 does not set TF2 and will not generate an interrupt. Note too, that if EXEN2 is set, a 1-to-0 transition in T2EX will set EXF2 but will not cause a
reload from (RCAP2H, RCAP2L) to (TH2, TL2). Thus when Timer 2 is in use as a baud rate generator, T2EX can be used as an extra external interrupt. Also note that the Baud Rate and
Frequency Generator modes may be used simultaneously.
97
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 13-6. Timer 2 in Baud Rate Generator Mode
TIMER 1 OVERFLOW
÷2
"0"
CLKSYS
"1"
SMOD1
C/T2 = 0
"1"
TL2
"0"
TH2
RCLK
÷16
TR2
Rx
CLOCK
C/T2 = 1
"1"
"0"
T2 PIN
RCAP2L
TRANSITION
DETECTOR
÷ 16
T2EX PIN
13.5
TCLK
RCAP2H
EXEN2
Tx
CLOCK
TIMER 2
INTERRUPT
EXF2
Frequency Generator (Programmable Clock Out)
Timer 2 can generate a 50% duty cycle clock on T2 (P1.0). This pin, besides being a regular I/O
pin, has two alternate functions. It can be programmed to input the external clock for
Timer/Counter 2 or to toggle its output at every timer overflow. To configure the Timer/Counter 2
as a clock generator, bit C/T2 (T2CON.1) must be cleared and bit T2OE (T2MOD.1) must be
set. Bit TR2 (T2CON.2) starts and stops the timer. The clock-out frequency depends on the system frequency and the reload value of Timer 2 capture registers (RCAP2H, RCAP2L), as shown
in the following equation.
f SYS
Clock Out Frequency = -----------------------------------------------------------------------------------------2   65536 –  RCAP2H,RCAP2L  
In the frequency generator mode, Timer 2 roll-overs will not generate an interrupt. This behavior
is similar to when Timer 2 is used as a baud-rate generator. It is possible to use Timer 2 as a
baud-rate generator and a clock generator simultaneously. Note, however, that the baud-rate
and clock-out frequencies cannot be determined independently from one another since they
both use RCAP2H and RCAP2L.
Figure 13-7. Timer 2 in Clock-out Mode
CLKSYS
TL2
TH2
RCAP2L
RCAP2H
TR2
C/T2
T2 PIN
÷2
T2EX PIN
EXF2
TRANSITION
DETECTOR
98
T2OE
TIMER 2
INTERRUPT
EXEN2
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
14. Programmable Counter Array (PCA)
The PCA provides more timing capabilities with less CPU intervention than the standard
timer/counters. Its advantages include reduced software overhead and improved accuracy. The
PCA consists of a dedicated timer/counter which serves as the time base for an array of five
compare/capture modules. Its clock input can be programmed to count any one of the following
signals:
• Peripheral clock frequency (FPERIPH) (TPS+1)
• Peripheral clock frequency (FPERIPH)  2
• Timer 0 overflow
• External input on ECI (P1.2)
Each compare/capture module can be programmed in any one of the following modes:
• Rising and/or falling edge capture
• Software timer
• High-speed output
• Pulse width modulator
Module 4 can also be programmed as a watchdog timer (see “PCA Watchdog Timer” on page
108).
When the compare/capture modules are programmed in the capture mode, software timer, or
high speed output mode, an interrupt can be generated when the module executes its function.
All five modules plus the PCA timer overflow share one interrupt vector.
The PCA timer/counter and compare/capture modules share Port 1 for external I/O. These pins
are listed below. If one or several bits in the port are not used for the PCA, they can still be used
for standard I/O.
Table 14-1.
14.1
PCA I/O Pins
PCA Component
External I/O Pin
16-bit Counter
P1.2/ECI
16-bit Module 0
P1.3/CEX0
16-bit Module 1
P1.4/CEX1
16-bit Module 2
P1.5/CEX2
16-bit Module 3
P1.6/CEX3
PCA Timer/Counter
The PCA timer is a common time base for all five modules (see Figure 14-1). The timer count
source is determined from the CPS1 and CPS0 bits in the CMOD register (Table 14-2) and can
be programmed to run at:
• 1/6 the peripheral clock frequency (FPERIPH)
• 1/2 the peripheral clock frequency (FPERIPH)
• The Timer 0 overflow
• The input on the ECI pin (P1.2)
99
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
The CMOD register includes three additional bits associated with the PCA (See Figure 14-1 and
Table 14-2).
• The CIDL bit which allows the PCA to stop during idle mode.
• The WDTE bit which enables or disables the watchdog function on module 4. (See Figure 144 and Section 14.7)
• The ECF bit which when set causes an interrupt and the PCA overflow flag CF (in the CCON
SFR) to be set when the PCA timer overflows.
Figure 14-1. PCA Timer/Counter
ECF
fPERIPH (TPS+1)
fPERIPH 2
Timer 0 Overflow
(P1.2) ECI
0
1
2
3
CL
Overflow
Interrupt
CF
To PCA
Modules
CPS1-0
Idle
CIDL
Table 14-2.
CH
CR
CCAPnL
CCAPnH
CMOD – PCA Counter Mode Register
CMOD Address = 0D9H
Reset Value = 00xx x000B
Not Bit Addressable
Bit
CIDL
WDTE
–
–
–
CPS1
CPS0
ECF
7
6
5
4
3
2
1
0
Symbol
Function
CIDL
Counter Idle Control
Clear to allow the PCA Counter to function during Idle Mode. Set to halt the PCA Counter during Idle.
WDTE
Watchdog Timer Enable
Clear to disable the watchdog timer function on PCA Module 4. Set to enable the watchdog function of PCA Module 4.
PCA Count Pulse Select
CPS1-0
ECF
CPS1
CPS0
PCA Clock Input
0
0
fPERIPH/(TPS+1) *Note: In Fast Mode TPS is only active when PCAX2 = 1 in CKCON0.
0
1
fPERIPH/2
1
0
Timer 0 Overflow
1
1
ECI Input (P1.2)
PCA Enable Counter Overflow Interrupt
Clear to prevent the CF bit in CCON from generating an interrupt. Set to enable CF in CCON as an interrupt source.
The CCON register contains the run control bit for the PCA and the flags for the PCA timer (CF)
and each module (Refer to Table 14-3).
• Bit CR (CCON.6) must be set by software to run the PCA. The PCA is shut off by clearing this
bit.
100
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
• Bit CF: The CF bit (CCON.7) is set when the PCA counter overflows and an interrupt will be
generated if the ECF bit in the CMOD register is set. The CF bit can only be cleared by
software.
• Bits 0 through 4 are the flags for the modules (bit 0 for module 0, bit 1 for module 1, etc.) and
are set by hardware when either a match or a capture occurs. These flags also can only be
cleared by software. The PCA interrupt system is shown in Figure 14-2.
Table 14-3.
CCON – PCA Counter Control Register
CCON Address = 0D8H
Reset Value = 00x0 0000B
Bit Addressable
Bit
CF
CR
–
CCF4
CCF3
CCF2
CCF1
CCF0
7
6
5
4
3
2
1
0
Symbol
Function
CF
PCA Counter Overflow Flag
Set by hardware when the PCA counter overflows from FFFFH to 0000H. CF generates an interrupt if the ECF bit in
CMOD and EC bit in IEN0 are both set. Must be cleared by software.
CR
PCA Counter Run Control
Clear to disable the PCA Counter from operating. Set to enable the PCA Counter to count at the CPS rate in CMOD.
CCF4
PCA Module 4 Interrupt Flag
Set by hardware when a compare of match occurs in Module 4. CCF4 generates an interrupt if the ECCF4 bit in CCAPM4
and EC bit in IEN0 are both set. Must be cleared by software.
CCF3
PCA Module 3 Interrupt Flag
Set by hardware when a compare of match occurs in Module 2. CCF3 generates an interrupt if the ECCF3 bit in CCAPM3
and EC bit in IEN0 are both set. Must be cleared by software.
CCF2
PCA Module 2 Interrupt Flag
Set by hardware when a compare of match occurs in Module 2. CCF2 generates an interrupt if the ECCF2 bit in CCAPM2
and EC bit in IEN0 are both set. Must be cleared by software.
CCF1
PCA Module 1 Interrupt Flag
Set by hardware when a compare of match occurs in Module 1. CCF1 generates an interrupt if the ECCF1 bit in CCAPM1
and EC bit in IEN0 are both set. Must be cleared by software.
CCF0
PCA Module 0 Interrupt Flag
Set by hardware when a compare of match occurs in Module 0. CCF0 generates an interrupt if the ECCF0 bit in CCAPM0
and EC bit in IEN0 are both set. Must be cleared by software.
Table 14-4.
CH – PCA Counter Register High
CH Address = 0F9H
Reset Value = 0000 0000B
Not Bit Addressable
Bit
C15
C14
C13
C12
C11
C10
C9
C8
7
6
5
4
3
2
1
0
Symbol
Function
C15-8
Module n Compare/Capture Register High
Holds the higher order bits of the 16-bit PCA Timer/Counter.
101
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 14-5.
CL – PCA Counter Register Low
CL Address = 0E9H
Reset Value = 0000 0000B
Not Bit Addressable
Bit
C7
C6
C5
C4
C3
C2
C1
C0
7
6
5
4
3
2
1
0
Symbol
Function
C7-0
Module n Compare/Capture Register Low
Holds the lower order bits of the 16-bit PCA Timer/Counter.
Figure 14-2. PCA Interrupt System
CMOD.0
CCON
Timer/Counter
7
ECF
CF
ECCF4
Module 4
4
CCF4
ECCF3
Module 3
3
IEN0.6
IEN0.7
EC
EA
CCF3
PCA Interrupt
to priority
decoder
ECCF2
Module 2
2
CCF2
ECCF1
Module 1
1
CCF1
ECCF0
Module 0
0
CCF0
CCAPMn.0
14.2
PCA Modules
Each one of the five compare/capture modules has six possible functions. It can perform:
• 16-bit Capture, positive-edge triggered
• 16-bit Capture, negative-edge triggered
• 16-bit Capture, both positive and negative-edge triggered
• 16-bit Software Timer
• 16-bit High Speed Output
• 8-bit Pulse Width Modulator
In addition, Module 4 can be used as a Watchdog Timer.
Each module in the PCA has a special function register associated with it. These registers are:
CCAPM0 for Module 0, CCAPM1 for Module 1, etc. (See Table 14-6). The registers contain the
bits that control the mode that each module will operate in.
• The ECCF bit (CCAPMn.0 where n = 0, 1, 2, 3, or 4 depending on the module) enables the
CCF flag in the CCON SFR to generate an interrupt when a match or compare occurs in the
associated module.
• PWM (CCAPMn.1) enables the pulse width modulation mode.
102
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
• The TOG bit (CCAPMn.2) when set causes the CEX output associated with the module to
toggle when there is a match between the PCA counter and the modules capture/compare
register.
• The match bit MAT (CCAPMn.3) when set will cause the CCFn bit in the CCON register to be
set when there is a match between the PCA counter and the modules capture/compare
register.
• The next two bits CAPN (CCAPMn.4) and CAPP (CCAPMn.5) determine the edge that a
capture input will be active on. The CAPN bit enables the negative edge, and the CAPP bit
enables the positive edge. If both bits are set both edges will be enabled and a capture will
occur for either transition.
• The last bit in the register ECOM (CCAPMn.6) when set enables the comparator function.
Table 14-6 shows the CCAPMn settings for the various PCA functions.
Table 14-6.
CCAPMn – PCA Module n Compare/Capture Control Register (n = 0–4)
CCAPM0 Address = 0DAH
Reset Value = x000 0000B
CCAPM1 Address = 0DBH
CCAPM2 Address = 0DCH
CCAPM3 Address = 0DDH
CCAPM4 Address = 0DEH
Not Bit Addressable
Bit
–
ECOMn
CAPPn
CAPNn
MATn
TOGn
PWMn
ECCFn
7
6
5
4
3
2
1
0
Symbol
Function
ECOMn
Enable Comparator
Clear to disable the comparator function of Module n. Set to enable the comparator function of Module n
CAPPn
Capture Positive
Clear to disable positive edge capture for Module n. Set to enable positive edge capture for Module n.
CAPNn
Capture Negative
Clear to disable negative edge capture for Module n. Set to enable negative edge capture for Module n.
MATn
Match Enable
When MATn = 1 and ECOMn = 1 a match between the PCA counter and Module n’s compare/capture register will set the
CCFn bit in CCON. Clear MATn to disable setting of CCFn by compare events.
TOGn
Toggle Output
When TOGn = 1 and ECOMn = 1 a match between the PCA counter and Module n’s compare/capture register will toggle
the CEXn pin. Clear TOGn to disable toggling of CEXn by compare events.
PWMn
Pulse Width Modulation Enable
Set to configure Module n in PWM mode and use CEXn as a PWM output. Clear to disable PWM mode for Module n.
ECCFn
Enable CCFn Interrupt
Clear to disable the CCFn bit in CCON as an interrupt source. Set to enable the CCFn bit in CCON to generate interrupts.
103
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Note:
PCA Module Modes (CCAPMn Registers
ECOMn
CAPPn
CAPNn
MATn
TOGn
PWMn
ECCFn
Module Function
0
0
0
0
0
0
0
No Operation
X
1
0
0
0
0
X
16-bit capture by a positive-edge trigger on CEXn
X
0
1
0
0
0
X
16-bit capture by a negative trigger on CEXn
X
1
1
0
0
0
X
16-bit capture by a transition on CEXn
1
0
0
1
0
0
X
16-bit Software Timer/Compare mode.
1
0
0
1
1
0
X
16-bit High Speed Output
1
0
0
0
0
1
0
8-bit PWM
1
0
0
1
X
0
X
Watchdog Timer (module 4 only)
There are two additional registers associated with each of the PCA modules. They are CCAPnH and CCAPnL and these
are the registers that store the 16-bit count when a capture occurs or a compare should occur. When a module is used in
the PWM mode these registers are used to control the duty cycle of the output (See Table 14-7 & Table 14-8).
Table 14-7.
CCAPnH – PCA Module n Compare/Capture Register High (n = 0–4)
CCAP0H Address = 0FAH
Reset Value = 0000 0000B
CCAP1H Address = 0FBH
CCAP2H Address = 0FCH
CCAP3H Address = 0FDH
CCAP4H Address = 0FEH
Not Bit Addressable
CCAPn.15
CCAPn.14
CCAPn.13
CCAPn.12
CCAPn.11
CCAPn.10
CCAPn.9
CCAPn.8
7
6
5
4
3
2
1
0
Bit
Symbol
Function
CCAPn15-8
Module n Compare/Capture Register High
Holds the higher order bits of the 16-bit Compare/Capture value for Module n.
Table 14-8.
CCAPnL – PCA Module n Compare/Capture Register Low (n = 0–4)
CCAP0L Address = 0EAH
Reset Value = 0000 0000B
CCAP1L Address = 0EBH
CCAP2L Address = 0ECH
CCAP3L Address = 0EDH
CCAP4L Address = 0EEH
Not Bit Addressable
CCAPn.7
CCAPn.6
CCAPn.5
CCAPn.4
CCAPn.3
CCAPn.2
CCAPn.1
CCAPn.0
7
6
5
4
3
2
1
0
Bit
Symbol
Function
CCAPn7-0
Module n Compare/Capture Register Low
Holds the lower order bits of the 16-bit Compare/Capture value for Module n.
104
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
14.3
PCA Capture Mode
To use one of the PCA modules in the capture mode either one or both of the CCAPM bits
CAPN and CAPP for that module must be set. The external CEX input for the module (on port 1)
is sampled for a transition. When a valid transition occurs the PCA hardware loads the value of
the PCA counter registers (CH and CL) into the module's capture registers (CCAPnL and
CCAPnH). If the CCFn bit for the module in the CCON SFR and the ECCFn bit in the CCAPMn
SFR are set then an interrupt will be generated (Refer to Figure 14-3).
Figure 14-3. PCA Capture Mode
CL
CH
CCAPMn.0
ECCFn
CAPPn
CEXn
Interrupt
CCAPnL CCAPnH
CCAPMn.5
CCFn
CAPNn
Module n
CCAPMn.4
14.4
16-bit Software Timer/ Compare Mode
The PCA modules can be used as software timers by setting both the ECOM and MAT bits in
the modules CCAPMn register. The PCA timer will be compared to the module's capture registers and when a match occurs an interrupt will occur if the CCFn (CCON SFR) and the ECCFn
(CCAPMn SFR) bits for the module are both set (See Figure 14-4).
Figure 14-4. PCA Compare Mode and PCA Watchdog Timer
1
0
Write to
CCAPnH
CL
Write to
CCAPnL
CH
ECOMn
=
CCFn
MATn
CCAPMn.3
Interrupt
ECCFn
CCAPMn.0
Reset
CCAPnL CCAPnH
WDTE
CMOD.6 (Module 4 only)
Module n
Before enabling ECOM bit, CCAPnL and CCAPnH should be set with a non zero value, otherwise an unwanted match could happen. Writing to CCAPnH will set the ECOM bit. Once ECOM
is set, writing CCAPnL will clear ECOM so that an unwanted match doesn’t occur while modifying the compare value. Writing to CCAPnH will set ECOM. For this reason, user software should
write CCAPnL first, and then CCAPnH. Of course, the ECOM bit can still be controlled by
accessing to CCAPMn register.
105
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
14.5
High Speed Output Mode
In this mode the CEX output (on port 1) associated with the PCA module will toggle each time a
match occurs between the PCA counter and the modules capture registers as shown in Figure
14-6. To activate this mode the TOG, MAT, and ECOM bits in the module's CCAPMn SFR must
be set (See Figure 14-5).
A prior write must be done to CCAPnL and CCAPnH before writing the ECOMn bit.
Figure 14-5. PCA High Speed Output Mode
1
0
Write to
CCAPnH
CL
Write to
CCAPnL
CH
ECOMn
=
CCFn
MATn
CCAPMn.3
Interrupt
ECCFn
CCAPMn.0
CEXn
CCAPnL CCAPnH
TOGn
CCAPMn.2
Module n
Before enabling ECOM bit, CCAPnL and CCAPnH should be set with a non zero value, otherwise an unwanted match could happen. Once ECOM is set, writing CCAPnL will clear ECOM so
that an unwanted match doesn’t occur while modifying the compare value. Writing to CCAPnH
will set ECOM. For this reason, user software should write CCAPnL first, and then CCAPnH. Of
course, the ECOM bit can still be controlled by accessing to CCAPMn register.
An example of a High Speed Output waveform is shown in Figure 14-6. The frequency of the
output can be controlled by reloading the PCA Timer in software and/or changing the compare
values multiple times per timeout period.
Figure 14-6. High Speed Output Waveform
TOGn = 1, ECOMn = 1
{CH,CL} = FFFFH
{CCAPnH,CCAPnL}
{CH,CL} = 0000H
CEXn
106
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
14.6
Pulse Width Modulator Mode
All of the PCA modules can be used as PWM outputs. Figure 14-7 shows the PWM function.
The frequency of the output depends on the source for the PCA timer. All of the modules will
have the same frequency of output because they all share the PCA timer. The duty cycle of each
module is independently variable using the modules capture register CCAPnL. When the value
of the PCA CL SFR is less than the value in the modules CCAPnL SFR the output will be low,
when it is equal to or greater than the output will be high. When CL overflows from FFH to 00H,
CCAPnL is reloaded with the value in CCAPnH. This allows updating the PWM without glitches.
The PWM and ECOM bits in the module's CCAPMn register must be set to enable the PWM
mode. The following equations show the resulting frequency and duty cycles of the generated
output:
f SYS
1
f out = ------------  --------------------256 TPS + 1
– CCAPnLDuty Cycle % = 100  256
-------------------------------------256
CPS = 00B:
Figure 14-7. PCA PWM Mode
CL
ECOMn
+
>
CEXn
–
CCAPnL
ECOMn
PWMn
CCAPMn.6
CCAPMn.1
CCAPnH
Module n
An example PCA PWM waveform is shown in Figure 14-8.
Figure 14-8. PCA PWM Waveform
PWMn = 1, ECOMn = 1
CL = FFH
CCAPnH
CL = 00H
CEXn
107
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
14.7
PCA Watchdog Timer
An on-board watchdog timer is available with the PCA to improve the reliability of the system
without increasing chip count. Watchdog timers are useful for systems that are susceptible to
noise, power glitches, or electrostatic discharge. Module 4 is the only PCA module that can be
programmed as a watchdog. However, this module can still be used for other modes if the
watchdog is not needed. Figure 14-4 shows a diagram of how the watchdog works. The user
pre-loads a 16-bit value in the compare registers. Just like the other compare modes, this 16-bit
value is compared to the PCA timer value. If a match is allowed to occur, an internal reset will be
generated. This reset will not cause the RST pin to be driven active.
In order to hold off the reset, the user has three options:
1. Periodically change the compare value so it will never match the PCA timer.
2. Periodically change the PCA timer value so it will never match the compare values.
3. Disable the watchdog by clearing the WDTE bit before a match occurs and then reenable it.
The first two options are more reliable because the watchdog timer is never disabled as in option
#3. If the program counter ever goes astray, a match will eventually occur and cause an internal
reset. The second option is also not recommended if other PCA modules are being used.
Remember, the PCA timer is the time base for all modules; changing the time base for other
modules would not be a good idea. Thus, in most applications the first solution is the best option.
This watchdog timer won’t generate a reset out on the reset pin. Only the Hardware Watchdog
can generate a board-level reset.
15. Hardware Watchdog Timer
The programmable Hardware Watchdog Timer (WDT) protects the system from incorrect execution by triggering a system reset when it times out after the software has failed to feed the timer
prior to the timer overflow. Each WDT clock cycle depends on the Timer Prescaler (see Section
6.9 on page 52). By Default the WDT counts every 6 CPU clock cycles since TPS = 5. The prescaler bits, WTO0, WTO1 and WTO2 in SFR WDTPRG are used to set the period of the
Watchdog Timer from 16K to 2048K WDT clock cycles. The WDT is disabled by Reset and during Power-down mode. When the WDT times out without being serviced, a RST pulse last 96
system clocks (48 system clocks in X2 Mode) is generated to reset the CPU. This reset is also
driven out on the RST pin (see Section 7.4 on page 58) if the DISRTO bit in WDTPRG is not set.
See Table 15-1 for the available WDT period selections
 WTO + 14 
2
Time-out Period = -----------------------------   TPS + 1 
f SYS
The Watchdog Timer consists of a 14-bit timer with 7-bit programmable prescaler. Writing the
sequence 1EH/E1H to the WDTRST register enables the timer. When the WDT is enabled, the
WDTEN bit in WDTPRG will be set to “1”. To prevent the WDT from generating a reset when if
overflows, the watchdog feed sequence must be written to WDTRST before the end of the timeout period. To feed the watchdog, two write instructions must be sequentially executed successfully. Between the two write instructions, SFR reads are allowed, but writes are not allowed. The
instructions should move 1EH to the WDTRST register and then 1EH to the WDTRST register.
An incorrect feed or enable sequence will cause an immediate watchdog reset.
108
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
The program sequence to feed or enable the watchdog timer is as follows:
MOV WDTRST, #01Eh
MOV WDTRST, #0E1h
Table 15-1.
Watchdog Timer Time-out Period Selection
WDT Prescaler Bits
WTO2
WTO1
WTO0
Period()
(Clock Cycles)
0
0
0
16K x (TPS+1)
0
0
1
32K x (TPS+1)
0
1
0
64K x (TPS+1)
0
1
1
128K x (TPS+1)
1
0
0
256K x (TPS+1)
1
0
1
512K x (TPS+1)
1
1
0
1024K x (TPS+1)
1
1
1
2048K x (TPS+1)
The WDT time-out period is dependent on the system clock frequency.
15.1
Software Reset
A Software Reset of the AT89LP51RD2/ED2/ID2 is accomplished by writing the software reset
sequence 5AH/A5H to the WDTRST SFR. The WDT does not need to be enabled to generate
the software reset. A normal software reset will set the SWRST flag in WDTCON. However, if at
any time an incorrect sequence is written to WDTRST (i.e. anything other than 1EH/E1H or
5AH/A5H), a software reset will immediately be generated and both the SWRST and WDTOVF
flags will be set. In this manner an intentional software reset may be distinguished from a software error-generated reset. The program sequence to generate a software reset is as follows:
MOV WDTRST, #05Ah
MOV WDTRST, #0A5h
A software reset has the same duration as the normal watchdog reset and will also generate a
reset pulse on the RST pin unless DISRTO is set.
109
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
15.2
WDT Registers
)
Table 15-2.
WDTPRG – Watchdog Control Register
WDTPRG Address = A7H
Reset Value = xx00 0000B
Not Bit Addressable
WDTOVF
SWRST
WDTEN
WDIDLE
DISRTO
WTO2
WTO1
WTO0
7
6
5
4
3
2
1
0
Bit
Symbol
Function
WDTOVF
Watchdog Overflow Flag
Set by hardware when a WDT rest is generated by the WDT timer overflow. Also set when an incorrect sequence is
written to WDTRST. Must be cleared by software.
SWRST
Software Reset Flag
Set by hardware when a software reset is generated by writing the sequence 5AH/A5H to WDTRST. Also set when an
incorrect sequence is written to WDTRST. Must be cleared by software.
WDTEN
Watchdog Enable Flag
This bit is READ-ONLY and reflects the status of the WDT (whether it is running or not). The WDT is disabled after any
reset and must be re-enabled by writing 1EH/E1H to WDTRST
WDIDLE
WDT Disable During Idle
When WDIDLE = 0 the WDT continues to count in Idle mode. When WDIDLE = 1 the WDT halts counting in Idle mode.
DISRTO
Disable Reset Output
When DISTRO = 0 the reset pin is driven to the same level as POL when the WDT resets. When DISRTO = 1 the reset
pin is input only.
WTO2
WTO1
WTO0
Watchdog Tiemout
Prescaler bits for the watchdog timer (WDT). When all three bits are cleared to 0, the watchdog timer has a nominal
period of 16K clock cycles. When all three bits are set to 1, the nominal period is 2048K clock cycles.
Table 15-3.
WDTRST – Watchdog Reset Register
WDTCON Address = A6H
(Write-Only)
Not Bit Addressable
Bit
–
–
–
–
–
–
–
–
7
6
5
4
3
2
1
0
The WDT is enabled by writing the sequence 1EH/E1H to the WDTRST SFR. The current status may be checked by reading
the WDTEN bit in WDTCON. To prevent the WDT from resetting the device, the same sequence 1EH/E1H must be written to
WDTRST before the time-out interval expires. A software reset is generated by writing the sequence 5AH/A5H to WDTRST.
110
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
16. Serial Interface (UART)
The serial interface on the AT89LP51RD2/ED2/ID2 implements a Universal Asynchronous
Receiver/Transmitter (UART). The UART has the following features:
•
•
•
•
•
•
•
Full-duplex Operation
8 or 9 Data Bits
Framing Error Detection
Multiprocessor Communication Mode with Automatic Address Recognition
Baud Rate Generator Using Timer 1, Timer 2 or dedicated Internal Baud Rate Generator
Interrupt on Receive Buffer Full or Transmission Complete
Synchronous SPI or TWI Master Emulation
The serial interface is full-duplex, which means it can transmit and receive simultaneously. It is
also receive-buffered, which means it can begin receiving a second byte before a previously
received byte has been read from the receive register. (However, if the first byte still has not
been read when reception of the second byte is complete, one of the bytes will be lost.) The
serial port receive and transmit registers are both accessed at the Special Function Register
SBUF. Writing to SBUF loads the transmit register, and reading SBUF accesses a physically
separate receive register. The serial port can operate in the following four modes.
• Mode 0: Serial data enters and exits through RXD. TXD outputs the shift clock. Eight data
bits are transmitted/received, with the LSB first. The baud rate is programmable to 1/6 or 1/3
the system frequency in Compatibility mode, 1/4 or 1/2 the system frequency in Fast mode,
or variable based on Time 1.
• Mode 1: 10 bits are transmitted (through TXD) or received (through RXD): a start bit (0),
8 data bits (LSB first), and a stop bit (1). On receive, the stop bit goes into RB8 in the Special
Function Register SCON. The baud rate is variable based on Timer 1 or Timer 2.
• Mode 2: 11 bits are transmitted (through TXD) or received (through RXD): a start bit (0),
8 data bits (LSB first), a programmable 9th data bit, and a stop bit (1). On transmit, the 9th
data bit (TB8 in SCON) can be assigned the value of “0” or “1”. For example, the parity bit
(P, in the PSW) can be moved into TB8. On receive, the 9th data bit goes into RB8 in the
Special Function Register SCON, while the stop bit is ignored. The baud rate is
programmable to either 1/16 or 1/32 the system frequency.
• Mode 3: 11 bits are transmitted (through TXD) or received (through RXD): a start bit (0),
8 data bits (LSB first), a programmable 9th data bit, and a stop bit (1). In fact, Mode 3 is the
same as Mode 2 in all respects except the baud rate, which is variable based on Timer 1 or
Timer 2 in Mode 3.
In all four modes, transmission is initiated by any instruction that uses SBUF as a destination
register. Reception is initiated in Mode 0 by the condition RI = 0 and REN = 1. Reception is initiated in the other modes by the incoming start bit if REN = 1.
111
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 16-1.
SCON – Serial Port Control Register
SCON Address = 98H
Reset Value = 0000 0000B
Bit Addressable
Bit
SM0/FE
SM1
SM2
REN
TB8
RB8
T1
RI
7
6
5
4
3
2
1
0
(SMOD0 = 0/1)(1)
Symbol
Function
FE
Framing Error Bit
This bit is set by the receiver when an invalid stop bit is detected. The FE bit is not cleared by valid frames and must be
cleared by software. The SMOD0 bit must be set to enable access to the FE bit. FE will be set regardless of the state of
SMOD0.
SM0
Serial Port Mode Bit 0
Refer to SM1 for serial port mode selection. SMOD0 must = 0 to access bit SM0.
Serial Port Mode Bit 1
SM1
SM0
SM1
Mode
Description
Baud Rate (Compat.)(2)
Baud Rate (Fast)(2)
0
0
0
shift register
fSYS/3 or fSYS/6 or Timer 1
fSYS/2 or fSYS/4 or Timer 1
0
1
1
8-bit UART
variable (Timer 1 or Timer 2)
variable (Timer 1 or Timer 2)
1
0
2
9-bit UART
fSYS/32 or fSYS/16
fSYS/32 or fSYS/16
1
1
3
9-bit UART
variable (Timer 1 or Timer 2)
variable (Timer 1 or Timer 2)
SM2
Multiprocessor Communications Enable
Enables the Automatic Address Recognition feature in Modes 2 or 3. If SM2 = 1 then Rl will not be set unless the received
9th data bit (RB8) is 1, indicating an address, and the received byte is a Given or Broadcast Address. In Mode 1, if SM2 =
1 then Rl will not be activated unless a valid stop bit was received, and the received byte is a Given or Broadcast Address.
In Mode 0, SM2 determines the idle state of the shift clock such that the clock is the inverse of SM2, i.e. when SM2 = 0
the clock idles high and when SM2 = 1 the clock idles low.
REN
Serial Reception Enable
Set by software to enable reception. Clear by software to disable reception.
TB8
Transmitter Bit 8
The 9th data bit that will be transmitted in Modes 2 and 3. Set or clear by software as desired. In Mode 0, setting TB8
enables Timer 1 as the shift clock generator.
RB8
Receiver Bit 8
In Modes 2 and 3, the 9th data bit that was received. In Mode 1, if SM2 = 0, RB8 is the stop bit that was received. In Mode
0, RB8 is not used.
TI
Transmit Interrupt Flag
Set by hardware at the end of the 8th bit time in Mode 0, or at the beginning of the stop bit in the other modes, in any
serial transmission. Must be cleared by software.
RI
Receive Interrupt Flag
Set by hardware at the end of the 8th bit time in Mode 0, or halfway through the stop bit time in the other modes, in any
serial reception (except see SM2). Must be cleared by software.
Notes:
112
1. SMOD0 is located at PCON.6.
2. fSYS = system frequency. The baud rate depends on SMOD1 (PCON.7).
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
16.1
Multiprocessor Communications
Modes 2 and 3 have a special provision for multiprocessor communications. In these modes,
9 data bits are received, followed by a stop bit. The 9th bit goes into RB8. Then comes a stop bit.
The port can be programmed such that when the stop bit is received, the serial port interrupt is
activated only if RB8 = 1. This feature is enabled by setting bit SM2 in SCON.
The following example shows how to use the serial interrupt for multiprocessor communications.
When the master processor must transmit a block of data to one of several slaves, it first sends
out an address byte that identifies the target slave. An address byte differs from a data byte in
that the 9th bit is “1” in an address byte and “0” in a data byte. With SM2 = 1, no slave is
interrupted by a data byte. An address byte, however, interrupts all slaves. Each slave can
examine the received byte and see if it is being addressed. The addressed slave clears its SM2
bit and prepares to receive the data bytes that follows. The slaves that are not addressed set
their SM2 bits and ignore the data bytes. See “Automatic Address Recognition” on page 118.
The SM2 bit can be used to check the validity of the stop bit in Mode 1. In a Mode 1 reception, if
SM2 = 1, the receive interrupt is not activated unless a valid stop bit is received.
16.2
Baud Rates
The baud rate in Mode 0 depends on the value of the SMOD1 bit in Special Function Register
PCON.7. If SMOD1 = 0 (the value on reset) and TB8 = 0, the baud rate is 1/4 of the system frequency in Fast mode. If SMOD1 = 1 and TB8 = 0, the baud rate is 1/2 of the system frequency,
as shown in the following equation:
SMOD1
Mode 0 Baud Rate
= 2
--------------------  System Frequency
4
TB8 = 0
In Compatibility mode the baud rate is 1/6 of the system frequency, scaling to 1/3 when
SMOD1 = 1.
SMOD1
Mode 0 Baud Rate
2
= --------------------  System Frequency
6
TB8 = 0
Mode 0 can also be generated from either Timer 1 or the Internal Baud Rate Generator by setting TB8 in SCON or SRC in BDRCON respectively.
The baud rate in Mode 2 also depends on the value of the SMOD1 bit. If SMOD1 = 0, the baud
rate is 1/32 of the system frequency. If SMOD1 = 1, the baud rate is 1/16 of the system frequency, as shown in the following equation:
SMOD1
2
Mode 2 Baud Rate = --------------------  System Frequency
32
The baud rate in Modes 1 and 3 is generated from one of Timer 1, Timer 2 or the Internal Baud
Rate Generator as detailed in Table 16-2.
113
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 16-2.
16.2.1
UART Baud Rate Selection Table for Modes 1 and 3
TCLK
(T2CON.4)
RCLK
(T2CON.5)
TBCK
(BDRCON.3)
RBCK
(BDRCON.2)
Clock Source
UART Tx
Clock Source
UART Rx
0
0
0
0
Timer 1
Timer 1
1
0
0
0
Timer 2
Timer 1
0
1
0
0
Timer 1
Timer 2
1
1
0
0
Timer 2
Timer 2
X
0
1
0
BRG
Timer 1
X
1
1
0
BRG
Timer 2
0
X
0
1
Timer 1
BRG
1
X
0
1
Timer 2
BRG
X
X
1
1
BRG
BRG
Using Timer 1 to Generate Baud Rates
Setting TB8 = 1 in Mode 0 enables Timer 1 as the baud rate generator. When Timer 1 is the
baud rate generator for Mode 0, the baud rates are determined by the Timer 1 overflow rate and
the value of SMOD1 according to the following equation:
SMOD1
Mode 0 Baud Rate
= 2
--------------------  (Timer 1 Overflow Rate)
4
TB8 = 1
The Timer 1 overflow rate normally determines the baud rates in Modes 1 and 3. When Timer 1
is the baud rate generator, the baud rates are determined by the Timer 1 overflow rate and the
value of SMOD1 according to the following equation:
SMOD1
Modes 1, 3
2
= --------------------  (Timer 1 Overflow Rate)
32
Baud Rate
The Timer 1 interrupt should be disabled in this application. The Timer itself can be configured
for either timer or counter operation in any of its 3 running modes. In the most typical applications, it is configured for timer operation in auto-reload mode (high nibble of TMOD = 0010B). In
this case, the baud rate is given by the following formula:
SMOD1
Modes 1, 3
Frequency-  -------------------1 = 2
--------------------  System
------------------------------------------------32

256
–

TH1


TPS
+1
Baud Rate
Table 16-3 lists commonly used baud rates and how they can be obtained from Timer 1.
114
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 16-3.
Commonly Used Baud Rates Generated by Timer 1
Timer 1
Baud Rate
fOSC (MHz)
X2
SMOD1
C/T
Mode
TPS
Reload Value
Mode 0 Max: 6 MHz
12
1
1
X
X
0
X
Mode 2 Max: 750K
12
1
1
X
X
0
X
Modes 1, 3 Max: 750K
12
1
1
0
2
0
F4H
19.2K
11.059
1
1
0
2
0
DCH
9.6K
11.059
1
0
0
2
0
DCH
4.8K
11.059
1
0
0
2
0
B8H
2.4K
11.059
1
0
0
2
0
70H
1.2K
11.059
1
0
0
1
0
FEE0H
137.5
11.986
1
0
0
1
0
F55CH
110
6
1
1
0
1
0
F2AFH
110
12
1
0
0
1
0
F2AFH
19.2K
11.059
0
1
0
2
5
FDH
9.6K
11.059
0
0
0
2
5
FDH
4.8K
11.059
0
0
0
2
5
FAH
2.4K
11.059
0
0
0
2
5
F4H
1.2K
11.059
0
0
0
2
5
E8H
137.5
11.986
0
0
0
2
5
1DH
110
6
0
0
0
2
5
72H
110
12
0
0
0
1
5
FEEBH
16.2.2
Using Timer 2 to Generate Baud Rates
Timer 2 is selected as the baud rate generator by setting TCLK and/or RCLK in T2CON. Under
these conditions, the baud rates for transmit and receive can be simultaneously different by
using Timer 1 for transmit and Timer 2 for receive, or vice versa. The baud rate generator mode
is similar to the auto-reload mode, in that a rollover causes the Timer 2 registers to be reloaded
with the 16-bit value in registers RCAP2H and RCAP2L, which are preset by software. In this
case, the baud rates in Modes 1 and 3 are determined by Timer 2’s overflow rate according to
the following equation:
Modes 1 and 3
1-  --------------------------------------------------------------------------------System Frequency
= ----16  65536 –  RCAP2H,RCAP2L  
Baud Rate
Table 16-4 lists commonly used baud rates and how they can be obtained from Timer 2. Note
that TPS and T2X2 do not apply to Timer 2 in baud rate mode.
115
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 16-4.
Commonly Used Baud Rates Generated by Timer 2
Timer 2
16.2.3
Baud Rate
fOSC (MHz)
X2
CP/RL2
C/T2
TCLK or RCLK
Reload Value
Max: 750K
12
1
0
0
1
FFFFH
19.2K
11.059
1
0
0
1
FFDCH
9.6K
11.059
1
0
0
1
FFB8H
4.8K
11.059
1
0
0
1
FF70H
2.4K
11.059
1
0
0
1
FEE0H
1.2K
11.059
1
0
0
1
FDC0H
137.5
11.986
1
0
0
1
EAB8H
110
6
1
0
0
1
F2AFH
110
12
1
0
0
1
E55EH
19.2K
11.059
0
0
0
1
FFEEH
9.6K
11.059
0
0
0
1
FFDCH
4.8K
11.059
0
0
0
1
FFB8H
2.4K
11.059
0
0
0
1
FF70H
1.2K
11.059
0
0
0
1
FEE0H
137.5
11.986
0
0
0
1
F55CH
110
12
0
0
0
1
F2AFH
Internal Baud Rate Generator (BRG)
The AT89LP51RD2/ED2/ID2 includes an Internal Baud Rate Generator (BRG) for UART modes
1 and 3 that can free up Timer 1 or Timer 2 for other uses. The BRG is an 8-bit counter with
reload as shown in Figure 16-1. On overflow, the BRG is loaded with the value of BRL. The BRG
is controlled by the BDRCON register (See Table 16-7). The BRG operates when BRR = 1. The
SPD bit determines the clock source: either the system clock divided-by-6 or the system clock
with no division. The BRG is not affected by the Timer Prescaler; however, it is affected by the
SMOD1 bit in PCON. The following equation shows the baud rate calculation using the BRG:
SMOD1
f SYS
2
1
Baud Rate = --------------------  -------------------------------  -----------------------32
256 –  BRL  6  1 – SPD 
The output of the Internal Baud Rate Generator can be independently selected for the transmit
and receive clocks using the TBCK and RBCK bits in BDRCON. These bits have priority over
the TCLK and TCLK bits in T2CON as shown in Table 16-2. Table 16-5 lists some common
baud rates generated by the BRG.
116
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 16-1. Internal Baud Rate Generator
BRL
Overflow
6
CLKSYS
0
6
BRG
0
1
UART
1
SPD
BRR
(BDRCON.1) (BDRCON.4)
SMOD1
(PCON.7)
Table 16-5.
Commonly Used Baud Rates Generated by BRG
fOSC = 16.384 MHz
Table 16-6.
fOSC = 24 MHz
Baud Rate
X2
SMOD1
SPD
BRL
Error (%)
BRL
Error (%)
115200
1
1
1
247
1.23
243
0.16
57600
1
1
1
238
1.23
230
0.16
38400
1
1
1
229
1.23
217
0.16
28800
1
1
1
220
1.23
204
0.16
19200
1
1
1
203
0.63
178
0.16
9600
1
1
1
149
0.31
100
0.16
4800
1
1
1
43
1.23
–
–
4800
0
0
0
247
1.23
243
0.16
2400
0
0
0
238
1.23
230
0.16
1200
0
0
0
220
1.23
202
3.55
600
0
0
0
185
0.16
152
0.16
BRL – Baud Rate Reload Register
BRL Address = 09AH
Reset Value = 0000 0000B
Not Bit Addressable
Bit
7
6
5
4
3
2
1
0
Symbol
Function
BRL7-0
Baud Rate Reload Value
Holds the 8-bit reload value of the Internal Baud Rate Generator. This value is loaded into the BRG when the BRG
overflows from FFH to 00H.
117
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 16-7.
BDRCON – Baud Rate Control Register
BDRCON Address = 9BH
Reset Value = xxx0 0000B
Not Bit Addressable
Bit
–
–
–
BRR
TBCK
RBCK
SPD
SRC
7
6
5
4
3
2
1
0
Symbol
Function
BRR
Baud Rate Run Control
Clear to stop the Internal Baud Rate Generator. Set to start the Internal Baud Rate Generator.
TBCK
Transmission Baud Rate Select
Clear to select Timer 1 or Timer 2 overflow as transmit clock for the serial port. Set to select the Internal Baud Rate
Generator as transmit clock for the serial port.
RBCK
Receive Baud Rate Select
Clear to select Timer 1 or Timer 2 overflow as receive clock for the serial port. Set to select the Internal Baud Rate
Generator as receive clock for the serial port.
SPD
BRG Speed Control
Clear to select the SLOW baud rate generator mode. Set to select the FAST baud rate generator mode.
SRC
Baud Rate Source for Mod e 0
Clear to select fixed or Timer 1 clock source for UART mode 0. Set to select BRG for UART mode 0.
16.3
Framing Error Detection
In addition to all of its usual modes, the UART can perform framing error detection by looking for
missing stop bits. When used for framing error detect, the UART looks for missing stop bits in
the communication. A missing bit will set the FE bit in the SCON register. The FE bit shares the
SCON.7 bit with SM0 and the function of SCON.7 is determined by PCON.6 (SMOD0). If
SMOD0 is set then SCON.7 functions as FE. SCON.7 functions as SM0 when SMOD0 is
cleared. When used as FE, SCON.7 can only be cleared by software. The FE bit will be set by a
framing error regardless of the state of SMOD0.
16.4
Automatic Address Recognition
Automatic Address Recognition is a feature which allows the UART to recognize certain
addresses in the serial bit stream by using hardware to make the comparisons. This feature
saves a great deal of software overhead by eliminating the need for the software to examine
every serial address which passes by the serial port. This feature is enabled by setting the SM2
bit in SCON for Modes 1, 2 or 3. In the 9-bit UART modes, Mode 2 and Mode 3, the Receive
Interrupt flag (RI) will be automatically set when the received byte contains either the “Given”
address or the “Broadcast” address. The 9-bit mode requires that the 9th information bit be a “1”
to indicate that the received information is an address and not data.
In Mode 1 (8-bit) the RI flag will be set if SM2 is enabled and the information received has a valid
stop bit following the 8th address bits and the information is either a Given or Broadcast
address. Using the Automatic Address Recognition feature allows a master to selectively communicate with one or more slaves by invoking the given slave address or addresses. All of the
slaves may be contacted by using the Broadcast address. Automatic Address Recognition is not
available during Mode 0.
118
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
16.4.1
Given Address
Two special Function Registers are used to define the slave’s address, SADDR (A9H), and the
address mask, SADEN (B9H). SADEN is used to define which bits in the SADDR are to be used
and which bits are “don’t care”. The SADEN mask can be logically ANDed with the SADDR to
create the “Given” address which the master will use for addressing each of the slaves. Use of
the Given address allows multiple slaves to be recognized while excluding others. The following
examples show the versatility of this scheme:
Slave 0
SADDR = 1100 0000
SADEN = 1111 1101
Given = 1100 00X0
Slave 1
SADDR = 1100 0000
SADEN = 1111 1110
Given = 1100 000X
In the previous example, SADDR is the same and the SADEN data is used to differentiate
between the two slaves. Slave 0 requires a “0” in bit 0 and it ignores bit 1. Slave 1 requires a “0”
in bit 1 and bit 0 is ignored. A unique address for slave 0 would be 1100 0010 since slave 1
requires a “0” in bit 1. A unique address for slave 1 would be 1100 0001 since a “1” in bit 0 will
exclude slave 0. Both slaves can be selected at the same time by an address which has bit 0 = 0
(for slave 0) and bit 1 = 0 (for slave 1). Thus, both could be addressed with 1100 0000.
In a more complex system, the following could be used to select slaves 1 and 2 while excluding
slave 0:
Slave 0
SADDR = 1100 0000
SADEN = 1111 1001
Given = 1100 0XX0
Slave 1
SADDR = 1110 0000
SADEN = 1111 1010
Given = 1110 0X0X
Slave 2
SADDR = 1110 0000
SADEN = 1111 1100
Given = 1110 00XX
In the above example, the differentiation among the 3 slaves is in the lower 3 address bits. Slave
0 requires that bit 0 = 0 and it can be uniquely addressed by 1110 0110. Slave 1 requires that
bit 1 = 0 and it can be uniquely addressed by 1110 and 0101. Slave 2 requires that bit 2 = 0 and
its unique address is 1110 0011. To select Slaves 0 and 1 and exclude Slave 2, use address
1110 0100, since it is necessary to make bit 2 = 1 to exclude slave 2.
Upon reset the SADDR and SADEN registers are loaded with “0”s. This produces a given
address of all “don’t cares” as well as a Broadcast address of all “don’t cares”. This effectively
disables the Automatic Addressing mode and allows the microcontroller to use standard 80C51type UART drivers which do not make use of this feature.
119
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
16.4.2
Broadcast Address
The Broadcast Address for each slave is created by taking the logic OR of SADDR and SADEN.
Zeros in this result are trended as don’t cares. In most cases, interpreting the don’t cares as
ones, the broadcast address will be FF hexadecimal.
Table 16-8.
SADDR – Slave Address Register
SADDR Address = 0A9H
Reset Value = 0000 0000B
Not Bit Addressable
Bit
7
6
5
4
3
2
1
0
Symbol
Function
SADDR7-0
UART Slave Address
When SM2 = 1, SADDR holds the 8-bit address for the UART multiprocessor communication mode. This address is
combined with SADEN to create the given and broadcast addresses for the device.
Table 16-9.
SADEN – Slave Address Mask Register
SADEN Address = 0B9H
Reset Value = 0000 0000B
Not Bit Addressable
Bit
7
6
5
4
3
2
1
0
Symbol
Function
SADEN7-0
UART Slave Address Mask
When SM2 = 1, SADEN holds the 8-bit address mask for the UART multiprocessor communication mode. This address
is combined with SADDR to create the given and broadcast addresses for the device.
16.5
More About Mode 0
In Mode 0, the UART is configured as a two wire half-duplex synchronous serial interface. In
two-wire mode serial data enters and exits through RXD and TXD outputs the shift clock. Eight
data bits are transmitted/received, with the LSB first. Figure 16-4 and Figure 16.6 on page 124
show simplified functional diagrams of the serial port in Mode 0 and associated timing. The baud
rate is programmable to 1/2 or 1/4 the system frequency by setting/clearing the SMOD1 bit in
Fast mode, or 1/3 or 1/6 the system frequency in Compatibility mode. However, changing
SMOD1 has an effect on the relationship between the clock and data as described below. The
baud rate can also be generated by Timer 1 by setting TB8 in SCON or the Internal Baud Rate
Generator by setting SRC in BDRCON. Table 16-10 lists the baud rate options for Mode 0.
Table 16-10. Mode 0 Baud Rates
120
SRC
TB8
SMOD1
Baud Rate (Fast)
Baud Rate (Compatibility)
0
0
0
fSYS/4
fSYS/6
0
0
1
fSYS/2
fSYS/3
0
1
0
(Timer 1 Overflow) / 4
(Timer 1 Overflow) / 4
0
1
1
(Timer 1 Overflow) / 2
(Timer 1 Overflow) / 2
1
X
0
(BRG Overflow) / 2
(BRG Overflow) / 2
1
X
1
BRG Overflow
BRG Overflow
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
16.5.1
Two-Wire (Half-Duplex) Mode
Transmission is initiated by any instruction that uses SBUF as a destination register. The “write
to SBUF” signal also loads a “1” into the 9th position of the transmit shift register and tells the TX
Control Block to begin a transmission. The internal timing is such that one full bit slot may elapse
between “write to SBUF” and activation of SEND.
SEND transfers the output of the shift register to the alternate output function line of P3.0, and
also transfers Shift Clock to the alternate output function line of P3.1. As data bits shift out to the
right, “0”s come in from the left. When the MSB of the data byte is at the output position of the
shift register, the “1” that was initially loaded into the 9th position is just to the left of the MSB,
and all positions to the left of that contain “0”s. This condition flags the TX Control block to do
one last shift, then deactivate SEND and set TI.
Reception is initiated by the condition REN = 1 and RI = 0. At the next clock cycle, the RX Control unit writes the bits 11111110B to the receive shift register and activates RECEIVE in the
next clock phase. RECEIVE enables Shift Clock to the alternate output function line of P3.1. As
data bits come in from the right, “1”s shift out to the left. When the “0” that was initially loaded
into the right-most position arrives at the left-most position in the shift register, it flags the RX
Control block to do one last shift and load SBUF. Then RECEIVE is cleared and RI is set.
The relationship between the shift clock and data is determined by the combination of the SM2
and SMOD1 bits as listed in Table 16-11 and shown in Figure . The SM2 bit determines the idle
state of the clock when not currently transmitting/receiving. The SMOD1 bit determines if the
output data is stable for both edges of the clock, or just one.
Table 16-11. Mode 0 Clock and Data Modes
SM2
SMOD1
Clock Idle
Data Changes
Data Sampled
0
0
High
While clock is high
Positive edge of clock
0
1
High
Negative edge of clock
Positive edge of clock
1
0
Low
While clock is low
Negative edge of clock
1
1
Low
Negative edge of clock
Positive edge of clock
In Two-Wire configuration Mode 0 may be used as a hardware accelerator for software emulation of serial interfaces such as a half-duplex Serial Peripheral Interface (SPI) master in mode
(0,0) or (1,1) or a Two-Wire Interface (TWI) in master mode. An example of Mode 0 emulating a
TWI master device is shown in Figure 16-3. In this example, the start, stop, and acknowledge
are handled in software while the byte transmission is done in hardware. Falling/rising edges on
TXD are created by setting/clearing SM2. Rising/falling edges on RXD are forced by setting/clearing the P3.0 register bit. SM2 and P3.0 must be 1 while the byte is being transferred.
Mode 0 transfers data LSB first whereas SPI or TWI are generally MSB first. Emulation of these
interfaces may require bit reversal of the transferred data bytes. The following code example
reverses the bits in the accumulator:
EX:
MOV
REVRS: RLC
XCH
RRC
XCH
DJNZ
R7, #8
A
A, R6
A
A, R6
R7, REVRS
; C << msb (ACC)
; msb (ACC) >> B
121
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 16-2. Mode 0 Waveforms (Two-Wire)
SMOD1 = 0
SM2 = 0
TXD
RXD (TX)
0
0
RXD (RX)
SMOD1 = 1
SM2 = 0
1
0
2
1
0
RXD (RX)
4
3
5
4
6
5
7
6
7
2
1
3
2
4
3
5
4
6
5
7
6
7
TXD
RXD (TX)
0
1
0
RXD (RX)
SMOD1 = 1
SM2 = 1
1
3
TXD
RXD (TX)
SMOD1 = 0
SM2 = 1
2
2
1
3
2
4
3
5
4
6
5
7
6
7
TXD
0
RXD (TX)
1
0
RXD (RX)
2
1
3
2
4
3
5
4
6
5
6
7
7
Figure 16-3. UART Mode 0 TWI Emulation (SMOD1 = 1)
(SCL) TXD
(SDA) RXD
0
1
2
3
4
5
6
7
ACK
SM2
P3.0
Sample ACK
Write to SBUF
TI
122
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 16-4. Serial Port Mode 0 (Two-Wire)
INTERNAL BUS
TIMER 1
OVERFLOW
1
“1“
f sys
0
TB8
2
2
0
1
SMOD1
SM2
INTERNAL BUS
WRITE TO SBUF
SEND
SHIFT
RXD (DATA OUT)
TXD (SHIFT CLOCK)
TI
WRITE TO SCON (CLEAR RI)
RI
RECEIVE
SHIFT
RXD (DATA IN)
TXD (SHIFT CLOCK)
123
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
16.6
More About Mode 1
Ten bits are transmitted (through TXD), or received (through RXD): a start bit (0), 8 data bits
(LSB first), and a stop bit (1). On receive, the stop bit goes into RB8 in SCON. In the
AT89LP51RD2/ED2/ID2, the baud rate is determined either by the Timer 1 overflow rate, the
TImer 2 overflow rate, or both. In this case one timer is for transmit and the other is for receive.
Figure 16-5 shows a simplified functional diagram of the serial port in Mode 1 and associated
timings for transmit and receive.
Transmission is initiated by any instruction that uses SBUF as a destination register. The “write
to SBUF” signal also loads a “1” into the 9th bit position of the transmit shift register and flags the
TX Control unit that a transmission is requested. Transmission actually commences at S1P1 of
the machine cycle following the next rollover in the divide-by-16 counter. Thus, the bit times are
synchronized to the divide-by-16 counter, not to the “write to SBUF” signal.
The transmission begins when SEND is activated, which puts the start bit at TXD. One bit time
later, DATA is activated, which enables the output bit of the transmit shift register to TXD. The
first shift pulse occurs one bit time after that.
As data bits shift out to the right, “0”s are clocked in from the left. When the MSB of the data byte
is at the output position of the shift register, the “1” that was initially loaded into the 9th position is
just to the left of the MSB, and all positions to the left of that contain “0”s. This condition flags the
TX Control unit to do one last shift, then deactivate SEND and set TI. This occurs at the tenth
divide-by-16 rollover after “write to SBUF.”
Reception is initiated by a 1-to-0 transition detected at RXD. For this purpose, RXD is sampled
at a rate of 16 times the established baud rate. When a transition is detected, the divide-by-16
counter is immediately reset, and 1FFH is written into the input shift register. Resetting the
divide-by-16 counter aligns its roll-overs with the boundaries of the incoming bit times.
The 16 states of the counter divide each bit time into 16ths. At the 7th, 8th, and 9th counter
states of each bit time, the bit detector samples the value of RXD. The value accepted is the
value that was seen in at least 2 of the 3 samples. This is done to reject noise. In order to reject
false bits, if the value accepted during the first bit time is not 0, the receive circuits are reset and
the unit continues looking for another 1-to-0 transition. If the start bit is valid, it is shifted into the
input shift register, and reception of the rest of the frame proceeds.
As data bits come in from the right, “1”s shift out to the left. When the start bit arrives at the leftmost position in the shift register, (which is a 9-bit register in Mode 1), it flags the RX Control
block to do one last shift, load SBUF and RB8, and set RI. The signal to load SBUF and RB8
and to set RI is generated if, and only if, the following conditions are met at the time the final shift
pulse is generated.
RI = 0 and
Either SM2 = 0, or the received stop bit = 1
If either of these two conditions is not met, the received frame is irretrievably lost. If both conditions are met, the stop bit goes into RB8, the 8 data bits go into SBUF, and RI is activated. At
this time, whether or not the above conditions are met, the unit continues looking for a 1-to-0
transition in RXD.
124
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 16-5. Serial Port Mode 1
TIMER 2
OVERFLOW
TIMER 1
OVERFLOW
INTERNAL BUS
“1”
WRITE
TO
SBUF
2
“0”
S
D Q
CL
“1”
SBUF
SMOD1
TXD
ZERO DETECTOR
“0”
“1”
SHIFT DATA
START
TX CONTROL
TCLK
16
SEND
TI
SERIAL
PORT
INTERRUPT
“1”
“0”
RX CLOCK
RCLK
16
SAMPLE
1-TO-0
TRANSITION
DETECTOR
RX CLOCK RI
START
RX CONTROL
LOAD
SBUF
SHIFT
1FFH
BIT
DETECTOR
INPUT SHIFT REG.
(9 BITS)
RXD
SHIFT
LOAD
SBUF
SBUF
READ
SBUF
INTERNAL BUS
TRANSMIT
TX
CLOCK
WRITE TO SBUF
SEND
DATA
SHIFT
D0
TXD
TI
RX
CLOCK
RECEIVE
D1
D2
D3
D4
D5
D6
D7
STOP BIT
START BIT
RXD
16 RESET
START BIT
D0
D1
D2
D3
D4
D5
D6
D7
STOP BIT
BIT DETECTOR SAMPLE TIMES
SHIFT
RI
125
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
16.7
More About Modes 2 and 3
Eleven bits are transmitted (through TXD), or received (through RXD): a start bit (0), 8 data bits
(LSB first), a programmable 9th data bit, and a stop bit (1). On transmit, the 9th data bit (TB8)
can be assigned the value of “0” or “1”. On receive, the 9th data bit goes into RB8 in SCON. The
baud rate is programmable to either 1/16 or 1/32 of the oscillator frequency in Mode 2. Mode 3
may have a variable baud rate generated from either Timer 1 or Timer 2, depending on the state
of RCLK and TCLK.
Figures 16-6 and 16-7 show a functional diagram of the serial port in Modes 2 and 3. The
receive portion is exactly the same as in Mode 1. The transmit portion differs from Mode 1 only
in the 9th bit of the transmit shift register.
Transmission is initiated by any instruction that uses SBUF as a destination register. The “write
to SBUF” signal also loads TB8 into the 9th bit position of the transmit shift register and flags the
TX Control unit that a transmission is requested. Transmission commences at S1P1 of the
machine cycle following the next rollover in the divide-by-16 counter. Thus, the bit times are synchronized to the divide-by-16 counter, not to the “write to SBUF” signal.
The transmission begins when SEND is activated, which puts the start bit at TXD. One bit time
later, DATA is activated, which enables the output bit of the transmit shift register to TXD. The
first shift pulse occurs one bit time after that. The first shift clocks a “1” (the stop bit) into the 9th
bit position of the shift register. Thereafter, only “0”s are clocked in. Thus, as data bits shift out to
the right, “0”s are clocked in from the left. When TB8 is at the output position of the shift register,
then the stop bit is just to the left of TB8, and all positions to the left of that contain “0”s. This condition flags the TX Control unit to do one last shift, then deactivate SEND and set TI. This occurs
at the 11th divide-by-16 rollover after “write to SBUF.”
Reception is initiated by a 1-to-0 transition detected at RXD. For this purpose, RXD is sampled
at a rate of 16 times the established baud rate. When a transition is detected, the divide-by-16
counter is immediately reset, and 1FFH is written to the input shift register.
At the 7th, 8th and 9th counter states of each bit time, the bit detector samples the value of RXD.
The value accepted is the value that was seen in at least 2 of the 3 samples. If the value
accepted during the first bit time is not 0, the receive circuits are reset and the unit continues
looking for another 1-to-0 transition. If the start bit proves valid, it is shifted into the input shift
register, and reception of the rest of the frame proceeds.
As data bits come in from the right, “1”s shift out to the left. When the start bit arrives at the leftmost position in the shift register (which in Modes 2 and 3 is a 9-bit register), it flags the RX Control block to do one last shift, load SBUF and RB8, and set RI. The signal to load SBUF and RB8
and to set RI is generated if, and only if, the following conditions are met at the time the final shift
pulse is generated:
RI = 0, and
Either SM2 = 0 or the received 9th data bit = 1
If either of these conditions is not met, the received frame is irretrievably lost, and RI is not set. If
both conditions are met, the received 9th data bit goes into RB8, and the first 8 data bits go into
SBUF. One bit time later, whether the above conditions were met or not, the unit continues looking for a 1-to-0 transition at the RXD input.
Note that the value of the received stop bit is irrelevant to SBUF, RB8, or RI.
126
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 16-6. Serial Port Mode 2
INTERNAL BUS
INTERNAL BUS
127
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 16-7. Serial Port Mode 3
TIMER 2
OVERFLOW
TIMER 1
OVERFLOW
INTERNAL BUS
TB8
WRITE
TO
SBUF
2
“0”
S
D Q
CL
“1”
SMOD1
SBUF
TXD
ZERO DETECTOR
“0”
“1”
TCLK
16
“0”
SHIFT DATA
START STOP BIT
TX CONTROL
RX CLOCK
SEND
TI
SERIAL
PORT
INTERRUPT
“1”
RCLK
16
SAMPLE
1-TO-0
TRANSITION
DETECTOR
RX CLOCK RI
START
RX CONTROL
LOAD
SBUF
SHIFT
1FFH
BIT
DETECTOR
INPUT SHIFT REG.
(9 BITS)
RXD
SHIFT
LOAD
SBUF
SBUF
READ
SBUF
INTERNAL BUS
TRANSMIT
TX
CLOCK
WRITE TO SBUF
SEND
DATA
SHIFT
D0
TXD
TI
D1
D2
D3
D4
D5
D6
D7
TB8
START BIT
STOP BIT
STOP BIT GEN
RX
CLOCK
RECEIVE
RXD
16 RESET
START BIT
D0
D1
BIT DETECTOR SAMPLE TIMES
D2
D3
D4
D5
D6
D7
RB8
STOP
BIT
SHIFT
RI
128
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
17. Enhanced Serial Peripheral Interface
The Serial Peripheral Interface (SPI) allows high-speed, full-duplex synchronous data transfer
between the AT89LP51RD2/ED2/ID2 and peripheral devices or between multiple microcontroller devices, including multiple masters and slaves on a single bus. The SPI includes the
following features:
• Full-duplex, 3-wire or 4-wire Synchronous Data Transfer
• Master or Slave Operation
• Maximum Bit Frequency = fSYS/2
• LSB First or MSB First Data Transfer
• Seven Programmable Bit Rates or Timer 1-based Baud Generation (Master Mode)
• End of Transmission Interrupt Flag
• Write Collision Flag Protection
• Double-buffered Receive and Transmit
• Transmit Buffer Empty Interrupt Flag
• Mode Fault (Master Collision) Detection and Interrupt
• Wake up from Idle Mode
A block diagram of the SPI is shown below in Figure 17-1.
Figure 17-1. SPI Block Diagram
MSB
FPERIPH
LSB
S
MISO
M
M
MOSI
S
Pin Control Logic
8-bit Shift Register
Read Data Buffer
7-bit Divider
Write Data Buffer
T1 OVF
SPI Clock (Master)
SPR0
SPI Status Register
DORD
SPR0
SPR1
CPHA
CPOL
MSTR
SSDIS
SPI Control Register
8
SPI Interrupt
Request
SPEN
8
SPR2
MSTR
SPEN
TBIE
DORD
REMAP
TXE
MODF
WCOL
SSERR
SPEN
MSTR
SPR1
SPR2
M
SS
SPI Control
SPIF
SCK
S
Clock
Logic
Clock Select
8
Internal
Data Bus
129
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
17.1
Interface Description
The interconnection between master and slave devices with SPI is shown in Figure . The four
pins in the interface are Master-In/Slave-Out (MISO), Master-Out/Slave-In (MOSI), Serial Clock
(SCK), and Slave Select (SS). The MSTR bit in SPCON determines the directions of MISO and
MOSI. Also notice that MOSI connects to MOSI and MISO to MISO. By default SS is an input to
both master and slave devices. The master must drive the SS input of each slave device
independently.
Figure 17-2. SPI Master-Slave Interconnection
Master
MSB
LSB
Slave
MSB
MISO
LSB
MISO
8-Bit Shift Register
8-Bit Shift Register
MOSI
MOSI
SSDIS
VCC
SS
MODF
SS
GPIO
Clock
Generator
SSDIS
SCK
SCK
The location of the SPI pins is determined by the REMAP bit in SPSTA as shown in Table 17-1.
When REMAP = 0, the pins are located in the same locations on Port 1 as the
AT89C51RD2/ED2/ID2. When REMAP = 1 the pins are shuffled on Port 1 to be compatible with
AT89S8253 and AT89LP6440. Note that the SPI-based In-System Programming (ISP) interface
always uses the REMAP = 1 pins regardless of the REMAP setting.
Table 17-1.
Serial Peripheral Interface Connections
Pin Connection
17.1.1
Name
Function
SCK
Direction
REMAP = 0
REMAP = 1
MSTR = 1
MSTR = 0
Serial Clock
P1.6
P1.7
OUT
IN
MISO
Master In / Slave Out
P1.5
P1.6
IN
OUT
MOSI
Master Out / Slave In
P1.7
P1.5
OUT
IN
SS
Slave Select (Active-Low)
P1.1
P1.4
IN
IN
SPI Serial Clock (SCK)
This signal is used to synchronize the data movement both in and out of the devices through
their MOSI and MISO lines. The SCK line is shared among all devices on the bus. It is driven by
the master for eight clock cycles to exchange one byte on the serial lines. The SCK pin is a clock
output in master mode and a clock input in slave mode. If multiple masters are present in a system, only one should drive the SCK line at a time.
In master mode, the baud rate of SCK is determined by the SPR bits in SPCON. The SPR bits
select a value from a 7-bit prescaler on the system clock or the Timer 1 overflow. In slave mode
the clock rate is set by the master device; the slave need not
130
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
17.1.2
Master Output / Slave Input (MOSI)
This 1-bit signal is directly connected between the master device and all slave devices. The
MOSI line is used to transfer data in series from the master to the slave. Therefore, it is an output signal from the master, and an input signal to a slave. A byte (8-bit word) is normally
transmitted most significant bit (MSB) first, least significant bit (LSB) last. The DORD bit in
SPSTA can change the data ordering to LSB first and MSB last. All devices on the same bus
should share the same data order. If multiple masters are present in a system, only one should
drive the MOSI line at a time.
17.1.3
Master Input / Slave Output (MISO)
This 1-bit signal is directly connected between all slave devices and a master device. The MISO
line is used to transfer data in series from a slave to the master. Therefore, it is an output signal
from the slave, and an input signal to the master. A byte (8-bit word) is transmitted most significant bit (MSB) first, least significant bit (LSB) last. The DORD bit in SPSTA can change the data
ordering to LSB first anf MSB last. All devices on the same bus should share the same data
order. When multiple slaves are present in a system, only the slave with its SS input low will
drive MISO.
17.1.4
Slave Select (SS)
Each slave peripheral is selected by one Slave Select pin (SS). This signal must stay low for any
message for a slave. It is obvious that only one master can drive the network at a time. The master may select each slave device by software through port pins. To prevent bus conflicts on the
MISO line, only one slave should be selected at a time by the master for a transmission.
In a master configuration, the SS line can be used in conjunction with the MODF flag in the SPI
Status register (SPSTA) to prevent multiple masters from driving MOSI and SCK (see Error
conditions).
A high level on the SS pin puts the MISO line of a Slave SPI in a high-impedance state.
The SS pin can be used as a general-purpose I/O if the following conditions are met:
• The device is configured as a Master and the SSDIS control bit in SPCON is set. This kind of
configuration can be found when only one Master is driving the network and there is no way
that the SS pin could be pulled low. Therefore, the MODF flag in the SPSTA will never be
set(1).
• The Device is configured as a Slave with CPHA and SSDIS control bits set(2). This kind of
configuration can happen when the system comprises one Master and one Slave only.
Therefore, the device should always be selected and there is no reason that the Master uses
the SS pin to select the communicating Slave device.
Note:
1. Clearing SSDIS control bit does not clear MODF.
2. Special care should be taken when setting SSDIS control bit when CPHA = ’0’ because in this
mode the SS is used to start the transmission on some devices. This requirement does not
apply to the AT89LP51RD2/ED2/ID2 itself.
The In-System Programming (ISP) interface also uses the SPI pins. Although the ISP protocol is
SPI-based, the SS pin has special meaning and must be driven by the master as a frame delimiter. SS cannot be tied to ground for ISP to function correctly.
When the SPI is configured as a Master (MSTR in SPCON is set), the operation of the SS pin
depends on the setting of the Slave Select Disable bit, SSDIS. If SSDIS = 1, the SS pin is a general purpose output pin which does not affect the SPI system. Typically, the pin will be driving
the SS pin of an SPI Slave. If SSDIS = 0, SS must be held high to ensure Master SPI operation.
131
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
If the SS pin is driven low by peripheral circuitry when the SPI is configured as a Master with
SSIG = 0, the SPI system interprets this as another master selecting the SPI as a slave and
starting to send data to it. To avoid bus contention, the SPI system takes the following actions:
1. The MSTR bit in SPCON is cleared and the SPI system becomes a Slave. As a result
of the SPI becoming a Slave, the MOSI and SCK pins become inputs.
2. The MODF Flag in SPSTA is set, and if the SPI interrupt is enabled, the interrupt routine will be executed.
Thus, when interrupt-driven SPI transmission is used in Master mode, and there exists a possibility that SS may be driven low, the interrupt should always check that the MSTR bit is still set. If
the MSTR bit has been cleared by a slave select, it must be set by the user to re-enable SPI
Master mode.
17.1.5
Pin Configuration
When the SPI is enabled (SPEN = 1), the data direction of the MOSI, MISO and SCK pins is
automatically overridden according to the MSTR bit as shown in Table 17-2. The user need not
reconfigure the pins when switching from master to slave or vice-versa. For more details on port
configuration, refer to “Port Configuration” on page 73.
.
Table 17-2.
Pin
SPI Pin Configuration and Behavior when SPE = 1
Mode
Master (MSTR = 1)
Slave (MSTR = 0)
Quasi-bidirectional
Output
Input (Internal Pull-up)
Push-Pull Output
Output
Input (Tristate)
Input-Only
No output (Tristated)
Input (Tristate)
Open-Drain Output
Output
Input (External Pull-up)
SCK
Quasi-bidirectional
(1)
Input (Internal Pull-up)
(2)
Output
Push-Pull Output
Output
Input (Tristate)
Input-Only
No output (Tristated)
Input (Tristate)
MOSI
(1)
Input (External Pull-up)
Open-Drain Output
Output
Quasi-bidirectional
Input (Internal Pull-up)
Output (SS = 0)
Internal Pull-up (SS = 1)
Push-Pull Output
Input (Tristate)
Output (SS = 0)
Tristated (SS = 1)
Input-Only
Input (Tristate)
No output (Tristated)
Open-Drain Output
Input (External Pull-up)
Output (SS = 0)
External Pull-up (SS = 1)
MISO
Notes:
1. In these modes MOSI is active only during transfers. MOSI will be pulled high between transfers to allow other masters to control the line.
2. In Push-Pull mode MOSI is active only during transfers, otherwise it is tristated to prevent line
contention. A weak external pull-up may be required to prevent MOSI from floating.
132
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
17.2
Master Operation
An SPI master device initiates all data transfers on the SPI bus. The AT89LP51RD2/ED2/ID2 is
configured for master operation by setting MSTR = 1 in SPCON. Writing to the SPI data register
(SPDAT) while in master mode loads the transmit buffer. If the SPI shift register is empty, the
byte in the transmit buffer is moved to the shift register; the transmit buffer empty flag, TXE, is
set; and a transmission begins. The transfer may start after an initial delay, while the clock generator waits for the next full bit slot of the specified baud rate. The master shifts the data out
serially on the MOSI line while providing the serial shift clock on SCK. When the transfer finishes, the SPIF flag is set to “1” and an interrupt request is generated, if enabled. The data
received from the addressed SPI slave device is also transferred from the shift register to the
receive buffer. Therefore, the SPIF bit flags both the transmit-complete and receive-data-ready
conditions. The received data is accessed by reading SPDAT.
While the TXE flag is set, the transmit buffer is empty. TXE can be cleared by software or by
writing to SPDAT. Writing to SPDAT will clear TXE and load the transmit buffer. The user may
load the buffer while the shift register is busy, i.e. before the current transfer completes. When
the current transfer completes, the queued byte in the transmit buffer is moved to the shift register and the next transfer commences. TXE will generate an interrupt if the SPI interrupt is
enabled and if the ENH bit in SPSTA is set. For multi-byte transfers, TXE may be used to
remove any dead time between byte transmissions.
The SPI master can operate in two modes: multi-master mode and single-master mode. By
default, multi-master mode is active when SSIG = 0. In this mode, the SS input is used to disable a master device when another master is accessing the bus. When SS is driven low, the
master device becomes a slave by clearing its MSTR bit and a Mode Fault is generated by setting the MODF bit in SPSTA. MODF will generate an interrupt if enabled. The MSTR bit must be
set in software before the device may become a master again. Single-master mode is enabled
by setting SSIG = 1. In this mode SS is ignored and the master is always active. SS may be
used as a general purpose I/O in this mode.
17.3
Slave Operation
When the AT89LP51RD2/ED2/ID2 is not configured for master operation, MSTR = 0, it will operate as an SPI slave. In slave mode, bytes are shifted in through MOSI and out through MISO by
a master device controlling the serial clock on SCK. When a byte has been transferred, the SPIF
flag is set to “1” and an interrupt request is generated, if enabled. The data received from the
addressed master device is also transferred from the shift register to the receive buffer. The
received data is accessed by reading SPDAT. A slave device cannot initiate transfers. Data to
be transferred to the master device must be preloaded by writing to SPDAT. Writes to SPDAT
are double-buffered. The transmit buffer is loaded first and if the shift register is empty, the contents of the buffer will be transferred to the shift register.
While the TXE flag is set, the transmit buffer is empty. TXE can be cleared by software or by
writing to SPDAT. Writing to SPDAT will clear TXE and load the transmit buffer. The user may
load the buffer while the shift register is busy, i.e. before the current transfer completes. When
the current transfer completes, the queued byte in the transmit buffer is moved to the shift register and waits for the master to initiate another transfer. TXE will generate an interrupt if the SPI
interrupt is enabled and if the ENH bit in SPSTA is set.
The SPI slave can operate in two modes: 4-wire mode and 3-wire mode. By default, 4-wire
mode is active when SSIG = 0. In this mode, the SS input is used to enable/disable the slave
device when addressed by a master. When SS is driven low, the slave device is enabled and will
133
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
shift out data on MISO in response to the serial clock on SCK. While SS is high, the SPI slave
will remain sleeping with MISO inactive. Three-wire mode is enabled by setting SSIG = 1. In this
mode SS is ignored and the slave is always active. SS may be used as a general purpose I/O in
this mode.
The Disable Slave Output bit, DISSO in SPSTA, may be used to disable the MISO line of a slave
device. DISSO can allow several slave devices to share MISO while operating in 3-wire mode. In
this case some protocol other than SS may be used to determine which slave is enabled.
17.4
Error Conditions
The following flags in the SPSTA signal SPI error conditions:
17.4.1
Mode Fault (MODF)
Mode Fault error in Master mode SPI indicates that the level on the Slave Select (SS) pin is
inconsistent with the actual mode of the device. MODF is set to warn that there may be a multimaster conflict for system control. In this case, the SPI system is affected in the following ways:
• An SPI receiver/error CPU interrupt request is generated
• The SPEN bit in SPCON is cleared. This disables the SPI
• The MSTR bit in SPCON is cleared
When SS Disable (SSDIS) bit in the SPCON register is cleared, the MODF flag is set when the
SS signal becomes ’0’.
However, as stated before, for a system with one Master, if the SS pin of the Master device is
pulled low, there is no way that another Master attempts to drive the network. In this case, to
prevent the MODF flag from being set, software can set the SSDIS bit in the SPCON register
and therefore making the SS pin as a general-purpose I/O pin.
Clearing the MODF bit is accomplished by a read of SPSTA register with MODF bit set, followed
by a write to the SPCON register. SPEN Control bit may be restored to its original set state after
the MODF bit has been cleared.
17.4.2
Write Collision (WCOL)
A Write Collision (WCOL) flag in the SPSTA is set when a write to the SPDAT register is done
during a transmit sequence.
WCOL does not cause an interruption, and the transfer continues uninterrupted.
Clearing the WCOL bit is done through a software sequence of an access to SPSTA and an
access to SPDAT.
17.4.3
Overrun Condition
An overrun condition occurs when the Master device tries to send several data Bytes and the
Slave devise has not cleared the SPIF bit issuing from the previous data Byte transmitted. In this
case, the receiver buffer contains the Byte sent after the SPIF bit was last cleared. A read of the
SPDAT returns this Byte. All others Bytes are lost.
This condition is not detected by the SPI peripheral.
134
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
17.4.4
17.5
SS Error Flag (SSERR)
A Synchronous Serial Slave Error occurs when SS goes high before the end of a received data
in slave mode. SSERR does not cause in interruption, this bit is cleared by writing 0 to SPEN bit
(reset of the SPI state machine).
Serial Clock Timing
The CPHA, CPOL and SPR bits in SPCON control the shape and rate of SCK. The two SPR bits
provide four possible clock rates when the SPI is in master mode. In slave mode, the SPI will
operate at the rate of the incoming SCK as long as it does not exceed the maximum bit rate.
There are also four possible combinations of SCK phase and polarity with respect to the serial
data. CPHA and CPOL determine which format is used for transmission. The SPI data transfer
formats are shown in Figures 17-3 and 17-4. To prevent glitches on SCK from disrupting the
interface, CPHA, CPOL, and SPR should not be modified while the interface is enabled, and the
master device should be enabled before the slave device(s).
Figure 17-3. SPI Transfer Format with CPHA = 0
Note:
*Not defined but normally MSB of character just received.
Figure 17-4. SPI Transfer Format with CPHA = 1
SCK CYCLE #
(FOR REFERENCE)
1
2
3
4
5
6
7
8
SCK (CPOL = 0)
SCK (CPOL = 1)
MOSI
(FROM MASTER)
MISO
(FROM SLAVE)
*
MSB
6
5
4
3
2
1
MSB
6
5
4
3
2
1
LSB
LSB
SS (TO SLAVE)
Note:
*Not defined but normally LSB of previously transmitted character.
135
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
17.6
Registers
Table 17-3.
SPCON – SPI Control Register
SPCON Address = C3H
Reset Value = 0001 0100B
Not Bit Addressable
Bit
SPR2
SPEN
SSDIS
MSTR
CPOL
CPHA
SPR1
SPR0
7
6
5
4
3
2
1
0
Symbol
Function
SPR2
Serial Peripheral Clock Rate 2
See the description for SPR1-0
SPEN
Serial peripheral Enable
SPI = 1 enables the SPI channel and connects SS, MOSI, MISO and SCK to pins P1.4, P1.5, P1.6, and P1.7. SPI = 0
disables the SPI channel.
SSDIS
Slave Select Disable
If SSDIS = 0, the SPI will only operate in slave mode if SS (P1.4) is pulled low. When SSDIS = 1, the SPI ignores SS in
slave mode and is active whenever SPE (SPCON.6) is set. When MSTR = 1 and SSDIS = 0, SS is monitored for master
mode collisions. Setting SSDIS = 1 will ignore collisions on SS. P1.4 may be used as a regular I/O pin when SSIG = 1.
MSTR
Master/Slave Select
MSTR = 1 selects Master SPI mode. MSTR = 0 selects slave SPI mode.
CPOL
Clock Polarity
When CPOL = 1, SCK is high when idle. When CPOL = 0, SCK of the master device is low when not transmitting. Please
refer to figure on SPI clock phase and polarity control.
CPHA
Clock Phase
The CPHA bit together with the CPOL bit controls the clock and data relationship between master and slave. Please refer
to figure on SPI clock phase and polarity control.
Serial Peripheral Clock Rate
These two bits control the SCK rate of the device configured as master. SPR1 and SPR0 have no effect on the slave. The
relationship between SCK and the oscillator frequency, FOSC., is as follows:
SPR1
SPR0
Notes:
SPR2
SPR1
SPR0
SCK (TSCK = 0)
0
0
0
fPERIPH/2
0
0
1
fPERIPH/4
0
1
0
fPERIPH/8
0
1
1
fPERIPH/16
1
0
0
fPERIPH/32
1
0
1
fPERIPH/64
1
1
0
fPERIPH/128
1
1
1
Timer 1 Overflow/2
1. Set up the clock mode before enabling the SPI: set all bits needed in SPCON except the SPEN bit, then set SPEN.
2. Enable the master SPI prior to the slave device.
3. Slave echoes master on the next Tx if not loaded with new data.
136
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 17-4.
SPDAT – SPI Data Register
SPDAT Address = C5H
Reset Value = 0000 0000
Not Bit Addressable
Bit
Table 17-5.
SPD7
SPD6
SPD5
SPD4
SPD3
SPD2
SPD1
SPD0
7
6
5
4
3
2
1
0
SPSTA – SPI Status Register
SPSTA Address = C4H
Reset Value = 0000 0000B
Not Bit Addressable
Bit
SPIF
WCOL
SSERR
MODF
TXE
DORD
REMAP
TBIE
7
6
5
4
3
2
1
0
Symbol
Function
SPIF
SPI Transfer Complete Interrupt Flag
When a serial transfer is complete, the SPIF bit is set by hardware and an interrupt is generated if ESP = 1. The SPIF bit
may be cleared by software or by reading the SPI status register followed by reading/writing the SPI data register.
WCOL
Write Collision Flag
The WCOL bit is set by hardware if SPDAT is written while the transmit buffer is full. The ongoing transfer is not affected.
WCOL may be cleared by software or by reading the SPI status register followed by reading/writing the SPI data register.
SSERR
SS Slave Error Flag
Set by hardware when SS is deasserted before the end of a received data byte.
MODF
Mode Fault Flag
MODF is set by hardware when a master mode collision is detected (MSTR = 1, SSIG = 0 and SS = 0) and an interrupt
is generated if ESP = 1. MODF must be cleared by software.
TXE
Transmit Buffer Empty Flag
Set by hardware when the transmit buffer is loaded into the shift register, allowing a new byte to be loaded. TXE must be
cleared by software. When ENH = 1 and ESP = 1, TXE will generate an interrupt.
DORD
Data order
DORD = 1 selects LSB first data transmission. DORD = 0 selects MSB first data transmission.
REMAP
Remap SPI Pins
When cleared the SPI pins are in the default locations on Port 1 that are compatible with AT89C51RD2/ED2/ID2. When
set the pins are shuffled on Port 1 to match the AT89S8253 or AT89LP6440 devices. See Table 17-1.
TBIE
TX Buffer Interrupt Enable
When TBIE = 1, TXE will generate an SPI interrupt if ESP = 1. When TBIE = 0, TXE does not generate an interrupt.
137
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
18. Two-Wire Serial Interface
The Two-Wire Interface (TWI) is a bi-directional 2-wire serial communication standard. It is
designed primarily for simple but efficient integrated circuit (IC) control. The system is comprised
of two lines, SCL (Serial Clock) and SDA (Serial Data) that carry information between the ICs
connected to them. The only external hardware needed to implement the bus is a single pull-up
resistor for each of the TWI bus lines. All devices connected to the bus have individual
addresses, and mechanisms for resolving bus contention are inherent in the TWI protocol. The
serial data transfer is limited to 400Kbit/s in standard mode. Various communication configurations can be designed using this bus. Figure 18-1 shows a typical 2-wire bus configuration. Any
of the devices connected to the bus can be master or slave.
The Two-Wire Interface on the AT89LP51RD2/ED2/ID2 provides the following features:
• Simple Yet Powerful and Flexible Communication Interface, only two Bus Lines Needed
• Both Master and Slave Operation Supported
• Device can Operate as Transmitter or Receiver
• 7-bit Address Space Allows up to 128 Different Slave Addresses
• Multi-master Arbitration Support
• Up to 400 kHz Data Transfer Speed
• Fully Programmable Slave Address with General Call Support
Note:
The TWI is available on both the AT89LP51RD2 and AT89LP51ED2 where as it was not available
on the AT89C51RD2 and AT89C51ED2. The TWI is not available in the PDIP package.
Figure 18-1. Two-Wire Bus Configuration
VCC
Device 1
Device 2
Device 3
........
Device n
R1
R2
SDA
SCL
As depicted in Figure 18-1, both bus lines are connected to the positive supply voltage through
pull-up resistors. The bus drivers of all TWI-compliant devices are open-drain or open-collector.
This implements a wired-AND function which is essential to the operation of the interface. A low
level on a TWI bus line is generated when one or more TWI devices output a zero. A high level
is output when all TWI devices tristate their outputs, allowing the pull-up resistors to pull the line
high. Note that all AT89LP devices connected to the TWI bus must be powered in order to allow
any bus operation. The number of devices that can be connected to the bus is only limited by the
bus capacitance limit of 400 pF and the 7-bit slave address space.
138
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
18.1
18.1.1
Data Transfer and Frame Format
Transferring Bits
Each data bit transferred on the TWI bus is accompanied by a pulse on the clock line. The level
of the data line must be stable when the clock line is high. The only exception to this rule is for
generating start and stop conditions.
Figure 18-2. Data Validity
SDA
SCL
Data Stable
Data Stable
Data Change
18.1.2
START and STOP Conditions
The Master initiates and terminates a data transmission. The transmission is initiated when the
Master issues a START condition on the bus, and it is terminated when the Master issues a
STOP condition. Between a START and a STOP condition, the bus is considered busy, and no
other Master should try to seize control of the bus. A special case occurs when a new START
condition is issued between a START and STOP condition. This is referred to as a REPEATED
START condition, and is used when the Master wishes to initiate a new transfer without relinquishing control of the bus. After a REPEATED START, the bus is considered busy until the next
STOP. This is identical to the START behavior, and therefore START is used to describe both
START and REPEATED START for the remainder of this data sheet, unless otherwise noted.
As depicted below, START and STOP conditions are signalled by changing the level of the SDA
line when the SCL line is high.
Figure 18-3. START, REPEATED START, and STOP Conditions
SDA
SCL
START
18.1.3
STOP START
REPEATED START
STOP
Address Packet Format
All address packets transmitted on the TWI bus are nine bits long, consisting of seven address
bits, one READ/WRITE control bit and an acknowledge bit. If the READ/WRITE bit is set, a read
operation is to be performed, otherwise a write operation should be performed. When a slave
recognizes that it is being addressed, it should acknowledge by pulling SDA low in the ninth SCL
(ACK) cycle. If the addressed Slave is busy, or for some other reason can not service the Mas139
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
ter’s request, the SDA line should be left high in the ACK clock cycle. The Master can then
transmit a STOP condition, or a REPEATED START condition to initiate a new transmission. An
address packet consisting of a slave address and a READ or a WRITE bit is called SLA+R or
SLA+W, respectively.
The MSB of the address byte is transmitted first. Slave addresses can freely be allocated by the
designer, but the address 0000 000 is reserved for a general call.
When a general call is issued, all slaves should respond by pulling the SDA line low in the ACK
cycle. A general call is used when a Master wishes to transmit the same message to several
slaves in the system. When the general call address followed by a write bit is transmitted on the
bus, all slaves set up to acknowledge the general call will pull the SDA line low in the ACK cycle.
The following data packets will then be received by all the slaves that acknowledged the general
call. Note that transmitting the general call address followed by a Read bit is meaningless, as
this would cause contention if several slaves started transmitting different data.
All addresses of the format 1111 xxx should be reserved for future purposes.
Figure 18-4. Address Packet Format
Addr MSB
Addr LSB
R/W
ACK
7
8
9
SDA
SCL
1
2
START
18.1.4
Data Packet Format
All data packets transmitted on the TWI bus are nine bits long, consisting of one data byte and
an acknowledge bit. During a data transfer, the Master generates the clock and the START and
STOP conditions, while the Receiver is responsible for acknowledging the reception. An
Acknowledge (ACK) is signalled by the Receiver pulling the SDA line low during the ninth SCL
cycle. If the Receiver leaves the SDA line high, a NACK is signalled. When the Receiver has
received the last byte, or for some reason cannot receive any more bytes, it should inform the
Transmitter by sending a NACK after the final byte. The MSB of the data byte is transmitted first.
Figure 18-5. Data Packet Format
Data MSB
Data LSB
ACK
8
9
Aggregate
SDA
SDA from
Transmitter
SDA from
Receiver
SCL from
Master
1
SLA+R/W
140
2
7
Data Byte
STOP, REPEATED
START, or Next
Data Byte
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
18.1.5
Combining Address and Data Packets Into a Transmission
A transmission basically consists of a START condition, a SLA+R/W, one or more data packets
and a STOP condition. An empty message, consisting of a START followed by a STOP condition, is illegal. Note that the wired-ANDing of the SCL line can be used to implement
handshaking between the Master and the Slave. The Slave can extend the SCL low period by
pulling the SCL line low. This is useful if the clock speed set up by the Master is too fast for the
Slave, or the Slave needs extra time for processing between the data transmissions. The Slave
extending the SCL low period will not affect the SCL high period, which is determined by the
Master. As a consequence, the Slave can reduce the TWI data transfer speed by prolonging the
SCL duty cycle.
Figure 18-6 shows a typical data transmission. Note that several data bytes can be transmitted
between the SLA+R/W and the STOP condition, depending on the software protocol implemented by the application software.
Figure 18-6. Typical Data Transmission
Addr MSB
Addr LSB
R/W
ACK
Data MSB
7
8
9
1
Data LSB
ACK
8
9
SDA
SCL
1
START
18.2
2
SLA+R/W
2
7
Data Byte
STOP
Multi-master Bus Systems, Arbitration and Synchronization
The TWI protocol allows bus systems with several masters. Special concerns have been taken
in order to ensure that transmissions will proceed as normal, even if two or more masters initiate
a transmission at the same time. Two problems arise in multi-master systems:
• An algorithm must be implemented allowing only one of the masters to complete the
transmission. All other masters should cease transmission when they discover that they have
lost the selection process. This selection process is called arbitration. When a contending
master discovers that it has lost the arbitration process, it should immediately switch to Slave
mode to check whether it is being addressed by the winning master. The fact that multiple
masters have started transmission at the same time should not be detectable to the slaves
(i.e., the data being transferred on the bus must not be corrupted).
• Different masters may use different SCL frequencies. A scheme must be devised to
synchronize the serial clocks from all masters, in order to let the transmission proceed in a
lockstep fashion. This will facilitate the arbitration process.
The wired-ANDing of the bus lines is used to solve both these problems. The serial clocks from
all masters will be wired-ANDed, yielding a combined clock with a high period equal to the one
from the master with the shortest high period. The low period of the combined clock is equal to
the low period of the master with the longest low period. Note that all masters listen to the SCL
line, effectively starting to count their SCL high and low Time-out periods when the combined
SCL line goes high or low, respectively.
141
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 18-7. SCL Synchronization between Multiple Masters
TA low
TA high
SCL from
Master A
SCL from
Master B
SCL bus
Line
TBlow
TBhigh
Masters Start
Counting Low Period
Masters Start
Counting High Period
Arbitration is carried out by all masters continuously monitoring the SDA line after outputting
data. If the value read from the SDA line does not match the value the master had output, it has
lost the arbitration. Note that a master can only lose arbitration when it outputs a high SDA value
while another master outputs a low value. The losing master should immediately go to Slave
mode, checking if it is being addressed by the winning master. The SDA line should be left high,
but losing masters are allowed to generate a clock signal until the end of the current data or
address packet. Arbitration will continue until only one master remains, and this may take many
bits. If several masters are trying to address the same slave, arbitration will continue into the
data packet.
Figure 18-8. Arbitration between Two Masters
START
Master A Loses
Arbitration, SDAA SDA
SDA from
Master A
SDA from
M
SDA Line
Synchronized
SCL Line
Note that arbitration is not allowed between:
• A REPEATED START condition and a data bit.
• A STOP condition and a data bit.
• A REPEATED START and a STOP condition.
142
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
It is the user software’s responsibility to ensure that these illegal arbitration conditions never
occur. This implies that in multi-master systems, all data transfers must use the same composition of SLA+R/W and data packets. In other words: All transmissions must contain the same
number of data packets, otherwise the result of the arbitration is undefined.
18.3
Overview of the TWI Module
The TWI module is comprised of several submodules, as shown in Figure 18-9. All registers
drawn in a thick line are accessible through the AT89LP data bus.
Figure 18-9. Overview of the TWI Module
Slew-rate
Control
SDA
Spike
Filter
Slew-rate
Control
Spike
Filter
Bus Interface Unit
START / STOP
Control
Spike Suppression
Arbitration Detection
Address/Data Shift
Register (SSDAT)
Address Match Unit
Address Register
(SSADR)
Address Comparator
Bit Rate Generator
Prescaler
Ack
Timer 1 Overflow
Control Unit
Status Register
(SSCS)
Control Register
(SSCON)
TWI Unit
SCL
State Machine and
Status Control
18.3.1
SCL and SDA Pins
These pins interface the TWI with the rest of the MCU system. The output drivers contain a slewrate limiter in order to conform to the TWI specification. The input stages contain a spike suppression unit removing spikes shorter than 50 ns.
18.3.2
Bit Rate Generator Unit
This unit controls the period of SCL when operating in a Master mode. The SCL period is controlled by settings in the SSCON register. Slave operation does not depend on the Bit Rate
setting, but the CPU clock frequency in the slave must be at least 16 times higher than the SCL
frequency. Note that slaves may prolong the SCL low period, thereby reducing the average TWI
bus clock period. The SCL frequency is generated according to Table 18-1.
143
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 18-1.
18.3.3
TWI Bit Rate Configuration
Bit Rate (kHz)
CR2
CR1
CR0
FOSCA
Division
0
0
0
256
47
62.5
0
0
1
224
53.5
71.5
0
1
0
192
62.5
83
0
1
1
160
75
100
1
0
0
Unused
1
0
1
120
100
133.3
1
1
0
60
200
266.6
1
1
1
96 x Timer 1
Overflow
0.5 < baud < 62.5
0.67 < baud < 83
FOSCA = 12 MHz
FOSCA = 16 MHz
Bus Interface Unit
This unit contains the Data and Address Shift Register (SSDAT), a START/STOP Controller and
Arbitration detection hardware. The SSDAT contains the address or data bytes to be transmitted, or the address or data bytes received. In addition to the 8-bit SSDAT, the Bus Interface Unit
also contains a register containing the (N)ACK bit to be transmitted or received. This (N)ACK
Register is not directly accessible by the application software. However, when receiving, it can
be set or cleared by manipulating the TWI Control Register (SSCON). When in Transmitter
mode, the value of the received (N)ACK bit can be determined by the value in the SSCS. The
START/STOP Controller is responsible for generation and detection of START, REPEATED
START, and STOP conditions.
If the TWI has initiated a transmission as Master, the Arbitration Detection hardware continuously monitors the transmission trying to determine if arbitration is in process. If the TWI has lost
an arbitration, the Control Unit is informed. Correct action can then be taken and appropriate
status codes generated.
18.3.4
Address Match Unit
The Address Match unit checks if received address bytes match the 7-bit address in the TWI
Address Register (SSADR). If the TWI General Call Recognition Enable (GC) bit in the SSADR
is written to one, all incoming address bits will also be compared against the General Call
address. Upon an address match, the Control unit is informed, allowing correct action to be
taken. The TWI may or may not acknowledge its address, depending on settings in the SSCON.
18.3.5
Control Unit
The Control unit monitors the TWI bus and generates responses corresponding to settings in the
TWI Control Register (SSCON). When an event requiring the attention of the application occurs
on the TWI bus, the TWI Interrupt Flag (SI) is asserted. In the next clock cycle, the TWI Status
Register (SSCS) is updated with a status code identifying the event. The SSCS only contains
relevant status information when the TWI interrupt flag is asserted. At all other times, the SSCS
contains a special status code indicating that no relevant status information is available. As long
as the SI flag is set, the SCL line is held low. This allows the application software to complete its
tasks before allowing the TWI transmission to continue.
The SI flag is set in the following situations:
144
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
• After the TWI has transmitted a START/REPEATED START condition.
• After the TWI has transmitted SLA+R/W.
• After the TWI has transmitted an address byte.
• After the TWI has lost arbitration.
• After the TWI has been addressed by own slave address or general call.
• After the TWI has received a data byte.
• After a STOP or REPEATED START has been received while still addressed as a Slave.
• When a bus error has occurred due to an illegal START or STOP condition.
18.4
Register Overview
Table 18-2.
SSCON – Two-Wire Control Register
SSCON Address = AAH
Reset Value = X000 00XXB
Not Bit Addressable
Bit
CR2
SSIE
STA
STO
SI
AA
CR1
CR0
7
6
5
4
3
2
1
0
Symbol
Function
CR2
Bit Control Rate 2
Sets the bit rate for TWI master mode along with C1 and CR0. See Table 18-1.
SSIE
Two-wire Serial Interface Enable
Set to enable the TWI. Clear to disable the TWI.
STA
Start Flag
Set to send a START condition on the bus. Must be cleared by software.
STO
Stop Flag
Set to send a STOP condition on the bus. Cleared automatically by hardware when the STOP occurs.
SI
Two-wire Interface Interrupt Flag
Set by hardware when the TWI requests an interrupt. SI must be cleared by software. While SI is set, the SCL low period
is stretched. Note that clearing this flag starts the operation of the TWI, so all accesses to the other TWI registers
(SSADR, SSCS and SSDAT) must be complete before clearing this flag.
AA
Assert Acknowledge Flag
Clear in master and slave receiver modes, to force a not acknowledge (high level on SDA). Clear to disable SLA or GCA
recognition. Set to recognize SLA or GCA (if GC set) for entering slave receiver or transmitter modes. Set in master and
slave receiver modes, to force an acknowledge (low level on SDA). This bit has no effect when in master transmitter
mode. By clearing AA to zero, the device can be virtually disconnected from the Two-wire Serial Bus temporarily. Address
recognition can then be resumed by setting the AA bit to one again.
CR1
Bit Control Rate 1
Sets the bit rate for TWI master mode along with C0 and CR2. See Table 18-1.
CR0
Bit Control Rate 02
Sets the bit rate for TWI master mode along with C1 and CR2. See Table 18-1.
145
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 18-3.
SSCS – Two-Wire Status Register
SSCS Address = ABH
Reset Value = 1111 1000B
Not Bit Addressable
Bit
SC7
SC6
SC5
SC4
SC3
0
0
0
7
6
5
4
3
2
1
0
Symbol
Function
SC7-0
Two-wire Interface Status
The current status code of the TWI logic and serial bus. See Table 18-6 through Table 18-10 for a description of the
status codes. Note that the three least significant bits always read as zero. The Status code is valid only while SI remains
set.
Table 18-4.
SSADR – Two-Wire Address Register
SSADR Address = ACH
Reset Value = 1111 1110B
Not Bit Addressable
Bit
SA6
SA5
SA4
SA3
SA2
SA1
SA0
GC
7
6
5
4
3
2
1
0
Symbol
Function
SA6-0
Two-wire Interface Slave Address
The TWI will only respond to slave addresses that match this 7-bit address.
GC
General Call Enable
Set to enable General Call address (00h) recognition. Clear to disable General Call address recognition.
Table 18-5.
SSDAT – Two-Wire Data Register
SSDAT Address = ADH
Reset Value = 1111 1111B
Not Bit Addressable
Bit
SD7
SD6
SD5
SD4
SD3
SD2
SD1
SD0
7
6
5
4
3
2
1
0
Symbol
Function
SD7-0
Two-wire Interface Serial Data
Writes to SSDAT queue the next address or data byte for transmission. Reads from SSDAT return the last address or
data byte present on the bus. Writes/reads to/from SSDAT must occur only while SI is set. Writes to SSDAT while SI = 0
are ignored. Reads from SSDAT while SI = 0 may return random data.
18.5
Using the TWI
The AT89LP TWI is byte-oriented and interrupt based. Interrupts are issued after all bus events,
like reception of a byte or transmission of a START condition. Because the TWI is interruptbased, the application software is free to carry on other operations during a TWI byte transfer.
Note that the TWI Interrupt Enable (ETWI) bit in IE2 together with the Global Interrupt Enable bit
in EA allow the application to decide whether or not assertion of the SI flag should generate an
146
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
interrupt request. If the TWE bit is cleared, the application must poll the SI flag in order to detect
actions on the TWI bus.
When the SI flag is asserted, the TWI has finished an operation and awaits application
response. In this case, the TWI Status Register (SSCS) contains a value indicating the current
state of the TWI bus. The application software can then decide how the TWI should behave in
the next TWI bus cycle by manipulating the SSCON and SSDAT registers.
Figure 18-10 is a simple example of how the application can interface to the TWI hardware. In
this example, a Master wishes to transmit a single data byte to a Slave. This description is quite
abstract, a more detailed explanation follows later in this section. A simple code example implementing the desired behavior is also presented.
Application
Action
Figure 18-10. Interfacing the Application to the TWI in a Typical Transmission
1. Application writes
to SSCON to initiate
transmission of
START
TWI
Hardware
Action
TWI bus
3. Check SSCS to see if START was
sent. Application loads SLA+W into
SSDAT, and loads appropriate control
signals into SSCON, making sure that
SI is written to zero and
STA is written to zero.
START
2. SI set.
Status code indicates
START condition sent
SLA+W
5. Check SSCS to see if SLA+W was
sent and ACK received.
Application loads data into SSDAT,
and loads appropriate control signals
into SSCON, making sure that
SI is written to zero.
A
4. SI set.
Status code indicates
SLA+W sent, ACK
received
Data
7. Check SSCS to see if data was sent
and ACK received. Application loads
appropriate control signals to send
STOP into SSCON, making sure that
SI is written to zero.
A
6. SI set.
Status code indicates
data sent, ACK received
STOP
Indicates
SI set
1. The first step in a TWI transmission is to transmit a START condition. This is done by
writing a specific value into SSCON, instructing the TWI hardware to transmit a START
condition. Which value to write is described later on. However, it is important that the SI
bit is cleared in the value written. The TWI will not start any operation as long as the SI
bit in SSCON is set. Immediately after the application has cleared SI, the TWI will initiate transmission of the START condition.
2. When the START condition has been transmitted, the SI flag in SSCON is set, and
SSCS is updated with a status code indicating that the START condition has successfully been sent.
3. The application software should now examine the value of SSCS, to make sure that the
START condition was successfully transmitted. If SSCS indicates otherwise, the application software might take some special action, like calling an error routine. Assuming
that the status code is as expected, the application must load SLA+W into SSDAT.
Remember that SSDAT is used both for address and data. After SSDAT has been
loaded with the desired SLA+W, a specific value must be written to SSCON, instructing
the TWI hardware to transmit the SLA+W present in SSDAT. Which value to write is
described later on. However, it is important that the SI bit is cleared in the value written.
The TWI will not start any operation as long as the SI bit in SSCON is set. Immediately
after the application has cleared SI, the TWI will initiate transmission of the address
packet.
147
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
4. When the address packet has been transmitted, the SI flag in SSCON is set, and SSCS
is updated with a status code indicating that the address packet has successfully been
sent. The status code will also reflect whether a slave acknowledged the packet or not.
5. The application software should now examine the value of SSCS, to make sure that the
address packet was successfully transmitted, and that the value of the ACK bit was as
expected. If SSCS indicates otherwise, the application software might take some special action, like calling an error routine. Assuming that the status code is as expected,
the application must load a data packet into SSDAT. Subsequently, a specific value
must be written to SSCON, instructing the TWI hardware to transmit the data packet
present in SSDAT. Which value to write is described later on. However, it is important
that the SI bit is cleared in the value written. The TWI will not start any operation as long
as the SI bit in SSCON is set. Immediately after the application has cleared SI, the TWI
will initiate transmission of the data packet.
6. When the data packet has been transmitted, the SI flag in SSCON is set, and SSCS is
updated with a status code indicating that the data packet has successfully been sent.
The status code will also reflect whether a slave acknowledged the packet or not.
7. The application software should now examine the value of SSCS, to make sure that the
data packet was successfully transmitted, and that the value of the ACK bit was as
expected. If SSCS indicates otherwise, the application software might take some special action, like calling an error routine. Assuming that the status code is as expected,
the application must write a specific value to SSCON, instructing the TWI hardware to
transmit a STOP condition. Which value to write is described later on. However, it is
important that the SI bit is cleared in the value written. The TWI will not start any operation as long as the SI bit in SSCON is set. Immediately after the application has cleared
SI, the TWI will initiate transmission of the STOP condition. Note that SI is NOT set
after a STOP condition has been sent.
Even though this example is simple, it shows the principles involved in all TWI transmissions.
These can be summarized as follows:
• When the TWI has finished an operation and expects application response, the SI flag is set.
The SCL line is pulled low until SI is cleared.
• When the SI flag is set, the user must update all TWI registers with the value relevant for the
next TWI bus cycle. As an example, SSDAT must be loaded with the value to be transmitted
in the next bus cycle.
• After all TWI Register updates and other pending application software tasks have been
completed, SSCON is written. When writing SSCON, the SI bit should be cleared. The TWI
will then commence executing whatever operation was specified by the SSCON setting.
18.6
Transmission Modes
The TWI can operate in one of four major modes. These are named Master Transmitter (MT),
Master Receiver (MR), Slave Transmitter (ST) and Slave Receiver (SR). Several of these
modes can be used in the same application. As an example, the TWI can use MT mode to write
data into a TWI EEPROM, MR mode to read the data back from the EEPROM. If other masters
are present in the system, some of these might transmit data to the TWI, and then SR mode
would be used. It is the application software that decides which modes are legal.
The following sections describe each of these modes. Possible status codes are described
along with figures detailing data transmission in each of the modes. These figures contain the
following abbreviations:
148
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
S: START condition
Rs: REPEATED START condition
R: Read bit (high level at SDA)
W: Write bit (low level at SDA)
A: Acknowledge bit (low level at SDA)
A: Not acknowledge bit (high level at SDA)
Data: 8-bit data byte
P: STOP condition
SLA: Slave Address
In Figure 18-11 to Figure 18-14, circles are used to indicate that the SI flag is set. The numbers
in the circles show the status code held in SSCS. At these points, actions must be taken by the
application to continue or complete the TWI transfer. The TWI transfer is suspended until the SI
flag is cleared by software.
When the SI flag is set, the status code in SSCS is used to determine the appropriate software
action. For each status code, the required software action and details of the following serial
transfer are given in Table 18-6 to Table 18-9.
18.6.1
Master Transmitter Mode
In the Master Transmitter mode, a number of data bytes are transmitted to a Slave Receiver. In
order to enter a Master mode, a START condition must be transmitted. The format of the following address packet determines whether Master Transmitter or Master Receiver mode is to be
entered. If SLA+W is transmitted, MT mode is entered, if SLA+R is transmitted, MR mode is
entered.
A START condition is sent by writing the following value to SSCON:
SSCON
Value
CR2
SSIE
STA
STO
SI
AA
CR1
CR0
bit rate
1
1
0
0
X
bit rate
bit rate
SSIE must be set to enable the Two-wire Serial Interface, STA must be written to one to transmit
a START condition and SI must be cleared. The TWI will then test the Two-wire Serial Bus and
generate a START condition as soon as the bus becomes free. After a START condition has
been transmitted, the SI flag is set by hardware, and the status code in SSCS will be 08h (see
Table 18-6). In order to enter MT mode, SLA+W must be transmitted. This is done by writing
SLA+W to SSDAT. Thereafter the SI bit should be cleared to continue the transfer.
When SLA+W has been transmitted and an acknowledgment bit has been received, SI is set
again and a number of status codes in SSCS are possible. Possible status codes in Master
mode are 18h, 20h, or 38h. The appropriate action to be taken for each of these status codes is
detailed in Table 18-6.
After SLA+W has been successfully transmitted, a data packet should be transmitted. This is
done by writing the data byte to SSDAT. SSDAT must only be written when SI is high. If not, the
access will be discarded and the previous value will be transmitted. After updating SSDAT, the
SI bit should be cleared to continue the transfer. This scheme is repeated until the last byte has
been sent and the transfer is ended by generating a STOP condition or a repeated START condition. A STOP condition is generated by writing the following value to SSCON:
149
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
SSCON
Value
CR2
SSIE
STA
STO
SI
AA
CR1
CR0
bit rate
1
0
1
0
X
bit rate
bit rate
A REPEATED START condition is generated by writing the following value to SSCON:
SSCON
Value
CR2
SSIE
STA
STO
SI
AA
CR1
CR0
bit rate
1
1
0
0
X
bit rate
bit rate
After a repeated START condition (status 10h) the Two-wire Serial Interface can access the
same slave again, or a new slave without transmitting a STOP condition. Repeated START
enables the master to switch between slaves, Master Transmitter mode and Master Receiver
mode without losing control of the bus.
.
Table 18-6.
Status Codes for Master Transmitter Mode
Application Software Response
Status
Code
(SSCS)
Status of the Two-wire
Serial Bus and Two-wire
Serial Interface Hardware
0x08
A START condition has
been transmitted
10h
A repeated START
condition has been
transmitted
18h
20h
28h
150
SLA+W has been
transmitted; ACK has been
received
SLA+W has been
transmitted; NOT ACK has
been received
Data byte has been
transmitted; ACK has been
received
To SSCON
To/from SSDAT
STA
STO
SI
AA
Next Action Taken by TWI Hardware
Load SLA+W
0
0
1
X
SLA+W will be transmitted;
ACK or NOT ACK will be received
Load SLA+W
0
0
1
X
SLA+W will be transmitted;
ACK or NOT ACK will be received
Load SLA+R
0
0
1
X
SLA+R will be transmitted;
Logic will switch to Master Receiver mode
Load data byte
0
0
1
X
Data byte will be transmitted and ACK or NOT
ACK will be received
No action
1
0
1
X
Repeated START will be transmitted
No action
0
1
1
X
STOP condition will be transmitted and STO
flag will be reset
No action
1
1
1
X
STOP condition followed by a START condition
will be transmitted and STO flag will be reset
Load data byte
0
0
1
X
Data byte will be transmitted and ACK or NOT
ACK will be received
No action
1
0
1
X
Repeated START will be transmitted
No action
0
1
1
X
STOP condition will be transmitted and STO
flag will be reset
No action
1
1
1
X
STOP condition followed by a START condition
will be transmitted and STO flag will be reset
Load data byte
0
0
1
X
Data byte will be transmitted and ACK or NOT
ACK will be received
No action
1
0
1
X
Repeated START will be transmitted
No action
0
1
1
X
STOP condition will be transmitted and STO
flag will be reset
No action
1
1
1
X
STOP condition followed by a START condition
will be transmitted and STO flag will be reset
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 18-6.
30h
38h
18.6.2
Status Codes for Master Transmitter Mode
Data byte has been
transmitted; NOT ACK has
been received
Load data byte
0
0
1
X
Data byte will be transmitted and ACK or NOT
ACK will be received
No action
1
0
1
X
Repeated START will be transmitted
No action
0
1
1
X
STOP condition will be transmitted and STO
flag will be reset
No action
1
1
1
X
STOP condition followed by a START condition
will be transmitted and STO flag will be reset
No action
0
0
1
X
Two-wire Serial Bus will be released and not
addressed slave mode entered
No action
1
0
1
X
A START condition will be transmitted when the
bus becomes free
Arbitration lost in SLA+W
or data bytes
Master Receiver Mode
In the Master Receiver mode, a number of data bytes are received from a slave transmitter. In
order to enter a Master mode, a START condition must be transmitted. The format of the following address packet determines whether Master Transmitter or Master Receiver mode is to be
entered. If SLA+W is transmitted, MT mode is entered, if SLA+R is transmitted, MR mode is
entered.
SSIE must be written to one to enable the Two-wire Serial Interface, STA must be written to one
to transmit a START condition and SI must be cleared. The TWI will then test the Two-wire
Serial Bus and generate a START condition as soon as the bus becomes free. After a START
condition has been transmitted, the SI flag is set by hardware, and the status code in SSCS will
be 08h (see Table 18-7). In order to enter MR mode, SLA+R must be transmitted. This is done
by writing SLA+R to SSDAT. Thereafter the SI bit should be cleared to continue the transfer.
When SLA+R has been transmitted and an acknowledgment bit has been received, SI is set
again and a number of status codes in SSCS are possible. Possible status codes in Master
mode are 38h, 40h or 48h. The appropriate action to be taken for each of these status codes is
detailed in Table 18-7. Received data can be read from the SSDAT Register when the SI flag is
set high by hardware. This scheme is repeated until the last byte has been received. After the
last byte has been received, the MR should inform the ST by sending a NACK after the last
received data byte. The transfer is ended by generating a STOP condition or a repeated START
condition.
151
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 18-11. Format and States in Master Transmitter Mode
MT
Successfull
transmission
to a slave
receiver
S
SLA
08h
W
A
DATA
18h
A
P
28h
Next transfer
started with a
repeated start
condition
RS
SLA
W
10h
Not acknowledge
received after the
slave address
A
R
P
20h
MR
Not acknowledge
received after a data
byte
A
P
30h
Arbitration lost in slave
address or data byte
A or A
Other master
continues
38h
Arbitration lost and
addressed as slave
A
68h
From master to slave
152
Other master
continues
38h
Other master
continues
78h
DATA
From slave to master
A or A
To corresponding
states in slave mode
B0h
A
n
Any number of data bytes
and their associated acknowledge bits
This number (contained in TWSR) corresponds
to a defined state of the Two-wire Serial Bus. The
prescaler bits are zero or masked to zero
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 18-7.
Status Codes for Master Receiver Mode
Application Software Response
Status
Code
(SSCS)
Status of the Two-wire
Serial Bus and Two-wire
Serial Interface Hardware
08h
A START condition has
been transmitted
10h
A repeated START
condition has been
transmitted
38h
40h
48h
50h
58h
To SSCON
To/from SSDAT
STA
STO
SI
AA
Load SLA+R
0
0
1
X
SLA+R will be transmitted; ACK or NOT ACK
will be received
Load SLA+R
0
0
1
X
SLA+R will be transmitted; ACK or NOT ACK
will be received
Load SLA+W
0
0
1
X
SLA+W will be transmitted; Logic will switch to
Master Transmitter mode
No action
0
0
1
X
Two-wire Serial Bus will be released and not
addressed Slave mode will be entered
No action
1
0
1
X
A START condition will be transmitted when the
bus becomes free
No action
0
0
1
0
Data byte will be received and NOT ACK will be
returned
No action
0
0
1
1
Data byte will be received and ACK will be
returned
No action
1
0
1
X
Repeated START will be transmitted
No action
0
1
1
X
STOP condition will be transmitted and STO
flag will be reset
No action
1
1
1
X
STOP condition followed by a START condition
will be transmitted and STO flag will be reset
Read data byte
0
0
1
0
Data byte will be received and NOT ACK will be
returned
Read data byte
0
0
1
1
Data byte will be received and ACK will be
returned
Read data byte
1
0
1
X
Repeated START will be transmitted
Read data byte
0
1
1
X
STOP condition will be transmitted and STO
flag will be reset
Read data byte
1
1
1
X
STOP condition followed by a START condition
will be transmitted and STO flag will be reset
Arbitration lost in SLA+R or
NOT ACK bit
SLA+R has been
transmitted; ACK has been
received
SLA+R has been
transmitted; NOT ACK has
been received
Data byte has been
received; ACK has been
returned
Data byte has been
received; NOT ACK has
been returned
Next Action Taken by TWI Hardware
153
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 18-12. Format and States in Master Receiver Mode
MR
Successfull
reception
from a slave
receiver
S
SLA
R
A
DATA
A
40h
08h
DATA
50h
A
P
58h
Next transfer
started with a
repeated start
condition
RS
SLA
R
10h
Not acknowledge
received after the
slave address
A
W
P
48h
MT
Arbitration lost in slave
address or data byte
A or A
Other master
continues
A
38h
Arbitration lost and
addressed as slave
A
68h
From master to slave
18.6.3
38h
Other master
continues
78h
To corresponding
states in slave mode
B0h
DATA
From slave to master
Other master
continues
Any number of data bytes
and their associated acknowledge bits
A
This number (contained in TWSR) corresponds
to a defined state of the Two-wire Serial Bus. The
prescaler bits are zero or masked to zero
n
Slave Receiver Mode
In the Slave Receiver mode, a number of data bytes are received from a master transmitter. To
initiate the Slave Receiver mode, SSADR and SSCON must be initialized as follows:
SSADR
S6
SA5
Value
SA4
SA3
SA2
SA1
SA0
Device’s own Slave Address
GC
X
The upper seven bits are the address to which the Two-wire Serial Interface will respond when
addressed by a master. If the LSB is set, the TWI will respond to the general call address (00h),
otherwise it will ignore the general call address.:
SSCON
Value
154
CR2
SSIE
STA
STO
SI
AA
CR1
CR0
X
1
0
0
0
1
X
X
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
SSIE must be written to one to enable the TWI. The AA bit must be written to one to enable the
acknowledgment of the device’s own slave address or the general call address. STA and STO
must be written to zero.
When SSADR and SSCON have been initialized, the TWI waits until it is addressed by its own
slave address (or the general call address if enabled) followed by the data direction bit. If the
direction bit is “0” (write), the TWI will operate in SR mode, otherwise ST mode is entered. After
its own slave address and the write bit have been received, the SI flag is set and a valid status
code can be read from SSCS. The status code is used to determine the appropriate software
action. The appropriate action to be taken for each status code is detailed in Table 18-8. The
Slave Receiver mode may also be entered if arbitration is lost while the TWI is in the Master
mode (see states 68h and 78h).
If the AA bit is reset during a transfer, the TWI will return a “Not Acknowledge” (“1”) to SDA after
the next received data byte. This can be used to indicate that the slave is not able to receive any
more bytes. While AA is zero, the TWI does not acknowledge its own slave address. However,
the Two-wire Serial Bus is still monitored and address recognition may resume at any time by
setting AA. This implies that the AA bit may be used to temporarily isolate the TWI from the Twowire Serial Bus.
.
Table 18-8.
Status Codes for Slave Receiver Mode
Application Software Response
Status
Code
(SSCS)
Status of the Two-wire
Serial Bus and Two-wire
Serial Interface Hardware
60h
Own SLA+W has been
received; ACK has been
returned
Arbitration lost in SLA+R/W
as master; own SLA+W has
been received; ACK has
been returned
68h
70h
78h
80h
To SSCON
To/from SSDAT
STA
STO
SI
AA
Next Action Taken by TWI Hardware
No action
X
0
1
0
Data byte will be received and NOT ACK will be
returned
No action
X
0
1
1
Data byte will be received and ACK will be
returned
No action
X
0
1
0
Data byte will be received and NOT ACK will be
returned
No action
X
0
1
1
Data byte will be received and ACK will be
returned
General call address has
been received; ACK has
been returned
No action
X
0
1
0
Data byte will be received and NOT ACK will be
returned
No action
X
0
1
1
Data byte will be received and ACK will be
returned
Arbitration lost in SLA+R/W
as master; General call
address has been received;
ACK has been returned
No action
X
0
1
0
Data byte will be received and NOT ACK will be
returned
No action
X
0
1
1
Data byte will be received and ACK will be
returned
Previously addressed with
own SLA+W; data has been
received; ACK has been
returned
Read data byte
X
0
1
0
Data byte will be received and NOT ACK will be
returned
Read data byte
X
0
1
1
Data byte will be received and ACK will be
returned
155
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 18-8.
88h
90h
98h
A0h
Status Codes for Slave Receiver Mode
Previously addressed with
own SLA+W; data has been
received; NOT ACK has
been returned
Previously addressed with
general call; data has been
received; ACK has been
returned
Previously addressed with
general call; data has been
received; NOT ACK has
been returned
A STOP condition or
repeated START condition
has been received while still
addressed as slave
Read data byte
0
0
1
0
Switched to the not addressed Slave mode; no
recognition of own SLA or GCA
Read data byte
0
0
1
1
Switched to the not addressed Slave mode;
own SLA will be recognized; GCA will be
recognized if GC = “1”
0
Switched to the not addressed Slave mode; no
recognition of own SLA or GCA; a START
condition will be transmitted when the bus
becomes free
Read data byte
0
1
Read data byte
1
0
1
1
Switched to the not addressed Slave mode;
own SLA will be recognized; GCA will be
recognized if GC = “1”; a START condition will
be transmitted when the bus becomes free
Read data byte
X
0
1
0
Data byte will be received and NOT ACK will be
returned
Read data byte
X
0
1
1
Data byte will be received and ACK will be
returned
Read data byte
0
0
1
0
Switched to the not addressed Slave mode; no
recognition of own SLA or GCA
Read data byte
0
0
1
1
Switched to the not addressed Slave mode;
own SLA will be recognized; GCA will be
recognized if GC = “1”
0
Switched to the not addressed Slave mode; no
recognition of own SLA or GCA; a START
condition will be transmitted when the bus
becomes free
Read data byte
1
0
1
Read data byte
1
0
1
1
Switched to the not addressed Slave mode;
own SLA will be recognized; GCA will be
recognized if GC = “1”; a START condition will
be transmitted when the bus becomes free
No Action
0
0
1
0
Switched to the not addressed Slave mode; no
recognition of own SLA or GCA
No Action
0
0
1
1
Switched to the not addressed Slave mode;
own SLA will be recognized; GCA will be
recognized if GC = “1”
0
Switched to the not addressed Slave mode; no
recognition of own SLA or GCA; a START
condition will be transmitted when the bus
becomes free
1
Switched to the not addressed Slave mode;
own SLA will be recognized; GCA will be
recognized if GC = “1”; a START condition will
be transmitted when the bus becomes free
No Action
No Action
156
1
1
1
0
0
1
1
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 18-13. Format and States in Slave Receiver Mode
Reception of the own
slave address and one or
more data bytes. All are
acknowledged
S
SLA
W
A
DATA
60h
A
DATA
80h
Last data byte received
is not acknowledged
A
P or S
80h
A0h
A
P or S
88h
Arbitration lost as master
and addressed as slave
A
68h
Reception of the general call
address and one or more data
bytes
General Call
A
DATA
70h
A
DATA
90h
Last data byte received is
not acknowledged
A
P or S
90h
A0h
A
P or S
98h
Arbitration lost as master and
addressed as slave by general call
A
78h
From master to slave
DATA
From slave to master
A
n
Any number of data bytes
and their associated acknowledge bits
This number (contained in TWSR) corresponds
to a defined state of the Two-wire Serial Bus. The
prescaler bits are zero or masked to zero
157
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
18.6.4
Slave Transmitter Mode
In the Slave Transmitter mode, a number of data bytes are transmitted to a master receiver. To
initiate the Slave Transmitter mode, upper 7 bits of SSADR must be initialized with the address
to which the Two-wire Serial Interface will respond when addressed by a master. If the LSB is
set, the TWI will respond to the general call address (00h), otherwise it will ignore the general
call address. SSIE must be written to one to enable the TWI. The AA bit must be written to one
to enable the acknowledgment of the device’s own slave address or the general call address.
STA and STO must be written to zero.
When SSADR and SSCON have been initialized, the TWI waits until it is addressed by its own
slave address (or the general call address if enabled) followed by the data direction bit. If the
direction bit is “1” (read), the TWI will operate in ST mode, otherwise SR mode is entered. After
its own slave address and the write bit have been received, the TWINT flag is set and a valid
status code can be read from SSCS. The status code is used to determine the appropriate software action. The appropriate action to be taken for each status code is detailed in Table 18-9.
The Slave Transmitter mode may also be entered if arbitration is lost while the TWI is in the
Master mode (see state B0h).
If the AA bit is written to zero during a transfer, the TWI will transmit the last byte of the transfer.
State C0h or state C8h will be entered, depending on whether the master receiver transmits a
NACK or ACK after the final byte. The TWI is switched to the not addressed Slave mode, and
will ignore the master if it continues the transfer. Thus the master receiver receives all “1s” as
serial data. State C8h is entered if the master demands additional data bytes (by transmitting
ACK), even though the slave has transmitted the last byte (AA zero and expecting NACK from
the master). While AA is zero, the TWI does not respond to its own slave address. However, the
Two-wire Serial Bus is still monitored and address recognition may resume at any time by setting AA. This implies that the AA bit may be used to temporarily isolate the TWI from the Twowire Serial Bus.
Figure 18-14. Format and States in Slave Transmitter Mode
Reception of the own
slave address and one or
more data bytes
S
SLA
R
A
DATA
A8h
Arbitration lost as master
and addressed as slave
A
DATA
B8h
A
P or S
C0h
A
B0h
Last data byte transmitted.
Switched to not addressed
slave (TWEA = '0')
A
All 1's
P or S
C8h
From master to slave
DATA
From slave to master
158
A
n
Any number of data bytes
and their associated acknowledge bits
This number (contained in TWSR) corresponds
to a defined state of the Two-wire Serial Bus. The
prescaler bits are zero or masked to zero
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
.
Table 18-9.
Status Codes for Slave Transmitter Mode
Application Software Response
Status
Code
(SSCS)
Status of the Two-wire
Serial Bus and Two-wire
Serial Interface Hardware
A8h
Own SLA+R has been
received; ACK has been
returned
B0h
B8h
C0h
C8h
Arbitration lost in SLA+R/W
as master; own SLA+R has
been received; ACK has
been returned
Data byte in SSDAT has
been transmitted; ACK has
been received
Data byte in SSDAT has
been transmitted; NOT ACK
has been received
Last data byte in SSDAT has
been transmitted (AA = “0”);
ACK has been received
To SSCON
To/from SSDAT
STA
STO
SI
AA
Load data byte
X
0
1
0
Last data byte will be transmitted and NOT
ACK should be received
Load data byte
X
0
1
1
Data byte will be transmitted and ACK should
be received
Load data byte
X
0
1
0
Last data byte will be transmitted and NOT
ACK should be received
Load data byte
X
0
1
1
Data byte will be transmitted and ACK should
be received
Load data byte
X
0
1
0
Last data byte will be transmitted and NOT
ACK should be received
Load data byte
X
0
1
1
Data byte will be transmitted and ACK should
be received
No action
0
0
1
0
Switched to the not addressed Slave mode; no
recognition of own SLA or GCA
No action
0
0
1
1
Switched to the not addressed Slave mode;
own SLA will be recognized; GCA will be
recognized if GC = “1”
0
Switched to the not addressed Slave mode; no
recognition of own SLA or GCA; a START
condition will be transmitted when the bus
becomes free
No action
0
1
No action
1
0
1
1
Switched to the not addressed Slave mode;
own SLA will be recognized; GCA will be
recognized if GC = “1”; a START condition will
be transmitted when the bus becomes free
No action
0
0
1
0
Switched to the not addressed Slave mode; no
recognition of own SLA or GCA
No action
0
0
1
1
Switched to the not addressed Slave mode;
own SLA will be recognized; GCA will be
recognized if GC = “1”
0
Switched to the not addressed Slave mode; no
recognition of own SLA or GCA; a START
condition will be transmitted when the bus
becomes free
1
Switched to the not addressed Slave mode;
own SLA will be recognized; GCA will be
recognized if GC = “1”; a START condition will
be transmitted when the bus becomes free
No action
No action
18.6.5
1
Next Action Taken by TWI Hardware
1
1
0
0
1
1
Miscellaneous States
There are two status codes that do not correspond to a defined TWI state, see Table 18-10.
Status F8h indicates that no relevant information is available because the SI flag is not set. This
occurs between other states, and when the TWI is not involved in a serial transfer.
Status 00h indicates that a bus error has occurred during a Two-wire Serial Bus transfer. A bus
error occurs when a START or STOP condition occurs at an illegal position in the format frame.
159
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Examples of such illegal positions are during the serial transfer of an address byte, a data byte,
or an acknowledge bit. When a bus error occurs, SI is set. To recover from a bus error, the STO
flag must set and SI must be cleared. This causes the TWI to enter the not addressed Slave
mode and to clear the STO flag (no other bits in SSCON are affected). The SDA and SCL lines
are released, and no STOP condition is transmitted.
Table 18-10. Miscellaneous States
Application Software Response
Status
Code
(SSCS)
Status of the Two-wire
Serial Bus and Two-wire
Serial Interface hardware
F8h
No relevant state
information available; SI =
“0”
No action
00h
Bus error due to an illegal
START or STOP condition
No action
18.6.6
To SSCON
To/from SSDAT
STA
STO
SI
AA
No action
0
1
Next Action Taken by TWI Hardware
Wait or proceed current transfer
1
X
Only the internal hardware is affected, no STOP
condition is sent on the bus. In all cases, the
bus is released and STO is cleared.
Combining Several TWI Modes
In some cases, several TWI modes must be combined in order to complete the desired action.
Consider for example reading data from a serial EEPROM. Typically, such a transfer involves
the following steps:
1. The transfer must be initiated.
2. The EEPROM must be instructed what location should be read.
3. The reading must be performed.
4. The transfer must be finished.
Note that data is transmitted both from Master to Slave and vice versa. The Master must instruct
the Slave what location it wants to read, requiring the use of the MT mode. Subsequently, data
must be read from the Slave, implying the use of the MR mode. Thus, the transfer direction must
be changed. The Master must keep control of the bus during all these steps, and the steps
should be carried out as an atomic operation. If this principle is violated in a multi-master system, another Master can alter the data pointer in the EEPROM between steps 2 and 3, and the
Master will read the wrong data location. Such a change in transfer direction is accomplished by
transmitting a REPEATED START between the transmission of the address byte and reception
of the data. After a REPEATED START, the Master keeps ownership of the bus. The following
figure shows the flow in this transfer.
Figure 18-15. Combining Several TWI Modes to Access a Serial EEPROM
Master Transmitter
S
SLA+W
A
ADDRESS
S = START
Transmitted from master to slave
160
Master Receiver
A
Rs
SLA+R
A
Rs = REPEATED START
DATA
A
P
P = STOP
Transmitted from slave to master
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
19. Dual Analog Comparators
The AT89LP51RD2/ED2/ID2 provides two analog comparators. The analog comparators have
the following features:
• Internal 3-level Voltage Reference (1.125V, 1.25V, 1.375V)
• Four Shared Analog Input Channels
– Configure as Multiple Input Window Comparator
• Selectable Interrupt Conditions
– High- or Low-level
– Rising- or Falling-edge
– Output Toggle
• Hardware Debouncing Modes
Figure 19-1. Dual Comparator Block Diagram
11
(P2.7) AIN3
10
01
00
B
11
CSB1
CSB0
(P2.6) AIN2
10
01
00
CMB2
CMB1
CSA0
CSA1
(P2.4) AIN0
Interrupt
CMA2
CMA1
00
01
10
11
00
01
10
CFB
CMB0
RFB0
RFB1
RFA1
RFA0
(P2.5) AIN1
CMPB
CFA
ECMP
CMA0
A
CMPA
11
VAREF+Δ
VAREF
VAREF-Δ
A block diagram of the dual analog comparators with relevant connections is shown in Figure
19-1. Input options allow the comparators to function in a number of different configurations as
shown in Figure 19-4. Comparator operation is such that the output is a logic “1” when the positive input is greater than the negative input. Otherwise the output is a zero. Setting the CENA
(ACSRA.3) and CENB (ACSRB.3) bits enable Comparator A and B respectively. The user must
also set the CONA (ACSRA.5) or CONB (ACSRB.5) bits to connect the comparator inputs
before using a comparator. When a comparator is first enabled, the comparator output and interrupt flag are not guaranteed to be stable for 10 µs. The corresponding comparator interrupt
should not be enabled during that time, and the comparator interrupt flag must be cleared before
the interrupt is enabled in order to prevent an immediate interrupt service.
Before enabling the comparators, the analog inputs should be tristated by putting P2.4, P2.5,
P2.6 and P2.7 into input-only mode. See “Port Analog Functions” on page 76. It is not possible
to use the Analog Comparators with external program memory or external data memory with 16bit addresses (MOVX @DPTR) since these functions require the use of Port 2 for addressing.
161
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Each comparator may be configured to cause an interrupt under a variety of output value conditions by setting the CMx2-0 bits in ACSRx (See Table 19-1 or Table 19-2). The comparator
interrupt flags CFx in ACSRx are set whenever the comparator outputs match the conditions
specified by CMx2-0. The flags may be polled by software or may be used to generate an interrupt and must be cleared by software. Both comparators share a common interrupt vector. If
both comparators are enabled, the user needs to read the flags after entering the interrupt service routine to determine which comparator caused the interrupt.
The CCS1-0 bits in AREF (Table 19-3) control when the comparator interrupts sample the comparator outputs. Normally the outputs are sampled every clock system; however, the outputs
may also be sampled whenever Timer 0, Timer 1 or Timer 2 overflows. These settings allow the
comparators to be sampled at a specific time or to reduce the number of comparator events
seen by the system when using level sensitive modes. The raw value of the comparator outputs
can always be read from the CMPA and CMPB bits in AREF.
The comparators will continue to function during Idle mode. If this is not the desired behavior,
the comparators should be disabled before entering Idle. The comparators are always disabled
during Power-down mode.
19.1
Analog Input Muxes
The positive input terminal of each comparator may be connected to any of the four analog input
pins by changing the CSA1-0 or CSB1-0 bits in ACSRA and ACSRB. When changing the analog
input pins, the comparator must be disconnected from its inputs by clearing the CONA or CONB
bits. The connection is restored by setting the bits again after the muxes have been modified.
CLR
EC
ANL
...
ORL
ACSRA, #0DFh ; Clear CONA to disconnect COMP A
; Modify CSA or RFA bits
ACSRA, #020h ; Set CONA to connect COMP A
ANL
ACSRA, #0EFh ; Clear any spurious interrupt
SETB
; Disable comparator interrupts
EC
; Re-enable comparator interrupts
The corresponding comparator interrupt should not be enabled while the inputs are being
changed, and the comparator interrupt flag must be cleared before the interrupt is re-enabled in
order to prevent an unintentional interrupt request.
The equivalent model for the analog input circuitry is illustrated in Figure 20-2. An analog source
applied to AINn is subjected to the pin capacitance and input leakage of that pin, regardless of
whether that channel is selected as input to the comparator. When the channel is selected, the
source must drive the input capacitance of the comparator through the series resistance (combined resistance in the input path).
Figure 19-2. Equivalent Analog Input Model
RIN =
10 kΩ
RMUX =
10 kΩ
AINn
CPIN =
10 pF
162
CCMP <
0.3 pF
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
19.2
Internal Reference Voltage
The negative input terminal of each comparator may be connected to an internal voltage reference by changing the RFB1-0 or RFA1-0 bits in AREF. The internal reference voltage, VAREF, is
set to 1.25 V ±5%. The voltage reference also provides two additional voltage levels approximately 125 mV above and below VAREF. These levels may be used to configure the comparators
as an internally referenced window comparator with up to four input channels. Changing the reference input must follow the same routine used for changing the positive input as described in
“Analog Input Muxes” above.
19.3
Comparator Interrupt Debouncing
The comparator output is normally sampled every clock cycle. The conditions on the analog
inputs may be such that the comparator output will toggle excessively. This is especially true if
applying slow moving analog inputs. Three debouncing modes are provided to filter out this
noise for edge-triggered interrupts. In debouncing mode, the comparator uses Timer 1 to modulate its sampling time when CxC1-0 = 00B. When a relevant transition occurs, the comparator
waits until two Timer 1 overflows have occurred before resampling the output. If the new sample
agrees with the expected value, CFx is set. Otherwise, the event is ignored. The filter may be
tuned by adjusting the time-out period of Timer 1. Because Timer 1 is free running, the
debouncer must wait for two overflows to guarantee that the sampling delay is at least 1 time-out
period. Therefore, after the initial edge event, the interrupt may occur between 1 and 2 time-out
periods later. See Figure 19-3. When the comparator clock is provided by one of the timer overflows, i.e. CxC1-0 != 00B, any change in the comparator output must be valid after 4 samples to
be accepted as an edge event.
Figure 19-3. Negative Edge with Debouncing Example
Comparator Out
Timer 1 Overflow
CFx
Start
Compare
(rejected)
Start
Compare
(accepted)
When the comparator sampling clock is configured for a timer overflow, Timer 1 still controls the
debouncing. The sampling clock will determine when the edge event occurs and the interrupt will
be validated two Timer 1 overflows after this event. When Timer 1 is selected for the sampling
clock, this means the interrupt will occur on the second overflow after the overflow that sampled
desired event.
163
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 19-4. Dual Comparator Configuration Examples
a. dual independent comparators with external references
+
AIN0
-
AIN1
A
AIN3
+
AIN2
-
CMPA
B
f. 2-channel window
comparator with
external reference
CMPB
-
AIN2
CSA = 00 RFA = 00
CSB = 11 RFB = 00
+
B
CMPB
A
CMPA
AIN0
b. 3-channel comparator with external reference
AIN3
AIN0
+
AIN2
AIN1
AIN3
-
+
A
CMPA
-
AIN1
CSA = 00/10/11 RFA = 00
CSA = CSB = 00/11
RFA = RFB = 00
c. 4-channel comparator with internal reference
AIN0
+
AIN1
VAREF
AIN2
AIN3
-
A
CMPA
g. 4-channel window
comparator with
internal reference
CSA = 00/01/10/11 RFA = 10
d. 2-channel comparator with internal reference &
comparator with external reference
AIN0
+
AIN1
VAREF
-
A
CMPA
AIN3
AIN2
CSA = 00/01 RFA = 10
VAREF+Δ
AIN0
+
-
B
CMPB
+
+
AIN1
-
A
CMPA
CSB = 11 RFB = 00
AIN3
VAREF
CSA = 00/10 RFA = 00
164
CMPB
A
CMPA
AIN2
e. 2-channel comparator with external reference &
comparator with internal reference
AIN0
B
AIN1
+
AIN3
VAREF-Δ
AIN2
-
-
CSA = CSB = 00/01/10/11
RFA = 01 RFB = 11
+
-
B
CMPB
CSB = 11 RFB = 10
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 19-1.
ACSRA – Analog Comparator A Control & Status Register
ACSRA = A3H
Reset Value = 0000 0000B
Not Bit Addressable
CSA1
CSA0
CONA
CFA
CENA
CMA2
CMA1
CMA0
7
6
5
4
3
2
1
0
Bit
Symbol
Function
CSA1-0
Comparator A Positive Input Channel Select(1)
CSA1
CSA0
A+ Channel
0
0
AIN0 (P2.4)
0
1
AIN1 (P2.5)
1
0
AIN2 (P2.6)
1
1
AIN3 (P2.7)
CONA
Comparator A Input Connect
When CONA = 1 the analog input pins are connected to the comparator. When CONA = 0 the analog input pins are
disconnected from the comparator. CONA must be cleared to 0 before changing CSA[1-0] or RFA[1-0].
CFA
Comparator A Interrupt Flag
Set when the comparator output meets the conditions specified by the CMA [2-0] bits and CENA is set. The flag must be
cleared by software. The interrupt may be enabled/disabled by setting/clearing bit 6 of IE.
CENA
Comparator A Enable
Set this bit to enable the comparator. Clearing this bit will force the comparator output low and prevent further events
from setting CFA. When CENA = 1 the analog input pins, P2.4—P2.7, have their digital inputs disabled if they are
configured in input-only mode.
CMA2-0
Comparator A Interrupt Mode
Notes:
CMA2
CMA1
CMA0
Interrupt Mode
0
0
0
Negative (Low) level
0
0
1
Positive edge
0
1
0
Toggle with debouncing(2)
0
1
1
Positive edge with debouncing(2)
1
0
0
Negative edge
1
0
1
Toggle
1
1
0
Negative edge with debouncing(2)
1
1
1
Positive (High) level
1. CONA must be cleared to 0 before changing CSA1-0.
2. Debouncing modes require the use of Timer 1 to generate the sampling delay.
165
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 19-2.
ACSRB – Analog Comparator B Control & Status Register
ACSRB = ABH
Reset Value = 1100 0000B
Not Bit Addressable
CSB1
CSB0
CONB
CFB
CENB
CMB2
CMB1
CMB0
7
6
5
4
3
2
1
0
Bit
Symbol
Function
CSB1-0
Comparator B Positive Input Channel Select(1)
CSB1
CSB0
B+ Channel
0
0
AIN0 (P2.4)
0
1
AIN1 (P2.5)
1
0
AIN2 (P2.6)
1
1
AIN3 (P2.7)
CONB
Comparator B Input Connect
When CONB = 1 the analog input pins are connected to the comparator. When CONB = 0 the analog input pins are
disconnected from the comparator. CONB must be cleared to 0 before changing CSB[1-0] or RFB[1-0].
CFB
Comparator B Interrupt Flag
Set when the comparator output meets the conditions specified by the CMB [2-0] bits and CENB is set. The flag must be
cleared by software. The interrupt may be enabled/disabled by setting/clearing bit 6 of IE.
CENB
Comparator B Enable
Set this bit to enable the comparator. Clearing this bit will force the comparator output low and prevent further events
from setting CFB. When CENB = 1 the analog input pins, P2.4—P2.7, have their digital inputs disabled if they are
configured in input-only mode.
CMB2-0
Comparator B Interrupt Mode
Notes:
CMB2
CMB1
CMB0
Interrupt Mode
0
0
0
Negative (Low) level
0
0
1
Positive edge
0
1
0
Toggle with debouncing(2)
0
1
1
Positive edge with debouncing(2)
1
0
0
Negative edge
1
0
1
Toggle
1
1
0
Negative edge with debouncing(2)
1
1
1
Positive (High) level
1. CONB must be cleared to 0 before changing CSB1-0.
2. Debouncing modes require the use of Timer 1 to generate the sampling delay.
166
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 19-3.
AREF – Analog Comparator Reference Control Register
AREF = BDH
Reset Value = 0000 0000B
Not Bit Addressable
Bit
CMPB
CMPA
RFB1
RFB0
CCS1
CCS0
RFA1
RFA0
7
6
5
4
3
2
1
0
Symbol
Function
CMPB
Comparator B Output.
Copy of Comparator B raw output value sampled by the system clock.
CMPA
Comparator A Output
Copy of Comparator A raw output value sampled by the system clock.
RFB1-0
Comparator B Negative Input Channel Select(1)
CCS1-0
RFA1-0
Notes:
RFB1
RFB0
B- Channel
0
0
AIN2 (P2.6)
0
1
Internal VAREF- (~1.125V)
1
0
Internal VAREF (~1.25V)
1
1
Internal VAREF+ (~1.375V)
Comparator Clock Select
CCS1
CCS0
Clock Source
0
0
System Clock
0
1
Timer 0 Overflow
1
0
Timer 1 Overflow
1
1
Timer 2 Overflow
Comparator A Negative Input Channel Select(2)
RFA1
RFA0
A- Channel
0
0
AIN1 (P2.5)
0
1
Internal VAREF- (~1.125V)
1
0
Internal VAREF (~1.25V)
1
1
Internal VAREF+ (~1.375V)
1. CONB (ACSRB.5) must be cleared to 0 before changing RFB[1-0].
2. CONA (ACSRA.5) must be cleared to 0 before changing RFA[1-0].
167
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
20. Digital-to-Analog/Analog-to-Digital Converter
The AT89LP51RD2/ED2/ID2 includes a 10-bit Data Converter (DADC) with the following
features:
• Digital-to-Analog (DAC) or Analog-to-Digital (ADC) Mode
• 10-bit Resolution
• 6.5 µs Conversion Time
• 7 Multiplexed Single-ended Channels or 3 Differential Channels
• Internal Temperature Sensor or Supply Voltage Channels
• Selectable 1.0V±10% Internal Reference Voltage
• Optional Left-Adjust of Conversion Results
• Single Conversion or Timer-triggered Mode
• Interrupt on Conversion Complete
The AT89LP51RD2/ED2/ID2 features a 10-bit successive approximation data converter that
functions in either Analog-to-Digital (ADC) or Digital-to-Analog (DAC) mode. A block diagram of
the converter is shown in Figure 20-1. An 8-channel Analog Multiplexer connects seven singleended or three differential voltage inputs from the pins of Port 0 to a sample-and-hold circuit that
in turn provides an input to the successive approximation block. The Sample-and-Hold circuit
ensures that the input voltage to the ADC is held at a constant level during conversion. The SAR
block digitizes the analog voltage into a 10-bit value accessible through a data register. The
SAR block also operates in reverse to generate an analog voltage on Port 2 from a 10-bit digital
value.
ADC results are available in the DADL and DADH register pair. The ADC result scale is determined by the reference voltage (VREF) generated either internally from a 1.0V reference or
externally from VDD/2. The ADC results are always represented in signed 2’s complement form,
with single-ended voltage channels referring to the level above or below VDD/2. The 10-bit
results may be right or left adjusted within the 16-bit register. The sign is extended through the 6
MSBs of right-adjusted results and the 6 LSBs of left-adjusted results are zeroed. If only 8-bit
precision is required, the user should select left-adjusted by setting LADJ in DADC and read only
the DADH register. Example results are listed in Table 20-1.
The conversion formulas are as follows:
(Singled-Ended)
(Differential)
V IN –  V DD  2 
ADC = 511  ------------------------------------V REF
V IN+ – V INADC = 511  --------------------------V REF
Conversion results can be converted into unsigned binary by adding 02h to DADH in rightadjusted mode or 80h to DADH in left-adjusted mode. When using the external reference
(VDD/2) in single-ended mode this is equivalent to:
(Unsigned Singled-Ended)
168
V IN
ADC = 1023  ---------V DD
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
To convert the unsigned binary value back to 2’s complement, subtract 02h from DADH in rightadjusted mode or 80h from DADH in left-adjusted mode. Note that the DADH/DADL registers
cannot be directly manipulated as they are read-only in ADC mode and write-only in DAC mode.
Figure 20-1. DADC Block Diagram
INTERRUPT
FLAG
Timer
Overflows
8-BIT DATA BUS
15
7R
ACK0
ACK2
ACK1
ADIF
LADJ
DAC
ADCE
GO
TRG1
TRG0
ACS1
ACS0
DIFF
ACS2
ACON
IREF
VDD
0
ADC DATA REGISTER
(DADH/DADL)
ADC CTRL & STATUS
REGISTER (DADC)
ADC INPUT SELECT
REGISTER (DADI)
R
VDD/8
R
CHANNEL SELECTION
VDD/2
R
PRESCALER
TRIGGER
SELECT
GND
VREF
INTERNAL
1.0V
REFERENCE
IREF
P0.6
TEMP
START
VDD/8
DA+
P0.5
SAMPLE &
HOLD
P0.4
POS.
INPUT
MUX
P0.3
VIN+
+
10-BIT SAR
-
P0.2
P0.1
DA-
P0.0
NEG.
INPUT
MUX
VIN-
VDD/2
169
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 20-1.
20.1
Example ADC Conversion Codes
Right Adjust
Left Adjust
Single-Ended Mode (VIN)
Differential Mode (VIN+ – VIN-)
0
0
VDD/2
0
0100h
4000h
VDD/2 + 1/2 x VREF
1/2 x VREF
01FFh
7FC0h
VDD/2 + 511/512 x VREF
511/512 x VREF
FF00h
C000h
VDD/2 – 1/2 x VREF
–1/2 x VREF
FE01h
8040h
VDD/2 – 511/512 x VREF
–511/512 x VREF
ADC Operation
The ADC converts an analog input voltage to a 10-bit signed digital value through successive
approximation. When DIFF (DADI.3) is zero, the ADC operates in single-ended mode and the
input voltage is the difference between the voltage at the input pin and VDD/2. In differential
mode (DIFF = 1) the input voltage is the difference between the positive and negative input pins.
The minimum value represents zero difference and the maximum values represent a difference
of positive or negative VREF minus 1 LSB.
The analog input channel is selected by writing to the ACS bits in DADI. The first six Port 0 input
pins can be selected as single-ended inputs to the ADC. Three pairs of Port 0 pins can be
selected as differential inputs.The ACON bit (DADI.7) must be set to one to connect the input
pins to the ADC. Prior to changing ACS, ACON must be cleared to zero. This ensures that
crosstalk between channels is limited. ACON must be set back to one after ACS is updated.
ACON and ACS should not be changed while a conversion is in progress. ADC input channels
must have their port pins configured for input-only mode. The AT89LP51RD2/ED2/ID2 also
includes an on-chip temperature sensor and voltage supply channel. These features are available when ACS = 6. See Section 20.2.
The equivalent model for the analog input circuitry is illustrated in Figure 20-2. An analog source
applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regardless of
whether that channel is selected as input to the ADC. When the channel is selected, the source
must drive the S/H capacitor through the series resistance (combined resistance in the input
path). To achieve 10-bit resolution the S/H capacitor must be charged to within 1/2 LSB of the
expected value within the 1 ADC clock period sample time. High impedance sources may
require a reduction in the ADC clock frequency to achieve full resolution.
Figure 20-2. Equivalent Analog Input Model
RIN =
10 kΩ
RMUX =
10 kΩ
ADCn
CPIN =
10 pF
CS/H =
2 pF
The ADC is enabled by setting the ADCE bit in DADC. Some settling time is required for the reference circuits to stabilize after the ADC is enabled. The ADC does not consume power when
ADCE is cleared, so it is recommended to switch off the ADC before entering power saving
modes.
170
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
A timing diagram of an ADC conversion is shown in Figure 20-3. The conversion requires 13
ADC clock cycles to complete. The analog input is sampled during the third cycle of the conversion and is held constant for the remainder of the conversion. At the end of the conversion, the
interrupt flag, ADIF, is set and the result is written to the data registers. An additional 1 ADC
clock cycle and up to 2 system clock cycles may be required to synchronize ADIF with the rest of
the system. The results in DADH/DADL remain valid until the next conversion completes. DADH
and DADL are read-only registers during ADC mode.
Figure 20-3. ADC Timing Diagram
One Conversion
Cycle Number
1
2
3
4
5
6
7
8
Next Conversion
9
10
11
12
13
1
2
3
ADC Clock
GO/BSY
ADIF
DADH
MSB of Result
DADL
LSB of Result
Sample & Hold
Initialize Circuitry
20.2
Conversion
Complete
Initialize
Temperature Sensor
ADC differential input channel 3 is not connected to a port pin. Instead it has a connection to two
internal special functions: a temperature sensor and a voltage supply monitor. When DIFF = 1
and ACS = 3 the IREF bit in DADI selects between them, such that IREF = 0 selects the voltage
supply channel and IREF = 1 select the temperature sensor channel. Both these modes use the
internal 1.0V reference for the full scale and the negative input. The temperature sensor outputs
a voltage that is proportional to the ambient operating temperature. The uncalibrated output is
linear and is suitable for relative temperature measurements. The supply voltage channel is the
device supply level divided-by-8. It can be used to find the actual operating voltage of the device.
The following conversion formulae apply for temperature sensor and supply monitor modes:
(Temp Sensor)
(Supply Voltage)
20.3
V TEMP – V REF
ADC = 511  -----------------------------------V REF
 VDD  8  – V REF
ADC = 511  ------------------------------------------V REF
DAC Operation
The DAC converts a 10-bit signed digital value to an analog output voltage through successive
approximation. The DAC always operates in differential mode, outputting a voltage differential
between its positive (P2.2) and negative (P2.3) outputs with a common mode of VDD/2. The minimum value represents zero difference and the maximum values represent a difference of
positive or negative VREF minus 1 LSB.
The DAC is enabled by setting the ADCE and DAC bits in DADC and ACON in DADI. Some settling time is required for the reference circuits to stabilize after the DAC is enabled. The DAC
171
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
does not have multiple output channels and the DIFF and ACS bits have no effect in DAC mode.
P2.2 and P2.3 are automatically forced to input-only mode while the DAC is enabled.
A timing diagram of a DAC conversion is shown in Figure 20-4. The conversion requires 13 ADC
clock cycles to complete. Construction of the analog output starts in the second cycle of the conversion and the DAC will allow the new value to propagate to the outputs during cycle 13. At the
end of the conversion, the interrupt flag is set. An additional 1 ADC clock cycle and up to 2 system clock cycles may be required to synchronize ADIF with the rest of the system. The DADL
and DADH registers hold the value to be output and are write-only during DAC mode. An internal
buffer samples DADH/DADL at the start of the conversion and holds the value constant for the
remainder of the conversion. One system clock cycle is required to transfer the contents of
DADH/DADL into the buffer at the start of the conversion and therefore the ADC clock frequency
must always be equal to or less than the system clock frequency during DAC mode to ensure
that the buffer is updated before the second cycle.
Figure 20-4. DAC Timing Diagram
One Conversion
Cycle Number
1
2
3
4
5
6
7
8
Next Conversion
9
10
11
12
13
1
2
3
ADC Clock
GO/BSY
ADIF
DADH
MSB of Output
DADL
LSB of Output
Begin Output
Conversion
Complete
Initialize Circuitry
Initialize
The equivalent model for the analog output circuitry is illustrated in Figure 20-5. The series output resistance of the DAC must drive the pin capacitance and any external load on the pin.
Figure 20-5. Equivalent Analog Output Model
ROUT =
5kΩ
DAn
VOUT
CPIN =
10 pF
AVDD/2
20.4
Clock Selection
The DADC requires a clock of 2 MHz or less to achieve full resolution. By default the DADC will
use an internal 2 MHz clock generated from the 8 MHz internal oscillator. The internal oscillator
will be enabled even if it is not supplying the system clock. This may result in higher power consumption. Conversely, the DADC clock can be generated directly from the system oscillator
using a 7-bit prescaler. The prescaler output is controlled by the ACK bits in DADC as shown in
Figure 20-6. The prescaler is independent of any X2 or CKRL division used for the CPU clock.
172
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
In ADC mode, there are no requirements on the clock frequency with respect to the system
clock. The ADC prescaler selection is independent of the system clock divider and the ADC may
operate at both higher or lower frequencies than the CPU. However, in DAC mode the ADC
clock frequency must not be higher than the CPU clock, including any clock division from the
system clock.
Figure 20-6. DADC Clock Selection
CK/128
CK/64
CK/32
CK/16
CK/8
4
CK/4
INTERNAL
8MHz OSC
CK/2
7-BIT ADC PRESCALER
OSC
ACK0
ACK1
ACK2
ADC CLOCK SOURCE
20.5
Starting a Conversion
Setting the GO/BSY bit (DADC.6) when ADCE = 1 starts a single conversion in both ADC and
DAC modes. The bit remains set while the conversion is in progress and is cleared by hardware
when the conversion completes. The ADC channel should not be changed while a conversion is
in progress.
Alternatively, a conversion can be started automatically by various timer sources. Conversion
trigger sources are selected by the TRG bits in DADI. A conversion is started every time the
selected timer overflows, allowing for conversions to occur at fixed intervals. The GO/BSY bit will
be set by hardware while the conversion is in progress. Note that the timer overflow rate must be
slower than the conversion time.
20.6
Noise Considerations
Digital circuitry inside and outside the device generates EMI which might affect the accuracy of
analog measurements. If conversion accuracy is critical, the noise level can be reduced by
applying the following techniques:
• Keep analog signal paths as short as possible. Make sure to run analog signals tracks over
an analog ground plane, and keep them well away from high-speed digital tracks.
• Place the CPU in Idle during a conversion. For best results, use a Timer to start the
conversion while CPU is already in Idle Mode.
• If any Port 0 pins are used as digital I/Os, it is essential that these do not switch while a
conversion is in progress.
173
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
20.7
Registers
Table 20-2.
DADC – DADC Control Register
DADC = A4H
Reset Value = 0000 0000B
Not Bit Addressable
Bit
ADIF
GO/BSY
DAC
ADCE
LADJ
ACK2
ACK1
ACK0
7
6
5
4
3
2
1
0
Symbol
Function
ADIF
ADC Interrupt Flag
Set by hardware when a conversion completes. Cleared by hardware when calling the interrupt service routine.
GO/BSY
Conversion Start/Busy Flag
In software triggered mode, writing a 1 to this bit starts a conversion. The bit remains high while the conversion is in
progress and is cleared by hardware when the conversion completes. In hardware triggered mode, this bit is set and
cleared by hardware to flag when the DADC is busy.
DAC
Digital-to-Analog Conversion Enable
Set to configure the DADC in Digital-to-Analog (DAC) mode. Clear to configure the DADC in Analog-to-Digital (ADC)
mode.
ADCE
DADC Enable
Set to enable the DADC. Clear to disable the DADC.
LADJ
Left Adjust Enable
When cleared, the ADC results are right adjusted and the MSBs are sign extended. When set, the ADC results are left
adjusted and the LSBs are zeroed.
ACK2-0
DADC Clock Select
Note:
174
ACK3
ACK1
ACK0
Clock Source(1)
0
0
0
Internal RC Oscillator/4 (2MHz)
0
0
1
fOSC/2
0
1
0
fOSC/4
0
1
1
fOSC/8
1
0
0
fOSC/16
1
0
1
fOSC/32
1
1
0
fOSC/64
1
1
1
fOSC/128
1. fOSC is the frequency of the system clock oscillator source before the X1/X2 and CKRL dividers.
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 20-3.
DADI – DADC Input Control Register
DADI = A5H
Reset Value = 0000 0000B
Not Bit Addressable
ACON
IREF
TRG1
TRG0
DIFF
ACS2
ACS1
ACS0
7
6
5
4
3
2
1
0
Bit
Symbol
Function
ACON
Analog Input Connect
When cleared, the analog inputs are disconnected from the ADC and the opamps are disabled. When set, the analog
inputs selected by ACS2-0 are connected to the ADC and the opamps are enabled. ACON must be zero when changing
the input channel multiplexor (ACS2-0). ACON must remain one while a conversion (ADC or DAC) is ongoing.
IREF
Internal Reference Enable
When set, the DADC uses the internal voltage reference. When cleared the DADC uses VDD for its reference.
DIFF
Differential Mode Enable
Set to configure the ADC in differential mode. Clear to configure the ADC in single-ended mode.
TRG1-0
Trigger Select
ACS2-0
Note:
TRG1
TRG0
Trigger
0
0
Software (GO bit)
0
1
Timer 0 Overflow
1
0
Timer 1 Overflow
1
1
Timer 2 Overflow
ADC Channel Select
DIFF
ACS2
ACS1
ACS0
V+
V-
0
0
0
0
P0.0
VDD/2
0
0
0
1
P0.1
VDD/2
0
0
1
0
P0.2
VDD/2
0
0
1
1
P0.3
VDD/2
0
1
0
0
P0.4
VDD/2
0
1
0
1
P0.5
VDD/2
0
1
1
0
reserved
0
1
1
1
P0.6
VDD/2
1
0
0
0
P0.0
P0.1
1
0
0
1
P0.2
P0.3
1
0
1
0
P0.4
P0.5
1
0
1
1
VTEMP(1)
VREF
1
1
X
X
reserved
1. VTEMP is provided by the temperature sensor when IREF = 1. Otherwise VTEMP = VDD/8 when IREF = 0.
175
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 20-4.
DADL – DADC Data Low Register
DADL = ACH
Reset Value = 0000 0000B
Not Bit Addressable
LADJ = 0
ADC.7
ADC.6
ADC.5
ADC.4
ADC.3
ADC.2
ADC.1
ADC.0
LADJ = 1
ADC.1
ADC.0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
Note:
When LADJ = 0, bits 7–0 of the ADC result are found in bits 7–0 of DADL.
When LADJ = 1, bits 1–0 of the ADC result are found in bits 7–6 of DADL. Bits 5–0 are cleared to zero.
Table 20-5.
DADH – DADC Data High Register
DADH = ADH
Reset Value = 0000 0000B
Not Bit Addressable
LADJ = 0
ASGN
ASGN
ASGN
ASGN
ASGN
ASGN
ADC.9
ADC.8
LADJ = 1
ADC.9
ADC.8
ADC.7
ADC.6
ADC.5
ADC.4
ADC.3
ADC.2
Bit
7
6
5
4
3
2
1
0
Note:
176
When LADJ = 0, bits 9–8 of the ADC result are found in bits 1–0 of DADH. Bits 7–2 are signed extended copies of bit 1. i.e.
ASGN = ADC.9
When LADJ = 1, bits 9–2 of the ADC result are found in bits 7–0 of DADH.
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
21. Instruction Set Summary
The AT89LP51RD2/ED2/ID2 is fully binary compatible with the 8051 instruction set. In Compatibility mode the AT89LP51RD2/ED2/ID2 has identical execution time with AT89C51RD2/ED2
and other standard 8051s. The difference between the AT89LP51RD2/ED2/ID2 in Fast mode
and the standard 8051 is the number of cycles required to execute an instruction. Fast mode
instructions may take 1 to 5 clock cycles to complete. The execution times of most instructions
may be computed using Table 21-1. Note that for the purposes of this table, a clock cycle is one
period of the output of the system clock divider. For Fast mode the divider defaults to 1, so the
clock cycle equals the oscillator period. For Compatibility mode the divider defaults to 2, so the
clock cycle is twice the oscillator period, or conversely the clock count is half the number of oscillator periods.
Table 21-1.
Instruction Execution Times and Exceptions(1)
Generic Instruction Types
Fast Mode Cycle Count Formula
Most arithmetic, logical, bit and transfer instructions
# bytes
Branches and Calls
# bytes + 1
Single Byte Indirect (i.e. ADD A, @Ri, etc.)
2
RET, RETI
4
MOVC
3
MOVX
4(3)
MUL
2
DIV
4
MAC
9
INC DPTR
2
Clock Cycles
Arithmetic
Bytes
Compatibility
Fast
Hex Code
ADD A, Rn
1
6
1
28-2F
ADD A, direct
2
6
2
25
ADD A, @Ri
1
6
2
26-27
ADD A, #data
2
6
2
24
ADDC A, Rn
1
6
1
38-3F
ADDC A, direct
2
6
2
35
ADDC A, @Ri
1
6
2
36-37
ADDC A, #data
2
6
2
34
SUBB A, Rn
1
6
1
98-9F
SUBB A, direct
2
6
2
95
SUBB A, @Ri
1
6
2
96-97
SUBB A, #data
2
6
2
94
INC Rn
1
6
1
08-0F
INC direct
2
6
2
05
INC @Ri
1
6
2
06-07
INC A
2
6
2
04
177
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 21-1.
Instruction Execution Times and Exceptions(1) (Continued)
DEC Rn
1
6
1
18-1F
DEC direct
2
6
2
15
DEC @Ri
1
6
2
16-17
DEC A
2
6
2
14
INC DPTR
1
12
2
A3
INC /DPTR(2)
2
18
3
A5 A3
MUL AB
1
24
2
A4
DIV AB
1
24
4
84
DA A
1
6
1
D4
MAC AB(2)
2
–
9
A5 A4
CLR M(2)
2
–
2
A5 E4
ASR M(2)
2
–
2
A5 03
LSL M(2)
2
–
2
A5 23
Clock Cycles
178
Logical
Bytes
Compatibility
Fast
Hex Code
CLR A
1
6
1
E4
CPL A
1
6
1
F4
ANL A, Rn
1
6
1
58-5F
ANL A, direct
2
6
2
55
ANL A, @Ri
1
6
2
56-57
ANL A, #data
2
6
2
54
ANL direct, A
2
6
2
52
ANL direct, #data
3
12
3
53
ORL A, Rn
1
6
1
48-4F
ORL A, direct
2
6
2
45
ORL A, @Ri
1
6
2
46-47
ORL A, #data
2
6
2
44
ORL direct, A
2
6
2
42
ORL direct, #data
3
12
3
43
XRL A, Rn
1
6
1
68-6F
XRL A, direct
2
6
2
65
XRL A, @Ri
1
6
2
66-67
XRL A, #data
2
6
2
64
XRL direct, A
2
6
2
62
XRL direct, #data
3
12
3
63
RL A
1
6
1
23
RLC A
1
6
1
33
RR A
1
6
1
03
RRC A
1
6
1
13
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 21-1.
Instruction Execution Times and Exceptions(1) (Continued)
SWAP A
1
6
1
C4
Clock Cycles
Data Transfer
Bytes
Compatibility
Fast
Hex Code
MOV A, Rn
1
6
1
E8-EF
MOV A, direct
2
6
2
E5
MOV A, @Ri
1
6
2
E6-E7
MOV A, #data
2
6
2
74
MOV Rn, A
1
6
1
F8-FF
MOV Rn, direct
2
12
2
A8-AF
MOV Rn, #data
2
6
2
78-7F
MOV direct, A
2
6
2
F5
MOV direct, Rn
2
12
2
88-8F
MOV direct, direct
3
12
3
85
MOV direct, @Ri
2
12
2
86-87
MOV direct, #data
3
12
3
75
MOV @Ri, A
1
6
1
F6-F7
MOV @Ri, direct
2
12
2
A6-A7
MOV @Ri, #data
2
6
2
76-77
MOV DPTR, #data16
3
12
3
90
MOV /DPTR, #data16(2)
4
–
4
A5 90
MOVC A, @A+DPTR
1
12
3
93
MOVC A, @A+/DPTR(2)
2
–
4
A5 93
MOVC A, @A+PC
1
12
3
83
MOVX A, @Ri
1
12
2
E2-E3
MOVX A, @DPTR
1
12(3)
4(3)
E0
MOVX A, @/DPTR(2)
2
18(3)
5(3)
A5 E0
MOVX @Ri, A
1
12
2
F2-F3
MOVX @DPTR, A
1
12(3)
4(3)
F0
MOVX @/DPTR, A(2)
2
18(3)
5(3)
A5 F0
PUSH direct
2
12
2
C0
POP direct
2
12
2
D0
XCH A, Rn
1
6
1
C8-CF
XCH A, direct
2
6
2
C5
XCH A, @Ri
1
6
2
C6-C7
XCHD A, @Ri
1
6
2
D6-D7
Clock Cycles
Bit Operations
Bytes
Compatibility
Fast
Hex Code
CLR C
1
6
1
C3
CLR bit
2
6
2
C2
179
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 21-1.
Instruction Execution Times and Exceptions(1) (Continued)
SETB C
1
6
1
D3
SETB bit
2
6
2
D2
CPL C
1
6
1
B3
CPL bit
2
6
2
B2
ANL C, bit
2
12
2
82
ANL C, bit
2
12
2
B0
ORL C, bit
2
12
2
72
ORL C, /bit
2
12
2
A0
MOV C, bit
2
6
2
A2
MOV bit, C
2
12
2
92
Clock Cycles
Branching
Bytes
Compatibility
Fast
Hex Code
JC rel
2
12
3
40
JNC rel
2
12
3
50
JB bit, rel
3
12
4
20
JNB bit, rel
3
12
4
30
JBC bit, rel
3
12
4
10
JZ rel
2
12
3
60
JNZ rel
2
12
3
70
SJMP rel
2
12
3
80
ACALL addr11
2
12
3
11,31,51,71,91,
B1,D1,F1
LCALL addr16
3
12
4
12
RET
1
12
4
22
RETI
1
12
4
32
AJMP addr11
2
12
3
01,21,41,61,81,
A1,C1,E1
LJMP addr16
3
12
4
02
JMP @A+DPTR
1
12
2
73
JMP @A+PC(2)
2
12
3
A5 73
CJNE A, direct, rel
3
12
4
B5
CJNE A, #data, rel
3
12
4
B4
CJNE Rn, #data, rel
3
12
4
B8-BF
CJNE @Ri, #data, rel
3
12
4
B6-B7
CJNE A, @R0, rel(2)
3
18
4
A5 B6
CJNE A, @R1, rel(2)
3
18
4
A5 B7
DJNZ Rn, rel
2
12
3
D8-DF
DJNZ direct, rel
3
12
4
D5
NOP
1
6
1
00
Notes:
180
1. A clock cycle is one period of the output of the system clock divider. For Fast mode the divider
defaults to 1, so the clock cycle equals the oscillator period. For Compatibility mode the divider
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
defaults to 2, so the clock cycle is twice the oscillator period, or conversely the clock count is
half the number of oscillator periods.
2. This escaped instruction is an extension to the instruction set.
3. This is the minimum time for MOVX with no wait states. In Compatibility mode an additional 24
clocks are added for the wait state. In Fast mode, 1 clock is added for each wait state (0–3).
21.1
Instruction Set Extensions
The following instructions are extensions to the standard 8051 instruction set that provide
enhanced capabilities not found in standard 8051 devices. All extended instructions start with an
A5H escape code. For this reason random A5H reserved codes should not be placed in the
instruction stream even though other devices may have treated these as NOPs.
Other AT89LP devices may not support all of these instructions.
21.1.1
ASR M
Function: Shift MAC Accumulator Right Arithmetically
Description: The forty bits in the M register are shifted one bit to the right. Bit 39 retains its value to preserve the sign of the
value. No flags are affected.
Example: The M register holds the value 0C5B1A29384H . The following instruction,
ASR M
leaves the M register holding the value 0E2D8D149C2H.
Bytes: 2
Cycles: 2
Encoding:
A5
0
0
0
0
0
0
1
1
Operation: ASR
(Mn)  (Mn + 1) n = 0 - 38
(M39)  (M39)
21.1.2
BREAK
Function: Software Breakpoint (Halt execution)
Description: BREAK transfers control from normal execution to the On-Chip Debug (OCD) handler if OCD is enabled. The PC
is left pointing to the following instruction. If OCD is disabled, BREAK acts as a double NOP. No flags are
affected.
Example: If On-Chip Debugging is allowed, the following instruction,
BREAK
will halt instruction execution prior to the immediately following instruction. If debugging is not allowed, the
BREAK is treated as a double NOP.
Bytes: 2
Cycles: 2
Encoding:
A5
0
0
0
0
0
0
0
0
Operation: BREAK
(PC)  (PC) + 2
181
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
21.1.3
CJNE A, @Ri, rel
Function: Compare and Jump if Not Equal
Description: CJNE compares the magnitudes of the Accumulator and indirect RAM location and branches if their values are
not equal. The branch destination is computed by adding the signed relative-displacement in the last instruction
byte to the PC, after incrementing the PC to the start of the next instruction. The carry flag is set if the unsigned
integer value of ACC is less than the unsigned integer value of the indirect location; otherwise, the carry is
cleared. Neither operand is affected.
Example: The Accumulator contains 34H. Register 0 contains 78H and 78H contains 56H. The first instruction in the
sequence,
CJNE A, @R0, NOT_EQ
;
. . . . . . ...... ...... ; ACC = @R0.
NOT_EQ:
JC
REQ_LOW .. ;IF ACC< @R0.
;
. . . . . . ...... ...... ;ACC > @R0.
sets the carry flag and branches to the instruction at label NOT_EQ. By testing the carry flag, the second
instruction determines whether ACC is greater or less than the location pointed to by R0.
Bytes: 2
Cycles: 9
Encoding:
A5
1
0
1
1
0
1
1
i
rel. address
Operation: CJNE
(PC)  (PC) + 3
IF (A)  ((Ri))
THEN
(PC)  (PC) + relative offset
IF (A) < ((Ri))
THEN
(C)  1
ELSE
(C)  0
21.1.4
CLR M
Function: Clear MAC Accumulator
Description: CLR M clears the 40-bit M register. No flags are affected.
Example: The M registercontains 123456789AH. The following instruction,
CLR M
leaves the M register set to 0000000000H.
Bytes: 2
Cycles: 2
Encoding:
A5
1
1
1
0
0
1
0
0
Operation: JMP
(M)  0
182
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
21.1.5
INC /DPTR
Function: Increment Alternate Data Pointer
Description: INC /DPTR increments the unselected 16-bit data pointer by 1. A 16-bit increment (modulo 216 ) is performed,
and an overflow of the low-order byte of the data pointer from 0FFH to 00H increments the high-order byte. No
flags are affected.
Example: Registers DP1H and DP1L contain 12H and 0FEH, respectively, and DPS = 0. The following instruction
sequence,
INC
INC
INC
/DPTR
/DPTR
/DPTR
changes DP1H and DP1L to 13H and 01H.
Bytes: 2
Cycles: 3
Encoding:
A5
1
0
1
0
0
0
1
1
Operation: INC
IF (DPS) = 0
THEN
(DPTR1)  (DPTR1) + 1
ELSE
(DPTR0)  (DPTR0) + 1
21.1.6
JMP @A+PC
Function: Jump indirect relative to PC
Description: JMP @A+PC adds the eight-bit unsigned contents of the Accumulator to the program counter, which is first
incremented by two. This is the address for subsequent instruction fetches. Sixteen-bit addition is performed
(modulo 216): a carry-out from the low-order eight bits propagates through the higher-order bits. The
Accumulator is not altered. No flags are affected.
Example: An even number from 0 to 6 is in the Accumulator. The following sequence of instructions branches to one of four
AJMP instructions in a jump table starting at JMP_TBL.
JMP
JMP_TBL:
AJMP
AJMP
AJMP
AJMP
@A + PC
LABEL0
LABEL1
LABEL2
LABEL3
If the Accumulator equals 04H when starting this sequence, execution jumps to label LABEL2. Because AJMP is
a 2-byte instruction, the jump instructions start at every other address.
Bytes: 2
Cycles: 3
Encoding:
A5
0
1
1
1
0
0
1
1
Operation: JMP
(PC)  (A) + (PC) + 2
183
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
21.1.7
LSL M
Function: Shift MAC Accumulator Left Logically
Description: The forty bits in the M register are shifted one bit to the left. Bit 0 is cleared. No flags are affected.
Example: The M register holds the value 0C5B1A29384H. The following instruction,
LSL M
leaves the M register holding the value 8B63452708H.
Bytes: 2
Cycles: 2
Encoding:
A5
0
0
1
0
0
0
1
1
Operation: LSL
(Mn+1)  (Mn) n = 0 - 38
(M0)  0
21.1.8
MOVC A, @A+/DPTR
Function: Move code byte relative to Alternate Data Pointer
Description: The MOVC instructions load the Accumulator with a code byte or constant from program memory. The address
of the byte fetched is the sum of the original unsigned 8-bit Accumulator contents and the contents of the
unselected Data Pointer. The base register is not altered. Sixteen-bit addition is performed so a carry-out from
the low-order eight bits may propagate through higher-order bits. No flags are affected.
Example: A value between 0 and 3 is in the Accumulator. The following instructions will translate the value in the
Accumulator to one of four values defined by the DB (define byte) directive.
MOV
/DPTR, #TABLE
MOVC A, @A+PC
RET
TABLE:
DB
DB
DB
DB
66H
77H
88H
99H
If the subroutine is called with the Accumulator equal to 01H, it returns with 77H in the Accumulator.
Bytes: 2
Cycles: 4
Encoding:
A5
1
0
0
1
0
0
1
1
Operation: MOVC
IF (DPS) = 0
THEN
(A)  ( (A) + (DPTR1) )
ELSE
(A)  ( (A) + (DPTR0) )
184
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
21.1.9
MAC AB
Function: Multiply and Accumulate
Description: MAC AB multiplies the signed 16-bit integers in the register pairs {AX, A} and {BX, B} and adds the 32-bit product
to the 40-bit M register. The low-order bytes of the 16-bit operands are stored in A and B, and the high-order
bytes in AX and BX respectively. The four operand registers are unaffected by the operation. If the addition of the
product to the accumulated sum in M results in a two's complement overflow, the overflow flag is set; otherwise it
is not cleared. The carry flag is set if the result is negative and cleared if positive.
Example: Originally the Accumulator holds the value 80 (50H). Register B holds the value 160 (0A0H). The instruction,
MAC AB
will give the product 12, 800 (3200H), so B is changed to 32H (00110010B) and the Accumulator is cleared. The
overflow flag is set, carry is cleared.
Bytes: 2
Cycles: 9
Encoding:
A5
1
0
1
0
0
1
0
0
Operation: MAC
(M39-0)  (M) + { (AX), (A) } X { (BX), (B) }
21.1.10
MOV /DPTR, #data16
Function: Load Alternate Data Pointer with a 16-bit constant
Description: MOV /DPTR, #data16 loads the unselected Data Pointer with the 16-bit constant indicated. The third byte is the
high-order byte, while the fourth byte holds the lower-order byte. No flags are affected.
Example: When DPS = 0, the instruction sequence,
MOV DPTR, # 1234H
MOV /DPTR, # 5678H
loads the value 1234H into the first Data Pointer: DPH0 holds 12H and DPL0 holds 34H; and loads the value
5678H into the second Data Pointer: DPH1 hold 56H and DPL1 holds 78H.
Bytes: 2
Cycles: 3
Encoding:
A5
Operation: MOV
IF (DPS) = 0
THEN
(DP1H) 
(DP1L) 
ELSE
(DP0H) 
(DP0L) 
90
immed. data 15-8
immed. data 7-0
#data15-8
#data7-0
#data15-8
#data7-0
185
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
21.1.11
MOVX A, @/DPTR
Function: Move External using Alternate Data Pointer
Description: The MOVX instruction transfers data from external data memory to the Accumulator. The unselected Data
Pointer generates a 16-bit address which targets EDATA, FDATA or XDATA.
Example: DPS = 0, DPTR0 contains 0123H and DPTR1 contains 4567H. The following instruction sequence,
MOVX
MOVX
A, @DPTR
@/DPTR, A
copies the data from address 0123H to 4567H.
Bytes: 2
Cycles: 3 (EDATA)
5 (FDATA or XDATA)
Encoding:
A5
1
1
1
0
0
0
0
0
Operation: MOVX
IF (DPS) = 0
(A)  ((DPTR1))
ELSE
(A)  ((DPTR0))
21.1.12
MOVX @/DPTR, A
Function: Move External using Alternate Data Pointer
Description: The MOVX instruction transfer data from the Accumulator to external data memory. The unselected Data Pointer
generates a 16-bit address which targets EDATA, FDATA or XDATA.
Example: DPS = 0, DPTR0 contains 0123H and DPTR1 contains 4567H. The following instruction sequence,
MOVX
MOVX
A, @DPTR
@/DPTR, A
copies the data from address 0123H to 4567H.
Bytes: 2
Cycles: 3 (EDATA)
5 (FDATA or XDATA)
Encoding:
A5
1
1
1
1
0
0
0
0
Operation: MOVX
IF (DPS) = 0
THEN
((DPTR1))  (A)
ELSE
((DPTR0))  (A)
186
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
22. On-Chip Debug System
The AT89LP51RD2/ED2/ID2 On-Chip Debug (OCD) System uses a two-wire serial interface to
control program flow; read, modify, and write the system state; and program the nonvolatile
memory. The OCD System has the following features:
22.1
•
•
•
•
Complete program flow control
Read-Modify-Write access to all internal SFRs and data memories
Four hardware program address breakpoints
Four program/data address breakpoints configurable in 2 maskable pairs.
•
•
•
•
•
•
•
Unlimited program software breakpoints using BREAK instruction
Break on change in program memory flow
Break on stack overflow/underflow
Break on Watchdog overflow
Break on reset
Non-intrusive operation
Programming of nonvolatile memory
Physical Interface
The On-Chip Debug System uses a two-wire synchronous serial interface to establish communication between the target device and the controlling emulator system. The OCD interface is
enabled by clearing the OCD Enable Fuse. The OCD device connections are shown in Figure
22-1. When OCD is enabled, the RST port pin is configured as an input for the Debug Clock
(DCL). P4.3 is a bi-directional data line for the Debug Data (DDA).
When designing a system where On-Chip Debug will be used, the following observations must
be considered for correct operation:
• RST cannot be connected directly to VDD or GND and any external capacitors or supervisors
connected to RST must be removed.
• All external reset sources must be removed.
• OCD is shipped disabled from the factory. A device programmer is required to enable this
fuse before debugging can occur.
• Enabling OCD disables the RST input and thereby disables the In-System Programming
interface (ISP). ISP can only be re-entered by holding RST active at power-up. The
bootloader remains active and has priority over the OCD system.
Figure 22-1. AT89LP51RD2/ED2/ID2 On-Chip Debug Connections
AT89LP51RD2/ED2/ID2
VDD
DCL
RST
GND or VDD
POL
P4.3
DDA
GND
187
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
22.2
Software Breakpoints
The AT89LP51RD2/ED2/ID2 microcontroller includes a BREAK instruction for implementing
program memory breakpoints in software. A software breakpoint can be inserted manually by
placing the BREAK instruction in the program code. Some emulator systems may allow for automatic insertion/deletion of software breakpoints. The Flash memory must be re-programmed
each time a software breakpoint is changed. Frequent insertions/deletions of software breakpoints will reduce the endurance of the nonvolatile memory. Devices used for debugging
purposes should not be shipped to end customers. The BREAK instruction is treated as a twocycle NOP when OCD is disabled.
22.3
Limitations of On-Chip Debug
The AT89LP51RD2/ED2/ID2 is a fully-featured microcontroller that multiplexes several functions
on its limited I/O pins. Some device functionality must be sacrificed to provide resources for OnChip Debugging. The On-Chip Debug System has the following limitations:
• The Debug Clock pin (DCL) is physically located on the same pin as the External Reset
(RST). Therefore, an external reset source is unavailable and must be emulated when OCD
is enabled. The Reset Output feature is also disabled except during POR
• The Debug Data pin DDA is physically located on the same pin as P4.3. The P4.3 I/O
function cannot be emulated in this mode
• The bootloader has priority over OCD. Debugging is not possible when the bootloader is
active (BLJB = 0 or hardware entry triggered)
• Programming of any hardware lockbit will disable OCD
• The OCD pins are not bonded in the 40-pin PDIP package. In order to debug the device, one
of the 44-pin packages must be used
188
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
23. Flash Memory Programming
The Atmel AT89LP51RD2/ED2/ID2 microcontroller features 64K bytes of on-chip In-System
Programmable Flash program memory and 4K bytes of EEPROM data memory. In-System Programming allows programming and reprogramming of the microcontroller positioned inside the
end system. The programmer communicates serially with the AT89LP51RD2/ED2/ID2 microcontroller, reprogramming all nonvolatile memories on the chip. In-System Programming
eliminates the need for physical removal of the chips from the system. This will save time and
money, both during development in the lab, and when updating the software or parameters in
the field. The AT89LP51RD2/ED2/ID2 provides the following programming interfaces:
• High-Speed, four-wire SPI-based programming interface (ISP)
This synchronous hardware interface programs the device while it is in reset and therefore,
does not require the CPU to be operational, i.e. no clock is required except the SPI serial
clock. This interface can be used both in-system and in a stand-alone programmer, and has
full access to all nonvolatile memory resources. This interface is compatible with the Atmel
AT89LP ISP Studio software. See Section 23.6 “In-System Programming (ISP)” on page 217
for more information.
• 12-pin parallel programming interface (PRL)
This interface is a submode of the SPI interface that allows data to be read/written one 8-bit
byte at a time instead of serially 1-bit at a time. This interface is intended only for stand-alone
programmers. An 87C51-compatible parallel interface is not available. See Section 23.6.1
“Physical Interface” on page 217 for more information.
• ROM-based UART serial bootloader (BOOT)
When using this 2-pin asynchronous interface, the device runs a default software bootloader
from an on-chip ROM. The system clock must be operational and will limit the speed at which
the interface functions. This interface is intended for in-system use. It has full access to the
Flash code memory and EEPROM data memory, but does not have access to all
configuration options. This interface is compatible with the Atmel FLIP software. See Section
23.5 “Bootloader” on page 202 for more information.
• User-defined bootloader and/or In-Application Programming (IAP)
The ROM bootloader can call a user-defined bootloader located within the code memory
instead of the default UART bootloader. The user is free to use any available interface to
program the device. The ROM also contains an application programming interface (API) that
implements the low-level routines necessary to perform in-application programming (IAP). It
is recommended that users employ these functions instead of writing their own low-level
routines. Advanced users may wish to implement their own routines in some cases. See
Section 23.4 “In-Application Programming (IAP)” on page 194.
None of the programming interfaces require an external dedicated programming voltage. The
necessary high programming voltage is generated on-chip using the standard VDD pin of the
microcontroller.
Note:
In this document the term Bootloader, or BOOT, is used to when referring to the UART-based
ROM bootloader and In-System Programming, or ISP, is used with reference to the SPI-based
interface. This is different from AT89C51RD2/ED2/ID2 where ISP also referred to the bootloader
(as no SPI programming interface was present). However, it should be noted that both interfaces
are perfectly capable of performing in-system programming, i.e programming the device when it is
already mounted in the final end-user system.
189
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
23.1
Memory Organization
The AT89LP51RD2/ED2/ID2 offers 64K bytes of In-System Programmable nonvolatile Flash
code memory and 4K bytes of nonvolatile EEPROM data memory. In addition, the device contains a 512-byte User Signature Array, a 128-byte read-only Atmel Signature Array and 19 User
Configuration Fuses. The memory organization is shown in Table 23-1 and Figure 23-1. The
code memory and auxiliary memories are divided into pages of 128 bytes each and share a temporary page buffer of 64 bytes (one half page). A single page erase operation will erase an
entire 128-byte page, while a single write operation will only program half of a page. Therefore,
two write operations are required for every erase operation when the whole page must be reprogrammed. This detail is transparent to the user when using the bootloader or Flash API.
The EEPROM data memory has a page size of 32 bytes and its own 32-byte page buffer. The
EEPROM supports erase/write operations on any number of bytes, 1–32, within a page without
affecting the other bytes in that page.
Figure 23-1. AT89LP51RD2/ED2/ID2 Memory Organization
00
3F
Page Buffer
00
3F 40
7F
User Fuse Row
Page 0 Low
Atmel Signature Array
Page 0 Low
Page 0 High
Page 3 Low
Page 2 Low
Page 1 Low
Page 0 Low
Page 3 High
Page 2 High
Page 1 High
Page 511 Low
Page 510 Low
Page 511 High
Page 510 High
OSCCAL
User Signature Array
SSB
BSB
Page 0 High
SBV
FFFF
00
1F
Page Buffer
Code Memory
Page 128
0FFF
Data Memory
Page 1 High
Page 1 High
Page 1 Low
Page 0 Low
00
3F 40
Page 0
0000
7F
00
0000
1F
.
Table 23-1.
190
AT89LP51RD2/ED2/ID2 Memory Organization
Memory
Capacity
Page Size
# Pages
Address Range
Code Flash
65536 bytes
128 bytes
512
0000H – FFFFH
Data EEPROM
4096 bytes
32 bytes
128
0000H – 0FFFH
User Signature
512 bytes
128 bytes
4
0000H – 01FFH
Atmel Signature
128 bytes
128 bytes
1
0200H – 027FH
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
23.1.1
User Signature Array
The AT89LP51RD2/ED2/ID2 includes a 512-byte User Signature Array in four 128-byte pages.
The User Signature Array is available for serial numbers, firmware revision information, date
codes or other user parameters. The User Signature Array may only be written by an external
ISP programmer when the User Signature Programming Fuse is enabled. When the fuse is
enabled, Chip Erase will also erase the third page of the array. When the fuse is disabled, none
of the pages are affected by page erase/write commands and only pages one and two will be
erased by Chip Erase. Table 23-3 summarizes this behavior. Programming of the Signature
Array is also disabled by the Lock Bits. However, reading the signature is always allowed and
the array should not be used to store security sensitive information. The User Signature Array
may be modified during execution through the In-Application Programming interface, regardless
of the state of the User Signature Programming fuse or Lock Bits.
Some locations of the User Signature Array have special meaning for the system as shown in
Table 23-2. Pages one and two store bytes necessary for bootloader operation (See “Bootloader” on page 202). Page three stores a calibration byte for the internal RC Oscillator. This
byte is read at power-up to set the frequency of the oscillator. Other bytes in these pages may
be used as additional signature space; however, care should be taken to preserve the parameter values when modifying other bytes in the same page.
Table 23-2.
User Signature Parameter Bytes
Name
Definition
Location
Default Value
BSB
Boot Status Byte
0000H
FFH
SBV
Software Boot Vector
0001H
FCH (or FFH)
SSB
Software Security Byte
0080H
FFH
OSCCAL
Oscillator Calibration
0180H
(1)
Note:
1. The Oscillator Calibration Byte controls the frequency of the internal RC oscillator. The frequency is inversely proportional to the calibration value such that higher values result in lower
frequencies. A copy of the factory-set calibration value is stored at location 0008H of the Atmel
Signature.
Table 23-3.
Page #
Notes:
User Signature ISP Programming Behavior
Address
Chip Erase
Page Erase
Page Write
(1)
By Fuse(1)
0
0000–007FH
YES
By Fuse
1
0080–00HFH
YES
By Fuse(1)
By Fuse(1)
2
0100–017FH
By Fuse(2)
By Fuse(1)
By Fuse(1)
3
0180–01FFH
NO
By Fuse(1)
By Fuse(1)
1. During ISP, a page erase/write of the user signature is only allowed when the User SIgnature
Programming Fuse is active.
2. Chip Erase will erase this page only if the User SIgnature Programming Fuse is active.
191
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
23.1.2
Atmel Signature Array
The Atmel Signature Array is a 128-byte read-only array that contains the Device ID and related
information. The Device ID values are shown in Table 23-4. A copy of the OSCCAL calibration
byte is also stored at address 0008H.
Table 23-4.
23.2
Device ID Values in Atmel Signature
Device
00H
01H
02H
30H
31H
60H
61H
AT89LP51RD2
1EH
64H
72H
58H
D7H
ECH
EFH
AT89LP51ED2
1EH
64H
65H
58H
D7H
ECH
EFH
AT89LP51ID2
1EH
64H
69H
58H
D7H
ECH
EFH
User Configuration Fuses
The AT89LP51RD2/ED2/ID2 includes 19 user fuses for configuration of the device. Each fuse is
accessed at a separate address in the User Fuse Row, with each byte representing one fuse as
listed in Table 23-5. From a programming standpoint, fuses are treated the same as normal
code bytes except they are not affected by Chip Erase. Fuses can be cleared at any time by writing 00H to the appropriate locations in the fuse row. However, to set a fuse, i.e. write it to FFH
the entire fuse row must be erased and then reprogrammed. The programmer should read the
state of all the fuses into a temporary location, modify those fuses which need to be disabled,
then issue a Fuse Write with Auto-Erase command using the temporary data.
Note that the bootloader only has limited access to the fuses. For full device configuration an
external ISP programmer is required.
Table 23-5.
Address
User Configuration Fuse Definitions
Fuse Name
Description
Selects source for the system clock when using OSCA:
00 – 01H
Clock Source A – CSA[0:1](2)
CSA1
CSA0
Selected Source
FFh
FFh
High Speed Crystal Oscillator on XTAL1A/XTAL2A (XTAL)
FFh
00h
Low Power Crystal Oscillator on XTAL1A/XTAL2A (XTAL)
00h
FFh
External Clock on XTAL1A (XCLK)
00h
00h
Internal 8 MHz RC Oscillator (IRC)
Selects time-out delay for the POR/BOD/PWD wake-up period:
02 – 03H
SUT1
SUT0
Selected Time-out
00h
00h
1 ms (XTAL); 16 µs (XCLK/IRC)
00h
FFh
2 ms (XTAL); 512 µs (XCLK/IRC)
FFh
00h
4 ms (XTAL); 1 ms (XCLK/IRC)
FFh
FFh
16 ms (XTAL); 4 ms (XCLK/IRC)
Start-up Time – SUT[0:1]
04H
Bootloader Jump Bit
FFh: Reset to user application at 0000H
00h: Reset to ROM bootloader at F800H
05H
External RAM Enable
FFh: External RAM enabled at reset (EXTRAM = 1)
00h: External RAM disabled at reset (EXTRAM = 0)
06H
Compatibility Mode
FFh: CPU functions in 12-clock Compatibility mode
00h: CPU functions is single-cycle Fast mode
07H
ISP Enable(3)
FFh: In-System Programming Enabled
00h: In-System Programming Disabled (Enabled at POR only)
192
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 23-5.
User Configuration Fuse Definitions
Address
Fuse Name
Description
08H
X1/X2 Mode
FFh: X1 Mode (System clock is divided-by-two)
00h: X2 Mode (System clock is not divided-by-two)
09H
OCD Enable
FFh: On-Chip Debug is Disabled
00h: On-Chip Debug is Enabled
0AH
User Signature Programming
FFh: Programming of User Signature Disabled
00h: Programming of User Signature Enabled
0BH
Tristate Ports
FFh: I/O Ports start in input-only mode (tristated) after reset
00h: I/O Ports start in quasi-bidirectional mode after reset
0CH
EEPROM Erase
FFh: EEPROM is erased during chiperase
00h: EEPROM is not erased during chiperase
Selects source for the system clock when using OSCA:
0D – 0EH
LPM1
LPM0
Power Mode
FFh
FFh
Low Power Mode
FFh
00h
Normal Mode
00h
FFh
Extra Low Power Mode (FOSC  1 MHz)
00h
00h
Normal Mode
Low Power Mode – LPM[0:1]
0FH
R1 Enable
FFh: 5 M resistor on XTAL1A Disabled
00h: 5 M resistor on XTAL1A Enabled
10H
Oscillator Select
00h: Boot from Oscillator B (AT89LP51ID2 Only)
FFh: Boot from Oscillator A
Selects source for the system clock when using OSCB (AT89LP51ID2 Only):
11 – 12h
Notes:
Clock Source B – CSB[0:1](2)
CSB1
CSB0
Selected Source
FFh
FFh
Low Frequency Crystal Oscillator on XTAL1B/XTAL2B (XTAL)
FFh
00h
Low Frequency Crystal Oscillator on XTAL1B/XTAL2B (XTAL)
00h
FFh
External Clock on XTAL1B (XCLK)
00h
00h
Internal 8 MHz RC Oscillator (IRC)
1. The default state from the factory for all fuses is FFh, except for the Tristate Ports, Bootloader Jump Bit, and External RAM
enable, which are 00H.
2. Changes to these fuses will only take effect after a device POR.
3. Changes to these fuses will only take effect after the ISP session terminates by bringing RST inactive.
23.3
Flash Hardware Security
The AT89LP51RD2/ED2/ID2 provides three Hardware Security Bits (or Lock Bits) for Flash
Code Memory and Data EEPROM security. Security bits can be left unprogrammed (FFh) or
programmed (00h) to obtain the protection levels listed in Table 23-6. Security bits can only be
erased (set to FFh) by Chip Erase. Lock bit mode 2 disables programming of all memory
spaces, including the User Signature Array and User Configuration Fuses. User fuses must be
programmed before enabling Lock bit mode 2 or 3. Lock bit mode 3 implements mode 2 and
also blocks reads from the code and data memories; however, reads of the User Signature
Array, Atmel Signature Array, and User Configuration Fuses are still allowed.
The Hardware Security bits only restrict the access of the SPI-based ISP interface. The Hardware Security Bits will not disable the Bootloader or any programming initiated by the application
software using IAP.
193
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 23-6.
Security Protection Modes
Program Lock Bits (by address)
Mode
00h
01h
02h
Protection Mode
1
FFh
FFh
FFh
No program lock features
2
00h
FFh
FFh
Further programming of the Flash is disabled
3
00h
00h
FFh
Further programming of the Flash is disabled and verify (read) is also disabled
4
00h
00h
00h
Further programming of the Flash is disabled and verify (read) is also disabled;
External execution above 32K when BMS = 1 is disabled
23.4
In-Application Programming (IAP)
The AT89LP51RD2/ED2/ID2 supports In-Application Programming (IAP), allowing the program
memory to be modified during execution. IAP can be used to modify the user application on the
fly or to use program memory for nonvolatile data storage. The AT89LP51RD2/ED2/ID2
includes a Flash Application Programming Interface (API) as part of the bootloader ROM code.
The Flash API is the preferred way to program the Flash memory from the application code.
Advanced users looking to write their own low-level routines should refer to Section 23.4.2 on
page 196.
23.4.1
API Call Description
The In-Application Programming (IAP) feature allows reprogramming a microcontroller on-chip
Flash memory without removing it from the system and while the embedded application is running. The user application can call Flash Application Programming Interface (API) routines
allowing IAP. These Flash API are also executed by the bootloader.
To call the corresponding API, the user may use a set of routines which can be linked with the
application. Example of Flash_api routines are available on the Atmel web site on the software
application note:
C Flash Drivers for the AT89C51RD2/ED2
The API calls description and arguments are shown in Table 23-7.
The application selects an API by setting R1, ACC, DPTR0 and DPTR1 registers. All calls are
made through a common interface “USER_CALL” at the address FFF0h. The jump to the
USER_CALL must be done by an LCALL instruction in order to be able to return to the application. Before jumping to USER_CALL, the bit ENBOOT in AUXR1 register must be set to map the
ROM code into the address space.
Flash API calls have the following constraints:
• The interrupts are not disabled by the bootloader. Interrupts must be disabled by the user
prior to calling USER_CALL, then re-enabled when returning.
• The user must feed the hardware watchdog before launching a Flash operation.
• The API call requires a minimum of two free stack bytes
194
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 23-7.
API Call Summary
Command
R1
A
DPTR0
DPTR1
Returned Value
READ MANUF ID
00h
XXh
0000h
XXh
ACC = Manufacturer
Id
READ DEVICE ID1
00h
XXh
0001h
XXh
ACC = Device Id 1
Read Device identifier 1
READ DEVICE ID2
00h
XXh
0002h
XXh
ACC = Device Id 2
Read Device identifier 2
READ DEVICE ID3
00h
XXh
0003h
XXh
ACC = Device Id 3
Read Device identifier 3
ERASE BLOCK
PROGRAM DATA
BYTE
01h
02h
XXh
Value to
write
Erase block 0
DPH = 20h
Erase block 1
DPH = 40h
00h
None
Erase block 2
DPH = 80h
Erase block 3
DPH = C0h
Erase block 4
Address of
byte to
program
XXh
None
XXh
Program up one data byte in the on-chip
flash memory.
Set SSB level 1
0001h
05h
Read Manufacturer identifier
DPH = 00h
0000h
PROGRAM SSB
Command Effect
Set SSB level 2
00h
None
0010h
Set SSB level 0
0011h
Set SSB level 1
PROGRAM BSB
06h
New BSB
value
0000h
XXh
none
Program boot status byte
PROGRAM SBV
06h
New SBV
value
0001h
XXh
none
Program software boot vector
READ SSB
07h
XXh
0000h
XXh
ACC = SSB
Read Software Security Byte
READ BSB
07h
XXh
0001h
XXh
ACC = BSB
Read Boot Status Byte
READ SBV
07h
XXh
0002h
XXh
ACC = SBV
Read Software Boot Vector
09h
Number of
byte to
program
Address of
the first byte
to program
in the Flash
memory
Address in
XRAM of
the first data
to program
None
Program up to 128 bytes in user Flash.
Remark: number of bytes to program is
limited such as the Flash write remains in
a single 128 bytes page. Hence, when
ACC is 128, valid values of DPL are 00h,
or, 80h.
0Ah
Fuse
value
00h or
01h
0008h
XXh
none
Program X2 fuse bit with ACC
PROGRAM BLJB
FUSE
0Ah
Fuse
value
00h or
01h
0004h
XXh
none
Program BLJB fuse bit with ACC
READ HSB
0Bh
XXh
XXXXh
XXh
ACC = HSB
Read Hardware Byte
READ BOOT ID1
0Eh
XXh
DPL = 00h
XXh
ACC = ID1
Read boot ID1
READ BOOT ID2
0Eh
XXh
DPL = 01h
XXh
ACC = ID2
Read boot ID2
READ BOOT
VERSION
0Fh
XXh
XXXXh
XXh
ACC = Boot_Version
PROGRAM DATA
PAGE
PROGRAM X2 FUSE
Read bootloader version
195
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
23.4.2
Low-Level Interface
The CPU interfaces to the Flash memory through the FCON register (Table 23-10) and EECON
register (Table 3-5 on page 25). These registers are used to:
• Map the memory spaces in the addressable space
• Launch the programming of the memory spaces
• Get the status of the Flash memory (busy/not busy)
CAUTION: The incorrect usage of these functions can make the system unstable or inoperable.
For internal execution from user space the AT89LP51RD2/ED2/ID2 uses an idle-while-write
architecture where the CPU is placed in an idle state while programming occurs. When the write
completes, the CPU will continue executing with the instruction after the instruction that started
the write sequence (usually a MOV to FCON). All peripherals will continue to function during the
write cycle; however, interrupts will not be serviced until the write completes.
For external execution from user space the AT89LP51RD2/ED2/ID2 uses an execute-whilewrite architecture where the CPU continues to operate while the programming occurs. The software should poll the state of the FBUSY flag to determine when the write completes. Interrupts
must be disabled during the write sequence as the CPU will not be able to vector to the internal
interrupt table and care should be taken that the application does not jump to an internal address
until the programming completes.
The Flash API routines in the Boot ROM also use execute-while-write. Interrupts must be disabled before calling the routines to prevent the CPU from vectoring to a non-ROM address
before the programming completes.
Flash memory uses a page-based programming model. Flash data memory differs from traditional EEPROM data memory in the method of writing data. EEPROM generally can update a
single byte with any value. Flash memory splits programming into write and erase operations. A
Flash write can only program zeroes, i.e change ones into zeroes (1  0). Any ones in the write
data are ignored. A Flash erase sets an entire page of data to ones so that all bytes become
FFH. Therefore after an erase, each byte in the page can only be written once with any possible
value. Bytes can be overwritten without an erase as long as only ones are changed into zeroes.
However, if even a single bit needs updating from zero to one (0  1); then the contents of the
page must first be saved, the entire page must be erased and the zero bits in all bytes (old and
new data combined) must be written. Avoiding unnecessary page erases greatly improves the
endurance of the memory.
23.4.2.1
Mapping of the Memory Space
By default, the user application space of the Flash Code memory is accessed read-only by the
MOVC instruction. The Flash temporary page buffer is made accessible (write-only) by setting
the FPS bit in FCON register. Writing is possible from 0000H to FFFFF, address bits 6 to 0 are
used to select an address within a page while bits 15 to 7 are used to select the programming
address of the page. Setting FPS takes precedence over the EXTRAM bit in AUXR.
The other memory spaces (User and Atmel Signatures, User Fuses, Hardware Security) are
made accessible in the code segment by programming bits FMOD0 and FMOD1 in FCON register in accordance with Table 23-8. A MOVC instruction can then be used for reading these
spaces.
196
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 23-8.
Memory Selection
FMOD1
FMOD0
0
0
0
1
Addressable space
User Application (0000–FFFFH)
User Signature (0000–01FFH)
Atmel Signature (0200–027FH read-only)
User Fuses (0000–007FH)
1
0
Hardware Security Bits (0080–00FFH read-only)
1
23.4.2.2
1
Reserved
Launching Programming
The FPL bits in the FCON register are used to secure the launch of programming. A specific
sequence must be written in these bits to unlock the write protection and to launch the programming. This sequence is 5xH followed by AxH. Table 23-9 summarizes the programming of the
memory spaces according to the FMOD bits.
Table 23-9.
Programming Sequences
Write to FCON
Memory
User Application
(CODE)
FPL3-0
FPS
FMOD1
FMOD0
Operation
5
X
0
0
No action
A
X
0
0
Write the page buffer to user space
(0000–FFFFH)
5
X
0
1
No action
A
X
0
1
Write the page buffer to User
Signature space (0000–01FFH)
5
X
1
0
No action
A
X
1
0
Write the page buffer to User Fuse
space (0000–007FH)
5
X
1
1
No action
A
X
1
1
No action
User Signature
User Fuses
Reserved
Notes:
1. The sequence 5xH and AxH must be executing without instructions between them otherwise
the programming is aborted.
2. Interrupts that may occur during programming time must be disabled to avoid any spurious exit
of the programming mode.
23.4.2.3
Status of the Flash Memory
The bit FBUSY in FCON register is used to indicate the status of programming. FBUSY is set
when programming is in progress and cleared when the programming completes. If programming was interrupted due to a brown-out condition the ERR flag in EECON is set.
23.4.2.4
Loading the Page Buffer
The AT89LP51RD2/ED2/ID2 includes a temporary page buffer of 64 bytes, or one half of a
page. Because the page buffer is 64 bytes long, the maximum number of bytes written at one
time is 64. Therefore, two write cycles are required to fill an entire 128-byte page, one for the low
half page (00H–3FH) and one for the high half page (40H–7FH) as shown in Figure 23-2.
197
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 23-2. Page Programming Structure
00
3F
Page Buffer
Data Memory
Low Half Page
00
High Half Page
3F 40
7F
Any number of data bytes from 1 to 64 can be loaded into the temporary page buffer. This provides the capability to program the whole memory by byte, by half-page or by any number of
bytes in a half-page. Note that once loaded, a buffer location cannot be reloaded with another
value. The page buffer is automatically cleared after each erase/write operation.
By default no erase is performed prior to writing the page buffer contents to the Flash array. Any
unloaded locations remain unchanged. Any zeroes in the loaded locations will be written to the
desired page. The auto-erase bit AERS (EECON.6) can be set to one to perform a page erase
automatically at the beginning of any write sequence. The page erase will erase the entire page,
i.e. both the low and high half pages. However, the write operation paired with the auto-erase
can only program one of the half pages. A second write cycle without auto-erase is required to
update the other half page. When AERS = 1 any unloaded locations will be left blank (FFH) after
the operation completes.
The following procedure is used to load the page buffer and is summarized in Figure 23-3:
1.
2.
3.
4.
5.
6.
7.
23.4.2.5
Save then disable interrupts (EA = 0)
Map the page buffer space by setting FPS = 1
Load the DPTR (or /DPTR) with the address to load
Load Accumulator register with the data to load
Execute the MOVX @DPTR, A instruction (or MOVX @/DPTR, A instruction)
If needed loop the steps 3—5 until the page buffer is completely loaded
Unmap the page buffer (FPS = 0) and restore interrupts (EA = 1)
Programming the Flash Code Space
The following procedure is used to program the User code space and is summarized in Figure
23-4:
1. Load up to one half-page of data in the page buffer from address 0000H to FFFFH
2. Save then disable the interrupts (EA = 0)
3. Launch the programming by writing the data sequence 50H followed by A0H to FCON
register
4. If launched from internal memory, the CPU idles until programming completes. If
launched from external memory, poll the FBUSY flag until it is cleared
5. Restore the interrupts (EA = 1)
198
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 23-3. Flash Page Buffer Loading Procedure
Flash Page Buffer
Loading
Save and Disable IT
EA = 0
Page Buffer Mapping
FCON = 08h (FPS=1)
Data Load
DPTR = Address
ACC = Data
Exec: MOVX @DPTR, A
Last Byte
to load?
Data memory Mapping
FCON = 00h (FPS = 0)
Restore IT
Note:
23.4.2.6
The last page address used when loading the page buffer is the one used to select the page programming address.
Programming the User Signature Space
The following procedure is used to program the User Signature space and is summarized in Figure 23-4:
1. Load up to one half-page of data in the page buffer from address 0000H to 01FFH
2. Save then disable the interrupts (EA = 0)
3. Launch the programming by writing the data sequence 52H followed by A2H to FCON
register.
4. If launched from internal memory, the CPU idles until programming completes. If
launched from external memory, poll the FBUSY flag until it is cleared
5. Restore the interrupts (EA = 1)
199
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 23-4. Flash Programming Procedure
Flash Spaces
Programming
Page Buffer Loading
see Figure 23-3
Save and Disable IT
EA = 0
Launch Programming
FCON = 5xh
FCON = Axh
FBusy
Cleared?
Clear Mode
FCON = 00h
End Programming
Restore IT
23.4.2.7
Programming the User Fuse Space
The following procedure is used to program the User Fuse space and is summarized in Figure
23-4:
1. Load up to one half-page of data in the page buffer from address 0000H to 01FFH
2. Save then disable the interrupts (EA = 0)
3. Launch the programming by writing the data sequence 54H followed by A4H to FCON
register.
4. If launched from internal memory, the CPU idles until programming completes. If
launched from external memory, poll the FBUSY flag until it is cleared
5. Restore the interrupts (EA = 1)
23.4.2.8
Reading the Flash Code Space
The following procedure is used to read the User code space:
1. Map the code space by writing 00H to FCON (the default)
2. Read one byte in Accumulator by executing MOVC A,@A+DPTR where A+DPTR is the
address of the code byte to read
200
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
23.4.2.9
Reading the User/Atmel Signature
The following procedure is used to read the User or Atmel Signature space and is summarized
in Figure 23-5:
• Map the Signature space by writing 02H to FCON register
• Read one byte in Accumulator by executing MOVC A,@A+DPTR where A+DPTR is 0000–
01FFH for the User Signature and 0200–027FH for the Atmel Signature
• Clear FCON to unmap the Signature space
23.4.2.10
Reading the User Fuses/Hardware Security Bits
The following procedure is used to read the User Fuses or Hardware Security space and
is summarized in Figure 23-5:
• Map the User Fuses/Hardware Security space by writing 04H in FCON register
• Read one byte in Accumulator by executing MOVC A,@A+DPTR where A+DPTR is 0000–
007FH for the User Fuses and 0080–00FFH for the Hardware Security
• Clear FCON to unmap the User Fuses/Hardware Security
Figure 23-5. Reading Procedure
Flash Spaces Reading
Flash Spaces Mapping
FCON = 00000aa0
Data Read
DPTR = Address
ACC = 0
Exec: MOVC A, @A+DPTR
Clear Mode
FCON = 00h
Note:
aa = 00B for the User Application Code
aa = 01B for the User/Atmel Signature
aa = 10B for the User Fuses/Hardware Security
201
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 23-10. FCON – Flash Control Register
FCON Address = 0D1H
Reset Value = xxxx 000xB
Not Bit Addressable
Bit
FPL3
FPL2
FPL1
FPL0
FPS
FMOD1
FMOD0
FBUSY
7
6
5
4
3
2
1
0
Symbol
Function
FPL3-0
Programming Launch Command Bits
Write 5Xh followed by AXh to launch the programming according to FMOD1-0.
FPS
Flash Map Program Space
Set this bit to direct the MOVX @DPTR, A and MOVX @/DPTR, A instructions to the Flash memory temporary page
buffer. Clear to allow MOVX to write regular data memory.
Flash Mode
Mode
FMOD1-0
FBUSY
23.5
FMOD1
FMOD0
Memory Operation Target
0
0
0
CODE space (0000–FFFFH)
1
0
1
User Signature space (0000–01FFH)
Atmel Signature space (0200–027FH read-only)
2
1
0
User Fuse space (0000–007FH)
Hardware Security space (0080–00FFH read-only)
3
1
1
Reserved
Flash Busy
Set by hardware when programming is in progress. Cleared by hardware when programming is done. Cannot be
changed by software.
Bootloader
The Bootloader is a ROM-based application that provides the following features:
• Flash EEPROM Internal Program Memory
• Boot vector allows user provided Flash loader code to reside anywhere in the Flash memory
space. This configuration provides flexibility to the user.
• Default loader in Boot ROM allows programming via the serial port without the need of a user
provided loader.
• Programming and erasing voltage with standard power supply
• Read/Programming/Erase:
– Byte-wise read without wait state
– Byte or page erase and programming (10 ms)
• Typical programming time (64K bytes) is 22s with on chip serial bootloader
• Programmable security for the code in the Flash
• 100K write cycles
• 10 years data retention
The bootloader manages communication according to a specifically defined protocol to provide
the whole access and service on Flash memory. Furthermore, all accesses and routines can be
called from the user application.
202
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 23-6. Diagram Context Description
Access Via
Specific
Protocol
Bootloader
Flash Memory
Access From
User
Application
Table 23-11 list some acronyms used by the Bootloader.
Table 23-11. Bootload Definitions
Mnemonic
Definition
BSB
Boot Status Byte
HW/HSB
Hardware Byte/Hardware Security Byte
SBV
Software Boot Vector
SSB
Software Security Byte
On Figure 23-7, the on-chip bootloader processes are:
• ISP Communication Management
The purpose of this process is to manage the communication and its protocol between the
on-chip bootloader and a external device. The on-chip ROM implements a serial protocol
(see section “Bootloader Protocol Description” on page 208). This process translate serial
communication frame (UART) into Flash memory access (read, write, erase, etc.).
• User Call Management
Several Application Program Interface (API) calls are available for use by an application
program to permit selective erasing and programming of Flash pages. All calls are made
through a common interface (API calls), included in the ROM bootloader. The programming
functions are selected by setting up the microcontroller’s registers before making a call to a
common entry point (0xFFF0). Results are returned in the registers. The purpose on this
process is to translate the registers values into internal Flash Memory Management. See “InApplication Programming (IAP)” on page 194
• Flash Memory Management
This process manages low level access to Flash memory (performs read and write access).
203
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 23-7. Bootloader Functional Description
External Host with
Specific Protocol
Communication
User
Application
User Call
Management (API)
ISP Communication
Management
Flash Memory
Management
Flash
Memory
23.5.1
Bootloader Process
The bootloader can be activated by two means: Hardware conditions or regular boot process.
The Hardware condition PSEN = 0 during the deassertion of RST (falling edge for POL = 1, rising edge for POL = 0) forces the on-chip bootloader execution. This allows an application to be
built that will normally execute the end user’s code but can be manually forced into default Bootloader operation. As PSEN is a an output port in normal operating mode after reset, user
application should take care to release PSEN after the validating edge of the reset signal. The
hardware condition is sampled at the reset edge, and thus can be released at any time when the
reset input is inactive. To ensure correct microcontroller startup, the PSEN pin should not be tied
to ground during power-on (See Figure 23-8).
Figure 23-8. Hardware condition typical sequence during power-on (POL = 1)
VCC
PSEN
RST
204
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
The on-chip bootloader boot process is shown Figure 23-9 on page 206 and described in Table
23-12.
Table 23-12. Bootloader Process Description
Purpose
23.5.2
23.5.2.1
Hardware Condition
The Hardware Condition forces the bootloader execution whatever the
BLJB, BSB and SBV values.
BLJB
The Boot Loader Jump Bit forces the application execution.
BLJB = 0 => Bootloader execution
BLJB = 1 => Application execution
The BLJB is a User configuration fuse. It can be modified by hardware
(programmer) or by software (API). Note: The BLJB test is performed by
hardware to prevent any program execution.
SBV
The Software Boot Vector contains the high address of customer
bootloader stored in the application.
SBV = FCh (default value) if no customer bootloader in user Flash.
Note: The customer bootloader is called by JMP [SBV]00h instruction.
Bootloader Resources
Several on-chip resources are provided for use by the bootloader.
Hardware Register
The hardware register of the AT89LP51RD2/ED2/ID2 is called the Hardware Byte or Hardware
Security Byte (HSB). It is a shadow of selected resources from the User Fuses and Hardware
Security Bits.
Table 23-13. Hardware Security Byte (HSB)
7
6
5
4
3
2
1
0
X2
BLJB
-
-
XRAM
LB2
LB1
LB0
Bit
Number
Bit
Mnemonic
7
X2
6
BLJB
Boot Loader Jump Bit
Unprogrammed (‘1’ value) to start the user’s application on next reset at address 0000h.
Programmed (‘0’ value) to start the boot loader at address F800h on next reset (Default).
5
OSC
Oscillator Bit
Programmed to allow oscillator B at startup
Unprogrammed this bit to allow oscillator A at startup (Default).
4
-
3
XRAM
XRAM config bit (only programmable by programmer tools)
Programmed to inhibit XRAM.
Unprogrammed, this bit to valid XRAM (Default).
2-0
LB2-0
User Memory Lock Bits (only programmable by programmer tools)
See Table 23-14
Description
X2 Mode
Programmed (‘0’ value) to force X2 mode after reset.
Unprogrammed (‘1’ Value) to force X1 mode after reset (Default).
Reserved
205
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 23-9. Bootloader Process
RESET
If BLJB = 0 then ENBOOT Bit (AUXR1) is Set
else ENBOOT Bit (AUXR1) is Cleared
Yes (PSEN = 0, EA = 1, and ALE =1 or Not Connected)
Hardware
Hardware
Condition?
BLJB = 1
ENBOOT = 0
BLJB!= 0
?
Software
BLJB = 0
ENBOOT = 1
BSB = 00h
?
PC = 0000h
User Application
SBV = FCh
?
USER BOOT LOADER
Atmel BOOT LOADER
PC= [SBV]00h
206
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
23.5.2.2
Flash Memory Lock Bits
The three lock bits provide different levels of protection for the on-chip code and data when programmed as shown in Table 23-14. These bits in the HSB are copies of the Hardware Security
Bits (See Section 23.3 on page 193).
Table 23-14. Program Lock Bits
Program Lock Bits
Security
Level
LB0
LB1
LB2
1
U
U
U
No program lock features enabled.
Note:
23.5.2.3
Protection Description
2
P
U
U
MOVC instruction executed from external program memory is disabled from
fetching code bytes from internal memory, EA is sampled and latched on reset,
and further parallel programming of the on chip code memory is disabled.
ISP and software programming with API are still allowed.
3
X
P
U
Same as 2, also verify code memory through parallel programming interface is
disabled.
4
X
X
P
Same as 3, also external execution is disabled (Default).
U: Unprogrammed or "one" level.
P: Programmed or "zero" level.
X: Do not care
WARNING: Security level 2 and 3 should only be programmed after Flash and code verification.
Software Registers
Several registers are used in by the bootloader for the boot process. These registers are in the
User Signature part of the Flash memory. They are accessed in the following ways:
• Commands issued by the ISP programmer
• Commands issued by the Bootloader software.
• API calls issued by the application software.
Several software registers are described in Table 23-15.
Table 23-15. Bootloader Software Registers
Mnemonic
Definition
Default value
SBV
Software Boot Vector
FCh
BSB
Boot Status Byte
FFh
SSB
Software Security Byte
FFh
After programming the part by the bootloader, the BSB must be cleared (00h) in order to allow
the application to boot at 0000h.
The content of the Software Security Byte (SSB) is described in Table 23-16 and Table 23-17.
The SSB protects the Flash memory from programming by the bootloader the same way the
Hardware Security bits protect from ISP.
207
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 23-16. Software Security Byte
7
6
5
4
3
2
1
0
-
-
-
-
-
-
LB1
LB0
Bit
Number
Bit
Mnemonic
Description
7
-
Reserved
Do not clear this bit.
6
-
Reserved
Do not clear this bit.
5
-
Reserved
Do not clear this bit.
4
-
Reserved
Do not clear this bit.
3
-
Reserved
Do not clear this bit.
2
-
Reserved
Do not clear this bit.
1-0
LB1-0
User Memory Lock Bits
See Table 23-17
The two lock bits provide different levels of protection for the on-chip code and data, when programmed as shown in Table 23-17.
Table 23-17.
User Memory Lock Bits of the SSB
Program Lock Bits
Security
Level
LB0
LB1
1
1
1
No program lock features enabled.
2
0
1
Bootloader programming of the Flash is disabled.
3
X
0
Same as 2, also verify through Bootloader programming interface is disabled.
Note:
23.5.3
23.5.3.1
Protection Description
X: Do not care
WARNING: Security level 2 and 3 should only be programmed after Flash verification.
Bootloader Protocol Description
Physical Layer
The UART used to transmit information has the following configuration:
• Character: 8-bit data
• Parity: none
• Stop: 2 bits
• Flow control: none
• Baud Rate: autobaud is performed by the bootloader to compute the baud rate chosen by the
host.
208
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
23.5.3.2
Frame Description
The Serial Protocol is based on the Intel Hex-type records.
Intel Hex records consist of ASCII characters used to represent hexadecimal values and are
summarized below.
Figure 23-10. Intel Hex Type Frame
Record
Mark
’:’
Reclen
Load
Offset
Record
Type
Data
or
Info
1-byte
1-byte
2-bytes
1-byte
n-bytes
Checksum
1-byte
• Record Mark:
Record Mark is the start of frame. This field must contain ’:’.
• Reclen:
Reclen specifies the number of bytes of information or data which follows the Record Type
field of the record.
• Load Offset:
Load Offset specifies the 16-bit starting load offset of the data bytes, therefore this field is
used only for Data Program Record (see Section “Bootloader Command Summary”).
• Record Type:
Record Type specifies the command type. This field is used to interpret the remaining
information within the frame. The encoding for all the current record types is described in
Section “Bootloader Command Summary”.
• Data/Info:
Data/Info is a variable length field. It consists of zero or more bytes encoded as pairs of
hexadecimal digits. The meaning of data depends on the Record Type.
• Checksum:
The two’s complement of the 8-bit bytes that result from converting each pair of ASCII
hexadecimal digits to one byte of binary, and including the Reclen field to and including the
last byte of the Data/Info field. Therefore, the sum of all the ASCII pairs in a record after
converting to binary, from the Reclen field to and including the Checksum field, is zero.
23.5.4
23.5.4.1
Functional Description
Software Security Bits (SSB)
The SSB protects any Flash access from Bootloader commands. The command "Program Software Security Bit" can only write a higher priority level. There are three levels of security:
• level 0: NO_SECURITY (FFh)
This is the default level.From level 0, one can write level 1 or level 2.
• level 1: WRITE_SECURITY (FEh)
For this level it is impossible to write in the Flash memory, BSB or SBV. The Bootloader
returns ’P’ on write access. From level 1, one can write only level 2.
• level 2: RD_WR_SECURITY (FCh)
Level 2 forbids all read and write accesses to/from the Flash/EEPROM memory. The
Bootloader returns ’L’ on read or write access. Only a full chip erase in parallel mode (using a
programmer) or ISP command can reset the software security bits. From level 2, one cannot
read and write anything.
209
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 23-18. Software Security Byte Behavior
23.5.4.2
Level 0
Level 1
Level 2
Flash/EEPROM
Any access allowed
Read-only access allowed
Any access not allowed
Fuse Bit
Any access allowed
Read-only access allowed
Any access not allowed
BSB & SBV
Any access allowed
Read-only access allowed
Any access not allowed
SSB
Any access allowed
Write level 2 allowed
Read-only access allowed
Manufacturer Info
Read-only access allowed
Read-only access allowed
Read-only access allowed
Bootloader Info
Read-only access allowed
Read-only access allowed
Read-only access allowed
Erase Block
Allowed
Not allowed
Not allowed
Full Chip Erase
Allowed
Allowed
Allowed
Blank Check
Allowed
Allowed
Allowed
Full Chip Erase
The ISP command "Full Chip Erase" erases all user Flash memory (fills with FFh) and sets
some bytes used by the bootloader at their default values:
• BSB = FFh
• SBV = FCh
• SSB = FFh
The Full Chip Erase does not affect the bootloader or the EEPROM.
23.5.4.3
23.5.5
23.5.5.1
Checksum Error
When a checksum error is detected, ‘X’ is sent followed with CR&LF.
Flow Description
Overview
An initialization step must be performed after each Reset. After microcontroller reset, the bootloader waits for an autobaud sequence (see section “Autobaud Performance” ). After the
communication is initialized, the protocol depends on the record type requested by the host.
FLIP, a software utility to implement bootloader programming with a PC, is available from the
Atmel web site.
23.5.5.2
Communication Initialization
The host initializes the communication by sending a ’U’ character to help the bootloader to compute the baud rate (autobaud).
Figure 23-11. Initialization
Host
210
Bootloader
Init Communication
"U"
If (Not Received "U")
Else
Communication Opened
"U"
Performs Autobaud
Sends Back “U” Characte
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
23.5.5.3
Autobaud Performance
The bootloader feature allows a wide range of baud rates in the user application. It is also adaptable to a wide range of oscillator frequencies. This is accomplished by measuring the bit-time of
a single bit in a received character. This information is then used to program the baud rate in
terms of timer counts based on the oscillator frequency. The bootloader feature requires that an
initial character (an uppercase U) be sent to the AT89LP51RD2/ED2/ID2 to establish the baud
rate. Table 23-19 shows the autobaud capability.
For AT89LP51ID2 the bootloader always uses OSCA. If the device boots on OSCB, the bootloader will enable and switch to OSCA. In this case both the OSCA and OSCB sources must be
operational, i.e. a crystal or external clock source must be connected to the oscillator inputs
unless the oscillator source was previously configured as the internal RC oscillator.
Table 23-19. Autobaud Performance
Frequency
(MHz)
Baudrate (kHz)
1.8432
2
2.4576
3
3.6864
4
5
6
7.3728
2400
OK
OK
OK
OK
OK
OK
OK
OK
OK
4800
OK
-
OK
OK
OK
OK
OK
OK
OK
9600
OK
-
OK
OK
OK
OK
OK
OK
OK
19200
OK
-
OK
OK
OK
-
-
OK
OK
38400
-
-
OK
OK
-
OK
OK
OK
57600
-
-
-
-
OK
-
-
-
OK
115200
-
-
-
-
-
-
-
-
OK
Frequency
(MHz)
Baudrate (kHz)
8
10
11.0592
12
14.746
16
20
24
26.6
2400
OK
OK
OK
OK
OK
OK
OK
OK
OK
4800
OK
OK
OK
OK
OK
OK
OK
OK
OK
9600
OK
OK
OK
OK
OK
OK
OK
OK
OK
19200
OK
OK
OK
OK
OK
OK
OK
OK
OK
38400
-
-
OK
OK
OK
OK
OK
OK
OK
57600
-
-
OK
-
OK
OK
OK
OK
OK
115200
-
-
OK
-
OK
-
-
-
-
211
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
23.5.5.4
Command Data Stream Protocol
All commands are sent using the same flow. Each frame sent by the host is echoed by the
bootloader.
Figure 23-12. Command Flow
Host
Bootloader
":"
Sends First Character of the
Frame
If (not received ":")
":"
Else
Sends Echo and Start
Reception
Sends Frame (made of 2 ASCII
Characters Per Byte)
Echo Analysis
23.5.6
Gets Frame, and Sends Back Echo
for Each Received Byte
Write/Program Commands Description
This flow is common to the following frames:
• Flash/EEPROM Programming Data Frame
• EOF or Atmel Frame (only Programming Atmel Frame)
• Config Byte Programming Data Frame
• Baud Rate Frame
Figure 23-13. Write/Program Flow
Bootloader
Host
Send Write Command
Write Command
Wait Write Command
OR
Wait Checksum Error
Checksum Error
’X’ & CR & LF
Send Checksum Error
COMMAND ABORTED
NO_SECURITY
OR
Wait Security Error
’P’ & CR & LF
Send Security Error
COMMAND ABORTED
Wait Programming
Wait COMMAND_OK
’.’ & CR & LF
Send COMMAND_OK
COMMAND FINISHED
212
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Example:
Programming Data (write 55h at address 0010h in the Flash)
HOST
: 01 0010 00 55 9A
BOOTLOADER
: 01 0010 00 55 9A . CR LF
Programming Atmel function (write SSB to level 2)
HOST
: 02 0000 03 05 01 F5
BOOTLOADER
: 02 0000 03 05 01 F5. CR LF
Writing Frame (write BSB to 55h)
23.5.7
HOST
: 03 0000 03 06 00 55 9F
BOOTLOADER
: 03 0000 03 06 00 55 9F . CR LF
Blank Check Command Description
Figure 23-14. Blank Check Flow
Bootloader
Host
Send Blank Check Command
Blank Check Command
Wait Blank Check Command
OR
Checksum Error
Wait Checksum Error
’X’ & CR & LF
Send Checksum Error
COMMAND ABORTED
Flash Blank
OR
Wait COMMAND_OK
’.’ & CR & LF
Send COMMAND_OK
COMMAND FINISHED
address & CR & LF
Wait Address not
Erased
Send First Address
not Erased
COMMAND FINISHED
Example:
Blank Check ok
HOST
: 05 0000 04 0000 7FFF 01 78
BOOTLOADER
: 05 0000 04 0000 7FFF 01 78 . CR LF
Blank Check ok at address xxxx
HOST
: 05 0000 04 0000 7FFF 01 78
BOOTLOADER
: 05 0000 04 0000 7FFF 01 78 xxxx CR LF
Blank Check with checksum error
HOST
: 05 0000 04 0000 7FFF 01 70
BOOTLOADER
: 05 0000 04 0000 7FFF 01 70 X CR LF CR LF
213
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
23.5.8
Display Data Description
Figure 23-15. Display Flow
Bootloader
Host
Send Display Command
Display Command
Wait Display Command
OR
Checksum error
Wait Checksum Error
’X’ & CR & LF
Send Checksum Error
COMMAND ABORTED
RD_WR_SECURITY
OR
Wait Security Error
’L’ & CR & LF
Send Security Error
COMMAND ABORTED
Read Data
All Data Read
Complet Frame
"Address = "
"Reading Value"
CR & LF
Wait Display Data
Send Display Data
All Data Read
All Data Read
COMMAND FINISHED
COMMAND FINISHED
Example:
Display data from address 0000h to 0020h
HOST
214
: 05 0000 04 0000 0020 00 D7
BOOTLOADER
: 05 0000 04 0000 0020 00 D7 CR LF
BOOTLOADER
0000=-----data------ CR LF (16 data)
BOOTLOADER
0010=-----data------ CR LF (16 data)
BOOTLOADER
0020=data CR LF
( 1 data)
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
23.5.9
Read Function Description
This flow is similar for the following frames:
• Reading Frame
• EOF Frame/ Atmel Frame (only reading Atmel Frame)
Figure 23-16. Read Flow
Bootloader
Host
Read Command
Send Read Command
Wait Read Command
OR
Checksum error
Wait Checksum Error
’X’ & CR & LF
Send Checksum error
COMMAND ABORTED
RD_WR_SECURITY
OR
Wait Security Error
’L’ & CR & LF
Send Security error
COMMAND ABORTED
Read Value
’value’ & ’.’ & CR & LF
Wait Value of Data
Send Data Read
COMMAND FINISHED
Example:
Read function (read SBV)
HOST
: 02 0000 05 07 02 F0
BOOTLOADER
: 02 0000 05 07 02 F0 Value . CR LF
Atmel Read function (read Bootloader version)
HOST
: 02 0000 01 02 00 FB
BOOTLOADER
: 02 0000 01 02 00 FB Value . CR LF
215
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
23.5.10 Bootloader Command Summary
Table 23-20. Bootloader Command Summary
Command
Command Name
00h
Program Code
Data[0]
Write Function
Command Effect
Program Nb Code Byte.
Bootloader will accept up to 128 (80h) data bytes. The data
bytes should be 128 byte page flash boundary.
00h
Erase block0 (0000h-1FFFh)
20h
Erase block1 (2000h-3FFFh)
40h
Erase block2 (4000h-7FFFh)
80h
Erase block3 (8000h- BFFFh)
C0h
Erase block4 (C000h- FFFFh)
03h
00h
Hardware Reset
04h
00h
Erase SBV & BSB
00h
Program SSB level 1
01h
Program SSB level 2
00h
Program BSB (value to write in data[2])
01h
Program SBV (value to write in data[2])
-
Full Chip Erase (This command needs about 6 sec to be
executed)
10h(1)
Program OSC fuse (value to write in data[2])
04h
Program BLJB fuse (value to write in data[2])
08h
Program X2 fuse (value to write in data[2])
01h
03h
Data[1]
05h
06h
07h
0Ah
04h
Display Function
Data[0:1] = start address
Data [2:3] = end address
Data[4] = 00h:Display Code
Data[4] = 01h: Blank check
Data[4] = 02h: Display EEPROM
Display Code
Blank Check
Display EEPROM data
00h
Manufacturer Id
01h
Device Id #1
02h
Device Id #2
03h
Device Id #3
00h
Read SSB
01h
Read BSB
02h
Read SBV
06h
Read Extra Byte
00h
Read Hardware Byte
00h
Read Device Boot ID1
01h
Read Device Boot ID2
00h
Read Bootloader Version
00h
05h
Read Function
07h
0Bh
0Eh
0Fh
07h
Note:
216
Program Nn EEprom Data Byte.
Bootloader will accept up to 128 (80h) data bytes.
Program EEPROM data
1. AT89C51ID2 Only. This byte differs from AT89C51ID2, which uses 02h
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
23.6
In-System Programming (ISP)
The Atmel AT89LP51RD2/ED2/ID2 microcontroller features 64K bytes of on-chip In-System
Programmable Flash program memory and 4K bytes of nonvolatile EPROM data memory. InSystem Programming allows programming and reprogramming of the microcontroller positioned
inside the end system. Using a simple 4-wire SPI interface, the programmer communicates serially with the AT89LP51RD2/ED2/ID2 microcontroller, reprogramming all nonvolatile memories
on the chip. In-System Programming eliminates the need for physical removal of the chips from
the system. This will save time and money, both during development in the lab, and when updating the software or parameters in the field. The programming interface of the
AT89LP51RD2/ED2/ID2 includes the following features:
• Four-wire serial SPI Programming Interface or 12-pin Parallel Interface
• Selectable Polarity Reset Entry into Programming
• User Signature Array
• Flexible Page Programming
• Row Erase Capability
• Page Write with Auto-Erase Commands
• Programming Status Register
For more detailed information on In-System Programming, refer to the Application Note entitled
“AT89LP In-System Programming Specification”.
23.6.1
Physical Interface
The AT89LP51RD2/ED2/ID2 provides a standard programming command set with two physical
interfaces: a bit-serial and a byte-parallel interface. Normal Flash programming utilizes the Serial
Peripheral Interface (SPI) pins of an AT89LP51RD2/ED2/ID2 microcontroller. The SPI is a fullduplex synchronous serial interface consisting of four wires: Serial Clock (SCK), MasterIn/Slave-out (MISO), Master-out/Slave-in (MOSI) and Slave Select (SS). When programming an
AT89LP51RD2/ED2/ID2 device, the programmer always operates as the SPI master, and the
target system always operates as the SPI slave. To enter or remain in Programming mode the
device’s reset line (RST) must be held active. With the addition of VDD and GND, an
AT89LP51RD2/ED2/ID2 microcontroller can be programmed with a minimum of eight connections as shown in Figure 23-17.
Figure 23-17. In-System Programming Device Connections
AT89LP51RD2/ED2/ID2
Serial Clock
P1.7/SCK
Serial Out
P1.6/MISO
Serial In
P1.5/MOSI
SS
P1.4/SS
VDD
POL
GND or VDD
RST
RST
GND
217
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
The Parallel interface is a special mode of the serial interface, i.e. the serial interface is used to
enable the parallel interface. After enabling the interface serially over P1.7/SCK and P1.5/MOSI,
P1.5 is reconfigured as an active-low output enable (OE) for data on Port 0. When OE = 1, command, address and write data bytes are input on Port 0 and sampled at the rising edge of SCK.
When OE = 0, read data bytes are output on Port 0 and should be sampled on the falling edge of
SCK. The P1.7/SCK and RST pins continue to function in the same manner. With the addition of
VDD and GND, the parallel interface requires a minimum of fourteen connections as shown in
Figure 23-18. Note that a connection to P1.6/MISO is not required for using the parallel
interface.
Figure 23-18. Parallel Programming Device Connections
AT89LP51RD2/ED2/ID2
Clock
RST
P1.7/SCK
RST
VDD
OE
P1.5/MOSI
POL
SS
P1.4/SS
P0.7-0
GND or VDD
8
Data In/Out
GND
The Programming Interface is a means of externally programming the AT89LP51RD2/ED2/ID2
microcontroller. The Interface can be used to program the device both in-system and in a standalone serial programmer. The Interface does not require any clock other than SCK and is not
limited by the system clock frequency. During Programming the system clock source of the target device can operate normally.
When designing a system where In-System Programming will be used, the following observations must be considered for correct operation:
• The ISP interface uses the SPI clock mode 0 (CPOL = 0, CPHA = 0) exclusively with a
maximum frequency of 5 MHz.
• The AT89LP51RD2/ED2/ID2 will enter programming mode only when its reset line (RST) is
active. To simplify this operation, it is recommended that the target reset can be controlled by
the In-System programmer. To avoid problems, the In-System programmer should be able to
keep the entire target system reset for the duration of the programming cycle. The target
system should never attempt to drive the three SPI lines while reset is active.
• The ISP Enable Fuse must be set to allow programming during any reset period. If the ISP
Fuse is disabled, ISP may only be entered at POR. To enter programming the RST pin must
be driven active prior to the end of Power-On Reset (POR). After POR has completed the
device will remain in ISP mode until RST is brought inactive. Once the initial ISP session has
ended, the power to the target device must be cycled OFF and ON to enter another session.
Note that if this method is required, an active-low reset polarity is recommended.
• For standalone programmers, an active-low reset polarity is recommended (POL = 0). RST
may then be tied directly to GND to ensure correct entry into Programming mode regardless
of the device settings.
218
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
23.6.2
Command Format
Programming commands consist of two preamble bytes, an opcode byte, two address bytes,
and zero or more data bytes. Figure 23-19 on page 219 shows a simplified flow chart of a command sequence.
A sample command packet is shown in Figure 23-20 on page 220. The SS pin defines the
packet frame. SS must be brought low before the first byte in a command is sent and brought
back high after the final byte in the command has been sent. The command is not complete until
SS returns high. Command bytes are issued serially on MOSI. Data output bytes are received
serially on MISO. Packets of variable length are supported by returning SS high when the final
required byte has been transmitted. In some cases command bytes have a don’t care value.
Don’t care bytes in the middle of a packet must be transmitted. Don’t care bytes at the end of a
packet may be ignored.
Page oriented instructions always include a full 16-bit address. The higher order bits select the
page and the lower order bits select the byte within that page. The AT89LP51RD2/ED2/ID2 allocates 6 bits for byte address, 1 bit for low/high half page selection and 9 bits for page address.
The half page to be accessed is always fixed by the page address and half select as transmitted.
The byte address specifies the starting address for the first data byte. After each data byte has
been transmitted, the byte address is incremented to point to the next data byte. This allows a
page command to linearly sweep the bytes within a page. If the byte address is incremented
past the last byte in the half page, the byte address will roll over to the first byte in the same half
page. While loading bytes into the page buffer, overwriting previously loaded bytes will result in
data corruption.
For a summary of available commands, see Table 23-21 on page 221.
Figure 23-19. Command Sequence Flow Chart
Input Preamble 1
(AAh)
Input Preamble 2
(55h)
Input Opcode
Input Address
High Byte
Input Address
Low Byte
Input/Output
Data
Address +1
219
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 23-20. ISP Command Packet (Serial)
SS
SCK
MOSI
7 6 5 4 3 2 1 0
7 6 5 4 3 2 1 0
7 6 5 4 3 2 1 0
Preamble 1
Preamble 2
Opcode
Address High
Address Low
Data In
X
X
X
X
X
7 6 5 4 3 2 1 0
MISO
7 6 5 4 3 2 1 0
Data Out
Figure 23-21. ISP Command Packet (Parallel)
SS
SCK
WRITE
OE
P0
AAh
55h
Opcode
Address High
Address Low
Data In
READ
OE
P0
220
AAh
55h
Opcode
Address High
Address Low
Data Out
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 23-21. Programming Command Summary
Command
Opcode
Addr High
Addr Low
Data 0
Data n
Program Enable(1)
1010 1100
0101 0011
–
–
–
Parallel Enable(2)
1010 1100
0011 0101
–
–
–
Chip Erase
1000 1010
–
–
–
–
Read Status
0110 0000
xxxx xxxx
xxxx xxxx
Status Out
Load Page Buffer(3)
0101 0001
xxxx xxxx
00bb bbbb
Data In 0 ... Data In n
Write Code Page(3)
0101 0000
aaaa aaaa
asbb bbbb
Data In 0 ... Data In n
Write Code Page with Auto-Erase(3)
0111 0000
aaaa aaaa
asbb bbbb
Data In 0 ... Data In n
Read Code Page(3)
0011 0000
aaaa aaaa
asbb bbbb
Data Out 0 ... Data Out n
Write Data Page(3)
1101 0000
000a aaaa
asbb bbbb
Data In 0 ... Data In n
Write Data Page with Auto-Erase(3)
1101 0010
000a aaaa
asbb bbbb
Data In 0 ... Data In n
Read Data Page(3)
1011 0000
000a aaaa
asbb bbbb
Data Out 0 ... Data Out n
Write User Fuses(3)(4)(5)
1110 0001
0000 0000
00bb bbbb
Data In 0 ... Data In n
Write User Fuses with Auto-Erase(3)(4)(5)
1111 0001
0000 0000
00bb bbbb
Data In 0 ... Data In n
Read User Fuses(3)(4)(5)
0110 0001
0000 0000
00bb bbbb
Data Out 0 ... Data Out n
Write Lock Bits(3)(4)(6)
1110 0100
0000 0000
00bb bbbb
Data In 0 ... Data In n
Read Lock Bits(3)(4)(6)
0110 0100
0000 0000
00bb bbbb
Data Out 0 ... Data Out n
Write User Signature Page(3)
0101 0010
0000 0000
asbb bbbb
Data In 0 ... Data In n
Write User Signature Page with Auto-Erase(3)
0111 0010
0000 0000
asbb bbbb
Data In 0 ... Data In n
Read User Signature Page(3)
0011 0010
0000 0000
asbb bbbb
Data Out 0 ... Data Out n
Read Atmel Signature Page(3)
0011 1000
0000 0000
0sbb bbbb
Data Out 0 ... Data Out n
Notes:
1. Program Enable must be the first command issued after entering into programming mode.
2. Parallel Enable switches the interface from serial to parallel format until RST returns high.
3. Any number of Data bytes from 1 to 64 may be written/read. The internal address is incremented between each byte.
4. Each byte address selects one fuse or lock bit. Data bytes must be 00h or FFh.
5. See Table 23-5 on page 192 for Fuse definitions.
6. See Table 23-6 on page 194 for Lock Bit definitions.
7. Symbol Key:
a:
Page Address Bit
s:
Half Page Select Bit
b:
Byte Address Bit
x:
Don’t Care Bit
221
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
23.6.3
Status Register
The current state of the memory may be accessed by reading the status register. The status register is shown in Table 23-22.
Table 23-22. Status Register
Bit
–
–
–
–
LOAD
SUCCESS
WRTINH
BUSY
7
6
5
4
3
2
1
0
Symbol
Function
LOAD
Load flag. Cleared low by the load page buffer command and set high by the next memory write. This flag signals that
the page buffer was previously loaded with data by the load page buffer command.
SUCCESS
Success flag. Cleared low at the start of a programming cycle and will only be set high if the programming cycle
completes without interruption from the brownout detector.
WRTINH
Write Inhibit flag. Cleared low by the brownout detector (BOD) whenever programming is inhibited due to VDD falling
below the minimum required programming voltage. If a BOD episode occurs during programming, the SUCCESS flag
will remain low after the cycle is complete.
BUSY
Busy flag. Cleared low whenever the memory is busy programming or if write is currently inhibited.
23.6.4
DATA Polling
The AT89LP51RD2/ED2/ID2 implements DATA polling to indicate the end of a programming
cycle. While the device is busy, any attempted read of the last byte written will return the data
byte with the MSB complemented. Once the programming cycle has completed, the true value
will be accessible. During Erase the data is assumed to be FFH and DATA polling will return
7FH. When writing multiple bytes in a page, the DATA value will be the last data byte loaded
before programming begins, not the written byte with the highest physical address within the
page.
23.6.5
23.6.5.1
Programming Interface Timing
This section details general system timing sequences and constraints for entering or exiting InSystem Programming as well as parameters related to the Serial Peripheral Interface during
ISP. The general timing parameters for the following waveform figures are listed in section “Timing Parameters” on page 225.
Power-up Sequence
Execute this sequence to enter programming mode immediately after power-up. In the RST pin
is disabled or if the ISP Fuse is disabled, this is the only method to enter programming (see
“External Reset” on page 57).
1. Apply power between VDD and GND pins. RST should remain low.
2. Wait at least tPWRUP. and drive RST high if active-high otherwise keep low.
3. Wait at least tSUT for the internal Power-on Reset to complete. The value of tSUT will
depend on the current settings of the device.
4. Start programming session.
222
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 23-22. Serial Programming Power-up Sequence
VDD
tPWRUP
RST
tPOR + tSUT
SS
tZSS
SCK
23.6.5.2
MISO
HIGH Z
MOSI
HIGH Z
Power-down Sequence
Execute this sequence to power-down the device after programming.
1.
2.
3.
4.
5.
Drive SCK low.
Wait at least tSSD and Tristate MOSI.
Wait at least tRHZ and drive RST low.
Wait at least tSSZ and tristate SCK.
Wait no more than tPWRDN and power off VDD.
Figure 23-23. Serial Programming Power-down Sequence
VDD
tPWRDN
RST
SS
SCK
23.6.5.3
tSSD
tSSZ
MISO
HIGH Z
MOSI
HIGH Z
ISP Start Sequence
Execute this sequence to exit CPU execution mode and enter ISP mode when the device has
passed Power-On Reset and is already operational.
1.
2.
3.
4.
Drive RST high.
Wait tRLZ + tSTL.
Drive SCK low.
Start programming session.
223
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 23-24. In-System Programming (ISP) Start Sequence
tRLZ
VDD
XTAL1
RST
tSTL
SS
tZSS
tSSE
SCK
23.6.5.4
MISO
HIGH Z
MOSI
HIGH Z
ISP Exit Sequence
Execute this sequence to exit ISP mode and resume CPU execution mode.
1.
1.
2.
3.
4.
Drive SCK low.
Wait at least tSSD.
Tristate MOSI.
Wait at least tRHZ and bring RST low.
Wait tSSZ and tristate SCK.
Figure 23-25. In-System Programming (ISP) Exit Sequence
VDD
XTAL1
RST
tSSZ
SS
SCK
Note:
23.6.5.5
224
tRHZ
tSSD
MISO
HIGH Z
MOSI
HIGH Z
The waveforms on this page are not to scale.
Serial Peripheral Interface
The Serial Peripheral Interface (SPI) is a byte-oriented full-duplex synchronous serial communication channel. During In-System Programming, the programmer always acts as the SPI master
and the target device always acts as the SPI slave. The target device receives serial data on
MOSI and outputs serial data on MISO. The Programming Interface implements a standard
SPI Port with a fixed data order and For In-System Programming, bytes are transferred MSB
first as shown in Figure 23-26. The SCK phase and polarity follow SPI clock mode 0 (CPOL = 0,
CPHA = 0) where bits are sampled on the rising edge of SCK and output on the falling edge of
SCK. For more detailed timing information see Figure 23-27.
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 23-26. ISP Byte Sequence
SCK
MOSI
7
6
5
4
3
2
1
0
MISO
7
6
5
4
3
2
1
0
Data Sampled
Figure 23-27. Serial Programming Interface Timing
SS
tSCK
tSSE
tSHSL
SCK
tSR
tSSD
tSF
tSLSH
tSOV
tSOE
tSOX
tSOH
MISO
tSIS
tSIH
MOSI
Figure 23-28. Parallel Programming Interface Timing
SS
tSCK
tSSE
tSHSL
SCK
tSR
tSF
tSSD
tSLSH
OE
tPIS
tPIH
tPOE
tPOV
tPOH
tPOX
P0
23.6.6
Timing Parameters
The timing parameters for Figure 23-22, Figure 23-23, Figure 23-24, Figure 23-25, Figure 23-27
and Figure 23-28 are shown in Table .
225
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 23-23. Programming Interface Timing Parameters
Symbol
tCLCL
tPWRUP
tPOR
Note:
226
Parameter
Min
Max
Units
System Clock Cycle Time
0
60
ns
Power On to SS High Time
10
Power-on Reset Time
tPWRDN
SS Tristate to Power Off
tRLZ
RST Low to I/O Tristate
tCLCL
tSTL
RST Low Settling Time
100
tRHZ
RST High to SS Tristate
0
200
µs
100
µs
1
µs
2 tCLCL
ns
ns
2 tCLCL
(1)
ns
tSCK
Serial Clock Cycle Time
ns
tSHSL
Clock High Time
75
ns
tSLSH
Clock Low Time
50
ns
tSR
Rise Time
25
ns
tSF
Fall Time
25
ns
tSIS
Serial Input Setup Time
10
ns
tSIH
Serial Input Hold Time
10
ns
tSOH
Serial Output Hold Time
10
ns
tSOV
Serial Output Valid Time
35
ns
tPIS
Parallel Input Setup Time
10
ns
tPIH
Parallel Input Hold Time
10
ns
tPOH
Parallel Output Hold Time
10
ns
tPOV
Parallel Output Valid Time
35
ns
tSOE
Serial Output Enable Time
10
ns
tSOX
Serial Output Disable Time
25
ns
tPOE
Parallel Output Enable Time
10
ns
tPOX
Parallel Output Disable Time
25
ns
tSSE
SS Active Lead Time
tSLSH
ns
tSSD
SS Inactive Lag Time
tSLSH
ns
tZSS
SCK Setup to SS Low
25
ns
tSSZ
SCK Hold after SS High
25
ns
tWR
Write Cycle Time
2.5
ms
tAWR
Write Cycle with Auto-Erase Time
5
ms
7.5
ms
Chip Erase Cycle Time
tERS
1. tSCK is independent of tCLCL.
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
24. Electrical Characteristics
24.1
Absolute Maximum Ratings*
Operating Temperature ................................... -40°C to +85°C
*NOTICE:
Storage Temperature..................................... -65°C to +150°C
Voltage on Any Pin with Respect to Ground......-0.7V to +5.5V
Maximum Operating Voltage ............................................ 5.5V
DC Output Current...................................................... 15.0 mA
24.2
Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and
functional operation of the device at these or any
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect
device reliability.
DC Characteristics
TA = -40°C to 85°C, VDD = 2.4V to 5.5V (unless otherwise noted)
Symbol
Parameter
VIL
Input Low-voltage
VIH
Input High-voltage
Condition
(1)
VOL
Output Low-voltage
VOH
Output High-voltage
With Weak Pull-ups Enabled
Min
Max
Units
-0.5
0.2 VDD - 0.1
V
0.2 VDD + 0.9
VDD + 0.5
V
0.5
V
IOL = 10 mA, VDD = 2.7V, TA = 85°C
IOH = -80 µA, VDD = 3V  10%
2.4
V
IOH = -30 µA
0.75 VDD
V
IOH = -12 µA
0.9 VDD
V
IOH = -10 mA, TA = 85°C
0.9 VDD
IOH = -5 mA, TA = 85°C
0.75 VDD
VOH1
Output High-voltage
With Strong Pull-ups Enabled
IIL
Logic 0 Input Current
VIN = 0.45V
-50
µA
ITL
Logic 1 to 0 Transition Current
VIN = 2V, VDD = 5V  10%
-750
µA
ILI
Input Leakage Current
0 < VIN < VDD
10
µA
RRST
Reset Pull-up Resistor
150
k
CIO
Pin Capacitance
Test Freq. = 1 MHz, TA = 25°C
10
pF
Active Mode, 12 MHz, VDD = 5.5V
7
mA
Idle Mode, 12 MHz, VDD = 5.5V
P1.0 & P1.1 = 0V or VDD
3
mA
VDD = 5.5V, P1.0 & P1.1 = 0V or VDD
5
µA
VDD = 3V, P1.0 & P1.1 = 0V or VDD
2
µA
Power Supply Current
ICC
Power-down Mode(2)
Notes:
50
1. Under steady state (non-transient) conditions, IOL must be externally limited as follows:
Maximum IOL per port pin: 10 mA
Maximum total IOL for all output pins: 15 mA
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater
than the listed test conditions.
2. Minimum VDD for Power-down is 2V.
3. All characteristics contained in this datasheet are based on simulation and characterization of other microcontrollers manufactured in the same process technology. These values are preliminary values representing design targets, and will be
updated after characterization of actual silicon.
227
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
24.3
Typical Characteristics
The following charts show typical behavior. These figures are not tested during manufacturing.
All current consumption measurements are performed with all I/O pins configured as quasi-bidirectional (with internal pull-ups). A square wave generator with rail-to-rail output is used as an
external clock source for consumption versus frequency measurements.
24.3.1
Supply Current (Internal Oscillator)
Figure 24-1. Active Supply Current vs. Vcc (8.0 MHz Internal Oscillator)
Active Supply Current vs. Vcc
8MHz Internal Oscillator
Icc (mA)
6.5
85C
6.0
-40C
5.5
25C
5.0
4.5
4.0
3.5
2.4
2.7
3.0
3.3
3.6
Vcc (V)
Figure 24-2. Idle Supply Current vs. Vcc (8.0 MHz Internal Oscillator)
Idle Supply Current vs. Vcc
8MHz Internal Oscillator
2.00
85C
-40C
1.75
Icc (mA)
25C
1.50
1.25
1.00
2.4
2.7
3.0
3.3
3.6
Vcc (V)
228
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
24.3.2
Supply Current (External Clock)
Figure 24-3. Active Supply Current vs. Frequency
Active Supply Current vs. Frequency
External Clock Source
20
5.5V
18
5.0V
16
Icc (mA)
14
4.5V
12
3.6V
10
8
3.0V
6
2.4V
4
2
0
0
5
10
15
20
25
Frequency (MHz)
Figure 24-4. Idle Supply Current vs. Frequency
Idle Supply Current vs. Frequency
External Clock Source
7
5.5V
6
5.0V
Icc (mA)
5
4.5V
4
3.6V
3
3.0V
2
2.4V
1
0
0
5
10
15
20
25
Frequency (MHz)
Note:
All characteristics contained in this datasheet are based on simulation and characterization of
other microcontrollers manufactured in the same process technology. These values are preliminary values representing design targets, and will be updated after characterization of actual
silicon.
229
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
24.4
Clock Characteristics
The values shown in this table are valid for TA = -40°C to 85°C and VDD = 2.4 to 5.5V, unless otherwise noted.
Figure 24-5. External Clock Drive Waveform
Table 24-1.
External Clock Parameters
VDD = 2.4V to 5.5V
VDD = 4.5V to 5.5V
Min
Max
Min
Max
Units
20
0
25
MHz
Symbol
Parameter
1/tCLCL
Oscillator Frequency
0
tCLCL
Clock Period
50
tCHCX
40
ns
External Clock High Time
12
ns
tCLCX
External Clock Low Time
12
ns
tCLCH
External Clock Rise Time
5
ns
tCHCL
External Clock Fall Time
5
ns
Min
Max
Units
Low Power Oscillator
0
12
MHz
High Power Oscillator
0
24
MHz
TA = 25°C; VDD = 5.0V
7.92
8.08
MHz
VDD = 2.4 to 5.5V
7.80
8.20
MHz
Table 24-2.
Clock Characteristics
Symbol
Parameter
fXTAL
Crystal Oscillator Frequency
fRC
Internal Oscillator Frequency
230
Condition
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 24-6. Typical Internal Oscillator Frequency vs. VCC
8.10
-40C
8.05
Frequency (MHz)
0C
8.00
25C
7.95
70C
7.90
85C
7.85
7.80
2.4
2.7
3.0
3.3
3.6
Vcc (V)
24.5
Reset Characteristics
The values shown in this table are valid for TA = -40°C to 85°C and VDD = 2.4 to 5.5V, unless otherwise noted.
Table 24-3.
Reset Characteristics
Symbol
Parameter
RRST
Min
Max
Units
Reset Pull-up Resistor
50
150
k
VPOR
Power-On Reset Threshold
1.3
1.6
V
VBOD
Brown-Out Detector Threshold
1.9
2.2
V
VBH
Brown-Out Detector Hysteresis
200
300
mV
tPOR
Power-On Reset Delay
135
150
µs
tWDTRST
Watchdog Reset Pulse Width
24.6
Condition
49tCLCL
ns
External Memory Characteristics
The values shown in this table are valid for TA = -40°C to 85°C and VDD = 2.4 to 5.5V, unless otherwise noted. Under operating conditions, load capacitance for Port 0, ALE and PSEN = 100 pF; load capacitance for all other outputs = 80 pF.
Parameters refer to Figure 24-7, Figure 24-8 and Figure 24-9.
Table 24-4.
External Program and Data Memory Characteristics
Compatibility Mode(1)
Symbol
Parameter
1/tCLCL
Oscillator Frequency
tLHLL
ALE Pulse Width
tAVLL
Fast Mode(1)
Min
Max
Min
Max
Units
0
24
0
24
MHz
tCLCL - d
tCLCL - d(4)
ns
Address Valid to ALE Low
0.5tCLCL - d(2)
0.5tCLCL - d(2)
ns
tLLAX
Address Hold after ALE Low
0.5tCLCL - d(3)
0.5tCLCL - d(3)
ns
tLLIV
ALE Low to Valid Instruction In
tLLPL
ALE Low to PSEN Low
0.5tCLCL - d(2)
0.5tCLCL - d(2)
ns
tPLPH
PSEN Pulse WIdth
1.5tCLCL - d(2)
1.5tCLCL - d(2)
ns
2tCLCL - d
2tCLCL - d
ns
231
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 24-4.
External Program and Data Memory Characteristics
1.5tCLCL - d(2)
1.5tCLCL - d(2)
tPLIV
PSEN Low to Valid Instruction In
tPXIX
Input Instruction Hold after PSEN
tPXIZ
Input Instruction Float after PSEN
tPXAV
PSEN to Address Valid
tAVIV
Address to Valid Instruction In
tPLAZ
PSEN Low to Address Float
tRLRH
RD Pulse Width(5)
3tCLCL - d
tCLCL - d
ns
tWLWH
WR Pulse Width(5)
3tCLCL - d
tCLCL - d
ns
tRLDV
RD Low to Valid Data In
tRHDX
Data Hold after RD
tRHDZ
Data Float after RD
tCLCL - d
tCLCL - d
ns
tLLDV
ALE Low to Valid Data In
4tCLCL - d
2tCLCL - d
ns
tAVDV
Address to Valid Data In
4.5tCLCL - d(2)
2.5tCLCL - d(2)
ns
tLLWL
ALE Low to RD or WR Low
1.5tCLCL - d
tCLCL + d
ns
tAVWL
Address to RD or WR Low
2tCLCL - d(2)
1.5tCLCL - d(2)
ns
tQVWX
Data Valid to WR Transition
1tCLCL - d(2)
0.5tCLCL - d(2)
ns
tQVWH
Data Valid to WR High
4tCLCL - d(2)
1.5tCLCL - d(2)
ns
tWHQX
Data Hold after WR
1tCLCL - d(3)
0.5tCLCL - d(3)
ns
tRLAZ
RD Low to Address Float
tWHAX
Address Hold after RD or WR High
1tCLCL - d(3)
tWHLH
RD or WR High to ALE High
0.5tCLCL - d
Notes:
0
0
ns
0.5tCLCL - d(2)
0.5tCLCL - d(2)
ns
0.5tCLCL - d(2)
0.5tCLCL - d(2)
ns
ns
2.5tCLCL - d(2)
2.5tCLCL - d(2)
ns
10
10
ns
2.5tCLCL - d
0
tCLCL - d
0
1.5tCLCL + d
ns
tCLCL - d
-1tCLCL + d(2)
0.5tCLCL + d
ns
-0.5tCLCL + d(2)
ns
0.5tCLCL - d(3)
ns
tCLCL - d
ns
1. Compatibility Mode timing for MOVX also applies to Fast Mode during exeternal execution of MOVX.
2. This assumes 50% clock duty cycle. The half period depends on the clock high value tCHCX (high duty cycle).
3. This assumes 50% clock duty cycle. The half period depends on the clock low value tCLCX (low duty cycle).
4. In some cases parameter tLHLL may have a minimum of 0.5tCLCL during Fast mode external execution with DISALE = 0.
5. The strobe pulse width may be lengthened by 1, 2 or 3 additional tCLCL using wait states.
Figure 24-7. External Program Memory Read Cycle
tLHLL
ALE
tAVLL
tLLIV
tLLPL
tPLIV
PSEN
tPLAZ
tLLAX
PORT 0
tPLPH
tPXAV
tPXIZ
tPXIX
A0 - A7
INSTR IN
A0 - A7
tAVIV
PORT 2
232
A8 - A15
A8 - A15
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 24-8. External Data Memory Read Cycle
tLHLL
ALE
tLLDV
tLLWL
tWHLH
tRLRH
RD
tRLAZ
tAVLL
PORT 0
tRLDV
tLLAX
tRHDX
DATA IN
A0 - A7
tAVWL
tAVDV
PORT 2
P2
tRHDZ
tWHAX
A8 - A15 FROM DPH OR P2.0 - P2.7
P2
Figure 24-9. External Data Memory Write Cycle
tLHLL
ALE
tLLWL
tWLWH
tWHLH
WR
tQVWX
tAVLL
PORT 0
tWHQX
tLLAX
A0 - A7
DATA OUT
tQVWH
tAVWL
PORT 2
24.7
P2
tWHAX
A8 - A15 FROM DPH OR P2.0 - P2.7
P2
Serial Peripheral Interface Timing
The values shown in these tables are valid for TA = -40°C to 85°C and VDD = 2.4 to 5.5V, unless otherwise noted.
Table 24-5.
SPI Master Characteristics
Symbol
Parameter
Min
tCLCL
Oscillator Period
41.6
ns
tSCK
Serial Clock Cycle Time
4tCLCL
ns
tSHSL
Clock High Time
tSCK/2 - 25
ns
tSLSH
Clock Low Time
tSCK/2 - 25
ns
tSR
Rise Time
25
ns
tSF
Fall Time
25
ns
tSIS
Serial Input Setup Time
10
Max
Units
ns
233
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Table 24-5.
SPI Master Characteristics
Symbol
Parameter
tSIH
Serial Input Hold Time
tSOH
Serial Output Hold Time
10
ns
tSOV
Serial Output Valid Time
35
ns
Max
Units
Table 24-6.
Min
Max
10
Units
ns
SPI Slave Characteristics
Symbol
Parameter
Min
tCLCL
Oscillator Period
41.6
ns
tSCK
Serial Clock Cycle Time
4tCLCL
ns
tSHSL
Clock High Time
1.5 tCLCL - 25
ns
tSLSH
Clock Low Time
1.5 tCLCL - 25
ns
tSR
Rise Time
25
ns
tSF
Fall Time
25
ns
tSIS
Serial Input Setup Time
10
ns
tSIH
Serial Input Hold Time
10
ns
tSOH
Serial Output Hold Time
10
ns
tSOV
Serial Output Valid Time
35
ns
tSOE
Output Enable Time
10
ns
tSOX
Output Disable Time
25
ns
tSSE
Slave Enable Lead Time
10
ns
tSSD
Slave Disable Lag Time
0
ns
Figure 24-10. SPI Master Timing (CPHA = 0)
SS
tSCK
SCK
(CPOL = 0)
SCK
(CPOL = 1)
tSR
tSHSL
tSLSH
tSLSH
tSHSL
tSF
tSIS
tSIH
MISO
tSOH
tSOV
MOSI
234
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Figure 24-11. SPI Slave Timing (CPHA = 0)
SS
tSR
tSCK
tSSE
SCK
(CPOL = 0)
SCK
(CPOL= 1)
tSHSL
tSLSH
tSLSH
tSHSL
tSOV
tSOE
tSSD
tSF
tSOX
tSOH
MISO
tSIS
tSIH
MOSI
Figure 24-12. SPI Master Timing (CPHA = 1)
SS
tSCK
SCK
(CPOL = 0)
SCK
(CPOL = 1)
tSF
tSHSL
tSLSH
tSLSH
tSHSL
tSR
tSIS
tSIH
MISO
tSOV
tSOH
MOSI
Figure 24-13. SPI Slave Timing (CPHA = 1)
SS
tSCK
tSSE
SCK
(CPOL = 0)
SCK
(CPOL = 1)
tSR
tSF
tSHSL
tSLSH
tSLSH
tSHSL
tSOE
tSOV
tSOH
tSSD
tSOX
MISO
tSIS
tSIH
MOSI
235
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
24.8
Two-wire Serial Interface Characteristics
Table 24-7 describes the requirements for devices connected to the Two-wire Serial Bus. The AT89LP51RD2/ED2/ID2
Two-wire Serial Interface meets or exceeds these requirements under the noted conditions. The values shown in this table
are valid for TA = -40°C to 85°C and VDD = 2.4 to 5.5V, unless otherwise noted.
Timing symbols refer to Figure 24-14.
Table 24-7.
Two-wire Serial Bus Requirements
Symbol
Parameter
VIL
VIH
Vhys
(1)
Min
Max
Units
Input Low-voltage
-0.5
0.3 VDD
V
Input High-voltage
0.7 VDD
VDD + 0.5
V
–
V
0
0.4
V
20 + 0.1Cb(3)(2)
300
ns
0.1Cb(3)(2)
250
ns
(2)
ns
Hysteresis of Schmitt Trigger Inputs
VOL(1)
Output Low-voltage
tr(1)
Rise Time for both SDA and SCL
tof(1)
Output Fall Time from VIHmin to VILmax
tSP(1)
Spikes Suppressed by Input Filter
Ii
Input Current each I/O Pin
Ci(1)
Capacitance for each I/O Pin
fSCL
Rp
SCL Clock Frequency
0.05
3 mA sink current
(3)
10 pF < Cb < 400 pF
20 +
Hold Time (repeated) START Condition
tLOW
Low Period of the SCL Clock
tHIGH
High period of the SCL clock
tSU;STA
Set-up time for a repeated START condition
tHD;DAT
Data hold time
tSU;DAT
Data setup time
tSU;STO
Setup time for STOP condition
tBUF
Bus free time between a STOP and START
condition
VDD(2)
0
0.1VDD < Vi < 0.9VDD
50
-10
10
µA
–
10
pF
0
400
kHz
fSCL  100 kHz
V DD – 0.4V
----------------------------3mA
1000ns
------------------Cb

fSCL > 100 kHz
V DD – 0.4V
----------------------------3mA
300ns
---------------Cb

fSCL  100 kHz
4.0
–
µs
fSCL > 100 kHz
0.6
–
µs
fSCL  100 kHz
4.7
–
µs
fSCL > 100 kHz
1.3
–
µs
fSCL  100 kHz
4.0
–
µs
fSCL > 100 kHz
0.6
–
µs
fSCL  100 kHz
4.7
–
µs
fSCL > 100 kHz
0.6
–
µs
fSCL  100 kHz
0
3.45
µs
fSCL > 100 kHz
0
0.9
µs
fSCL  100 kHz
250
–
ns
fSCL > 100 kHz
100
–
ns
fSCL  100 kHz
4.0
–
µs
fSCL > 100 kHz
0.6
–
µs
fSCL  100 kHz
4.7
–
µs
(4)
fCK
> 16fSCL
Value of Pull-up resistor
tHD;STA
Notes:
Condition
1. In AT89LP51RD2/ED2/ID2, this parameter is characterized and not 100% tested.
2. Required only for fSCL > 100 kHz.
236
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
3. Cb = capacitance of one bus line in pF.
4. fCK = CPU clock frequency
Figure 24-14. Two-wire Serial Bus Timing
tHIGH
tof
tr
tLOW
tLOW
SCL
tSU;STA
tHD;STA
tHD;DAT
tSU;DAT
tSU;STO
SDA
tBUF
24.9
Serial Port Timing: Shift Register Mode
The values in this table are valid for VDD = 2.4V to 5.5V and Load Capacitance = 80 pF.
SMOD1 = 0
Min
SMOD1 = 1
Symbol
Parameter
Max
Min
Max
Units
tXLXL
Serial Port Clock Cycle Time
4tCLCL -15
2tCLCL -15
µs
tQVXH
Output Data Setup to Clock Rising Edge
3tCLCL -15
tCLCL -15
ns
tXHQX
Output Data Hold after Clock Rising Edge
tCLCL -15
tCLCL -15
ns
tXHDX
Input Data Hold after Clock Rising Edge
0
0
ns
tXHDV
Input Data Valid to Clock Rising Edge
15
15
ns
Figure 24-15. Shift Register Mode Timing Waveform
SMOD1 = 0
Clock
Write to SBUF
Output Data
0
1
2
3
4
5
6
7
Clear RI
Input Data
Valid
Valid
Valid
Valid
Valid
Valid
Valid
Valid
SMOD1 = 1
Clock
Write to SBUF
Output Data
0
1
2
3
4
5
6
7
Clear RI
Input Data
Valid
Valid
Valid
Valid
Valid
Valid
Valid
Valid
237
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
24.10 Dual Analog Comparator Characteristics
The values shown in this table are valid for TA = -40°C to 85°C and VDD = 2.4 to 5.5V, unless otherwise noted.
Table 24-8.
Dual Analog Comparator Characteristics
Symbol
Parameter
Condition
VCM
Common Mode Input Voltage
VOS
Input Offset Voltage
VAREF
Analog Reference Voltage
VREF
Reference Delta Voltage
tCMP
Comparator Propagation Delay
tAREF
Reference Settling Time
Min
Max
Units
GND
VDD
V
20
mV
1.23
1.36
V
90
120
mV
200
ns
VDD = 3.6V
VIN+ – VIN- = 20mV; VDD = 2.4V
3
µs
Figure 24-16. Analog Reference Voltage Typical Characteristics
1.5
Vref+ 85C
Vref+ 25C
Vref+ -40C
VREF (V)
1.4
Vref 85C
Vref 25C
Vref -40C
1.3
1.2
1.1
2.4
Vref- -40C
Vref- 25C
Vref- 85C
2.7
3.0
3.3
3.6
Vcc (V)
24.11 DADC Characteristics
The values shown in these tables are valid for TA = -40°C to 85°C and VDD = 2.4 to 5.5V, unless otherwise noted.
Table 24-9.
Symbol
ADC Characteristics
Parameter
Condition
Min
Typical
Resolution
238
Max
Units
10
Bits
Absolute Accuracy (including
INL, DNL, quantization error,
gain and offset error)
4
LSB
Integral Non-Linearity (INL)
4
LSB
DIfferential Non-Linearity
(DNL)
4
LSB
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table 24-9.
Symbol
ADC Characteristics (Continued)
Parameter
Condition
Min
Typical
Max
Units
Gain Error
16
LSB
Offset Error
16
LSB
tACK
Clock Period
tADC
Conversion Time
VREF
Reference Voltage
VIN
Single-Ended Input Voltage
VCMI
Differential Input Common
Mode Voltage
VDI
Differential Input Voltage
RIN
Analog Input Resistance
10
k
RMUX
Analog Mux Resistance
10
k
CS/H
Sample & Hold Capacitance
3
pF
Temperature Sensor Gain
2.36
mV/C
Temperature Sensor Offset
0.8
V
Temperature Sensor Linearity
±5
C
VTEMP
500
ns
13tACK
14tACK +
2tCLCL
ns
External Reference
VDD/2 - 0.2
VDD/2
VDD/2 + 0.2
V
Internal Reference
0.9
1.0
1.1
V
VDD/2 - VREF
VDD/2 + VREF
V
GND
VDD
V
0
±VREF
V
.
Table 24-10. DAC Characteristics
Symbol
Parameter
Condition
Min
Typical
Resolution
tACK  tCLCL
Max
Units
10
Bits
tACK
Clock Period
500
ns
tDAC
Conversion Time
VREF
Reference Voltage
VIN
Single-Ended Input Voltage
VCMO
Differential Output
Common Mode Voltage
VDO
Differential Output Voltage
ROUT
Analog Output Resistance
IOH
Output Source Currect
0.3
mA
IOL
Output Sink Current
10
mA
13tACK
14tACK +
2tCLCL
ns
External Reference
VDD/2 - 0.2
VDD/2
VDD/2 + 0.2
V
Internal Reference
0.9
1.0
1.1
V
VDD/2 + VREF
V
VDD/2 + 0.2
V
0
±VREF
V
2
16
k
VDD/2 - VREF
VDD/2 - 0.2
VDD/2
239
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Figure 24-17. Temperature Sensor Channel Characteristic
0.25
0.20
VTEMP - VREF (V)
0.15
0.10
0.05
0.00
5V
-0.05
3V
-0.10
-0.15
-40
-20
0
20
40
60
80
100
Temperature (°C)
Figure 24-18. Temperature Sensor Channel Linearity
6
Linearity Error (°C)
5
4
3
2
5V
1
0
3V
-40
-20
0
20
40
60
80
100
Temperature (°C)
240
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
24.12 Test Conditions
24.12.1
Note:
24.12.2
Note:
24.12.3
AC Testing Input/Output Waveform(1)
1. AC Inputs during testing are driven at VDD - 0.5V for a logic “1” and 0.45V for a logic “0”. Timing measurements are made at
VIH min. for a logic “1” and VIL max. for a logic “0”.
Float Waveform(1)
1. For timing purposes, a port pin is no longer floating when a 100 mV change from load voltage occurs. A port pin begins to
float when 100 mV change from the loaded VOH/VOL level occurs.
ICC Test Condition: Active Mode
Figure 24-19. Connection Diagram for ICC Active Measurement. All Other Pins are
Disconnected
VDD
VDD
ICC
RST
GND
POL
(NC)
XTAL2
CLOCK SIGNAL
VDD
XTAL1
GND
For active supply current measurements all ports are configured in quasi-bidirectional mode.
Timers 0, 1 and 2 are configured to be free running in their default timer modes. The CPU executes a simple random number generator that accesses RAM, the SFR bus and exercises the
ALU and hardware multiplier.
241
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
24.12.4
ICC Test Condition: Idle Mode
Figure 24-20. Connection Diagram for ICC Idle Measurement. All Other Pins are DisconnectedAll Other Pins are Disconnected
VDD
VDD
ICC
RST
GND
POL
(NC)
XTAL2
CLOCK SIGNAL
24.12.5
VDD
XTAL1
GND
Clock Signal Waveform for ICC Tests
Figure 24-21. Clock Signal Waveform for ICC in Active and Idle Modes, tCLCH = tCHCL = 5 ns
VCC - 0.5V
0.45V
0.7 VCC
tCHCX
0.2 VCC - 0.1V
tCHCL
tCLCH
tCHCX
tCLCL
24.12.6
ICC Test Condition: Power-down Mode
Figure 24-22. Connection Diagram for ICC Power-down Measurement.All Other Pins are Disconnected, VDD = 2V to 5.5V
VDD
VDD
ICC
RST
GND
POL
(NC)
XTAL2
VDD
XTAL1
GND
242
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
25. Ordering Information
25.1
Green Package Option (Pb/Halide-free)
Supply Voltage
Speed(1)
Temperature
Range
Data
EEPROM
#
Oscillators
Ordering Code
AT89LP51RD2-20AAU
AT89LP51RD2-20AAUR
AT89LP51RD2-20AU
AT89LP51RD2-20AUR
No
1
AT89LP51RD2-20JU
AT89LP51RD2-20JUR
AT89LP51RD2-20MU
AT89LP51RD2-20MUR
AT89LP51RD2-20PU
AT89LP51ED2-20AAU
AT89LP51ED2-20AAUR
2.4V to 5.5V
20 MHz
Industrial
(-40C to
85C)
AT89LP51ED2-20AU
AT89LP51ED2-20AUR
Yes
1
AT89LP51ED2-20JU
AT89LP51ED2-20JUR
AT89LP51ED2-20MU
AT89LP51ED2-20MUR
AT89LP51ED2-20PU
AT89LP51ID2-20AAU
AT89LP51ID2-20AAUR
AT89LP51ID2-20AU
Yes
2
AT89LP51ID2-20AUR
AT89LP51ID2-20JU
AT89LP51ID2-20JUR
AT89LP51ID2-20MU
Notes:
Package
44AA1 (LQFP)
44A (TQFP)
44J (PLCC)
44M1 (VQFN)
40P6 (PDIP)
44AA1 (LQFP)
44A (TQFP)
44J (PLCC)
44M1 (VQFN)
40P6 (PDIP)
44AA1 (LQFP)
44A (TQFP)
44J (PLCC)
44M1 (VQFN)
Packing
Tray
Reel
Tray
Reel
Stick
Reel
Tray
Reel
Stick
Tray
Reel
Tray
Reel
Stick
Reel
Tray
Reel
Stick
Tray
Reel
Tray
Reel
Stick
Reel
Tray
1. Speed is specified for single-cycle Fast Mode with X2 clock
2. See Table 25-1 on page 244 for a cross reference between AT89C51RD2/ED2/ID2 and AT89LP51RD2/ED2/ID2
Package Types
44AA1
44-lead, Low Profile Plastic Quad Flat Package, 1.4 mm Thickness (LQFP)
44A
44-lead, Thin Plastic Quad Flat Package, 1.0 mm Thickness (TQFP)
44J
44-lead, Plastic J-leaded Chip Carrier (PLCC)
44M1
44-pad, 7 x 7 x 1.0 mm Body, Plastic Very Thin Quad Flat No Lead Package (VQFN/MLF)
40P6
40-lead, 0.600” Wide, Plastic Dual Inline Package (PDIP)
243
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
25.2
Cross Reference with AT89C51RD2/ED2/ID2
Table 25-1.
Ordering Cross Reference when Migrating from AT89C51RD2/ED2/ID2 to AT89LP51RD2/ED2/ID2
Device Migration
Package
Packing
Previous Ordering Code
New Ordering Code
Stick
AT89C51RD2-SLSUM
AT89LP51RD2-20JU
Reel
AT89C51RD2-SLRUM
AT89LP51RD2-20JUR
Tray
AT89C51RD2-RLTUM
AT89LP51RD2-20AAU
Reel
AT89C51RD2-RLRUM
AT89LP51RD2-20AAUR
Stick
AT89C51ED2-SLSUM
AT89LP51ED2-20JU
Reel
AT89C51ED2-SLRUM
AT89LP51ED2-20JUR
Tray
AT89C51ED2-RLTUM
AT89LP51ED2-20AAU
Reel
AT89C51ED2-RLRUM
AT89LP51ED2-20AAUR
Stick
AT89C51ID2-SLSUM
AT89LP51ID2-20JU
Reel
AT89C51ID2-SLRUM
AT89LP51ID2-20JUR
Tray
AT89C51ID2-RLTUM
AT89LP51ID2-20AAU
Reel
AT89C51ID2-RLRUM
AT89LP51ID2-20AAUR
PLCC44
AT89C51RD2 to AT89LP51RD2
VQFP44
PLCC44
AT89C51ED2 to AT89LP51ED2
VQFP44
PLCC44
AT89C51ID2 to AT89LP51ID2
VQFP44
Table 25-2.
Packages Not Found in AT89C51RD2/ED2/ID2
Device
Package
Packing
Ordering Code
PDIP40
Stick
AT89LP51RD2-20PU
Tray
AT89LP51RD2-20AU
Reel
AT89LP51RD2-20AUR
Tray
AT89LP51RD2-20MU
Reel
AT89LP51RD2-20MUR
Stick
AT89LP51ED2-20PU
Tray
AT89LP51ED2-20AU
Reel
AT89LP51ED2-20AUR
Tray
AT89LP51ED2-20MU
Reel
AT89LP51ED2-20MUR
Stick
AT89LP51ID2-20PU
Tray
AT89LP51ID2-20AU
Reel
AT89LP51ID2-20AUR
Tray
AT89LP51ID2-20MU
Reel
AT89LP51ID2-20MUR
TQFP44
AT89C51RD2 to AT89LP51RD2
VQFN44
PDIP40
TQFP44
AT89C51ED2 to AT89LP51ED2
VQFN44
PDIP40
TQFP44
AT89C51ID2 to AT89LP51ID2
VQFN44
244
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
26. Packaging Information
26.1
44AA1 – LQFP
SIDE VIEW
TOP VIEW
d 0.10
SEATING PLANE
Pin 1
b
E1
E
e
12˚(4X)
D1
c
D
12˚(4X)
A
A2
SIDE VIEW
0.25
SEATING PLANE
GAUGE PLANE
A1
d 0.10
BOTTOM VIEW
L
L1
DETAIL A
θ
DETAIL A
COMMON DIMENSIONS
(UNIT OF MEASURE=MM)
NOTE:
1. Refer to JEDEC Drawing MS-026, Variation BCB.
2. Dimension D1 and E1 do not include mold protrusion. Allowable protrusion is 0.25mm
per side. D1 and E1 are maximum plastic body size dimension including mold mismatch.
3. Dimension “b” does not include dambar protrusion. Allowable dambar protrusion shall not
cause the lead width to exceed the maximum b dimension by more then 0.08mm.
SYMBOL
MIN.
NOM.
MAX. NOTE
A
A1
A2
b
C
E
E1
D
D1
e
L
L1
θ
0.05
1.35
0.30
0.09
0.45
0˚
1.40
0.37
12.00
10.00
12.00
10.00
0.80
0.60
1.00
3.5˚
1.60
0.15
1.45
0.45
0.20
0.75
7˚
3
2
2
2/7/11
Package Drawing Contact:
[email protected]
TITLE
GPC
44AA1, 44-lead, 10.0x10.0x1.4mm Body,
0.80mm pitch, (2.00 mm footprint) Low Profile
Plastic Quad Flat Package (LQFP)
AYP
DRAWING NO. REV.
44AA1
A
245
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
26.2
44A – TQFP
D1
D
e
E
E1
b
BOTTOM VIEW
TOP VIEW
C
0°~7°
A1
L
A2
A
SIDE VIEW
COMMON DIMENSIONS
(Unit of Measure = mm)
Notes:
1. This package conforms to JEDEC reference MS-026, Variation ACB.
2. Dimensions D1 and E1 do not include mold protrusion. Allowable
protrusion is 0.25 mm per side. Dimensions D1 and E1 are maximum
plastic body size dimensions including mold mismatch.
3. Lead coplanarity is 0.10 mm maximum.
SYMBOL
MIN
NOM
MAX
A
–
–
1.20
A1
0.05
–
0.15
A2
0.95
1.00
1.05
D
11.75
12.00
12.25
D1
9.90
10.00
10.10
E
11.75
12.00
12.25
E1
9.90
10.00
10.10
B
0.30
–
0.45
C
0.09
–
0.20
L
0.45
–
0.75
e
NOTE
Note 2
Note 2
0.80 TYP
1/10/13
Package Drawing Contact:
[email protected]
246
TITLE
44A, 44-lead 10.0 x 10.0x1.0 mm Body, 0.80 mm
Lead Pitch, Thin Profile Plastic Quad Flat
Package (TQFP)
GPC
DRAWING NO.
REV.
AIX
44A
D
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
26.3
44J – PLCC
1.14(0.045) X 45°
PIN NO. 1
1.14(0.045) X 45°
0.318(0.0125)
0.191(0.0075)
IDENTIFIER
E1
E
D2/E2
B1
B
e
A2
D1
A1
D
A
0.51(0.020)MAX
45° MAX (3X)
COMMON DIMENSIONS
(Unit of Measure = mm)
S MBOL
MIN
NOM
MAX
A
4.191
–
4.572
A1
2.286
–
3.048
A2
0.508
–
–
D
17.399
–
17.653
D1
16.510
–
16.662
E
17.399
Notes:
1.
This package conforms to JEDEC reference MS-018, Variation AC.
E1
16.510
2. Dimensions D1 and E1 do not include mold protrusion.
Allowable protrusion is .010"(0.254 mm) per side. Dimension D1
D2/E2 14.986
and E1 include mold mismatch and are measured at the extreme
B
0.660
material condition at the upper or lower parting line.
B1
0.330
3. Lead coplanarity is 0.004" (0.102 mm) maximum.
–
17.653
–
16.662
–
16.002
–
0.813
–
0.533
e
NOTE
Note 2
Note 2
1.270 TYP
10/04/01
Package Drawing Contact:
[email protected]
TITLE
44J, 44-lead, Plastic J-leaded Chip Carrier (PLCC)
DRAWING NO.
REV.
44J
B
247
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
26.4
44M1 – VQFN/MLF
0.08
D
SEATING PLANE
Marked PIN# 1 ID
E
A
TOP VIEW
A3
A1
SIDE VIEW
L
K
D2
PIN# 1 Corner
COMMON DIMENSIONS
Option A
1
2
3
E2
Option B
K
b
PIN# 1
Chamfer
(C0.30)
e
Option C
BOTTOM VIEW
(UNIT OF MEASURE=MM)
PIN# 1
Triangle
PIN# 1
Notch
(0.20 R)
SYMBOL
MIN
NOM
MAX
A
0.80
0.90
1.00
A1
-
0.02
0.05
A3
NOTE
0.20 REF
b
0.18
0.23
0.30
D
6.90
7.00
7.10
D2
5.00
5.20
5.40
E
6.90
7.00
7.10
E2
5.00
5.20
5.40
e
0.50 BSC
L
0.59
0.64
0.69
K
0.20
0.26
0.41
10/19/09
Package Drawing Contact:
[email protected]
248
TITLE
44M1, 44-pad, 7 x 7 x 1.0 mm Body, Lead
Pitch 0.50 mm, 5.20 mm Exposed Pad, Thermally
Enhanced Plastic Very Thin Quad Flat No
Lead Package (VQFN)
GPC
ZWS
DRAWING NO. REV.
44M1
I
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
26.5
40P6 – PDIP
40
21
E1
1
20
D
e
A2 A
BASE
PLANE
-CSEATING
PLANE
A1
L
b2
.015
b j
0.10 m C
E
GAGE
PLANE
See
Lead Detail
Z Z
COMMON DIMENSIONS
(UNIT OF MEASURE=MM)
C
L
eC
Lead Detail
eA
eB
Notes:
1. This package conforms to JEDEC reference MS-011,
Variation AC.
2. Dimensions D and E1 do not include mold Flash or
Protrusion. Mold Flash or Protrusion shall not exceed
0.25 mm (0.010").
c
Symbol
A
A1
A2
Min.
0.39
3.18
Nom.
-
Max.
6.35
4.95
Note
b
b2
0.356
0.77
-
0.558
1.77
c
D
E
0.204
50.3
15.24
-
0.381
53.2
15.87
Note 2
E1
12.32
-
14.73
Note 2
L
2.93
-
5.08
e
eA
eB
-
2.54 BSC
15.24 BSC
-
17.78
eC
0.000
-
1.524
11/28/11
Package Drawing Contact:
[email protected]
TITLE
40P6, 40-lead, 0.600”/15.24 mm Wide Plastic Dual
Inline Package (PDIP)
GPC
DRAWING NO.
REV.
PBL
40P6
C
249
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
27. Revision History
Revision No.
History
Revision A – July 2011

Initial Release.






Updated LQFP44 Drawing (Section 26.1 on page 245).
Cosmetic changes to “Register Summary” on page 28.
Added “Register Index” on page 32.
Added mention of bootloader vector under Reset (page 58).
Updated DAC timing (page 171 and Figure 20-4).
Updated DAC output resistance (Figure 20-5 on page 172 and
Table 24-10 on page 239).
Fixed error in Temperature sensor channel selection (Table 20-3
on page 175).
Added temperature sensor characteristics to Table 24-9 on page
238.
Added temperature sensor characteristic graphs Figure 24-17 and
Figure 24-18 on page 240.
Updated table, DADI – DADC Input Control Register, ACS2-0
values.
Updated table, User Configuration Fuse Definitions, Note 1.
Updated table, API Call Summary, returned values for Erase
Block, Program Data Byte, Program SSB, and Program Data Page
to none.
Updated package drawings 44A, 44M1, 40P6, and 44AA to
44AA1.
Updated datasheet status from preliminary to complete.


Revision B – February 2013






250
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
Table of Contents
Features ..................................................................................................... 1
1
2
3
4
5
Pin Configurations ................................................................................... 2
1.1
44-lead TQFP/LQFP ..........................................................................................2
1.2
44-lead PLCC ....................................................................................................2
1.3
44-pad VQFN/MLF ............................................................................................3
1.4
40-pin PDIP .......................................................................................................3
1.5
Pin Description ..................................................................................................4
Overview ................................................................................................... 6
2.1
Block Diagram ...................................................................................................8
2.2
System Configuration ........................................................................................8
2.3
Comparison to the Atmel AT89C51RD2/ED2/ID2 ...........................................10
Memory Organization ............................................................................ 13
3.1
Program Memory .............................................................................................13
3.2
Internal Data Memory ......................................................................................16
3.3
External Data Memory .....................................................................................17
3.4
Extra RAM (EDATA) ........................................................................................22
3.5
EEPROM .........................................................................................................22
3.6
Extended Stack ...............................................................................................26
Special Function Registers ................................................................... 27
4.1
Register Summary ...........................................................................................28
4.2
Register Index .................................................................................................32
Enhanced CPU ....................................................................................... 35
5.1
Fast Mode ........................................................................................................35
5.2
Compatibility Mode ..........................................................................................36
5.3
Multiply–Accumulate Unit (MAC) .....................................................................36
5.4
Enhanced Dual Data Pointers .........................................................................39
5.5
Instruction Set Extensions ...............................................................................43
i
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
6
7
8
9
System Clock ......................................................................................... 45
6.1
Crystal Oscillator A ..........................................................................................46
6.2
External Clock Source A ..................................................................................47
6.3
Internal RC Oscillator ......................................................................................47
6.4
Crystal Oscillator B (AT89LP51ID2) ................................................................47
6.5
External Clock Source B (AT89LP51ID2) ........................................................48
6.6
Dual Oscillator Support (AT89LP51ID2) ..........................................................48
6.7
X1/X2 Feature .................................................................................................50
6.8
System Clock Prescaler ..................................................................................51
6.9
Peripheral Clocks ............................................................................................52
6.10
Timer Subclock (AT89L51ID2) ........................................................................54
Reset ....................................................................................................... 55
7.1
Power-on Reset ...............................................................................................55
7.2
Brown-out Reset ..............................................................................................56
7.3
External Reset .................................................................................................57
7.4
Hardware Watchdog Reset .............................................................................58
7.5
PCA Watchdog Reset ......................................................................................58
7.6
Software Reset ................................................................................................58
7.7
Bootloader Vector ............................................................................................58
Power Saving Modes ............................................................................. 59
8.1
Idle Mode .........................................................................................................59
8.2
Power-down Mode ...........................................................................................60
8.3
Reducing Power Consumption ........................................................................61
8.4
Low Power Configuration ................................................................................62
Interrupts ................................................................................................ 63
9.1
Interrupt Priority ...............................................................................................63
9.2
Interrupt Response ..........................................................................................65
9.3
Interrupt Registers ...........................................................................................67
10 External Interrupts ................................................................................. 70
ii
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
11 Keyboard Interface and General-purpose Interrupts .......................... 70
11.1
Registers .........................................................................................................72
11.2
Port Configuration ............................................................................................73
11.3
Port Analog Functions .....................................................................................76
11.4
Port Read-Modify-Write ...................................................................................77
11.5
Port Alternate Functions ..................................................................................77
12 Enhanced Timer 0 and Timer 1 with PWM ........................................... 81
12.1
Registers .........................................................................................................82
12.2
Mode 0 – Variable Width Timer/Counter .........................................................84
12.3
Mode 1 – 16-bit Auto-Reload Timer/Counter ...................................................85
12.4
Mode 2 – 8-bit Auto-Reload Timer/Counter .....................................................86
12.5
Mode 3 – 8-bit Split Timer ...............................................................................86
12.6
Pulse Width Modulation ...................................................................................87
13 Timer 2 .................................................................................................... 91
13.1
Timer 2 Registers ............................................................................................93
13.2
Capture Mode ..................................................................................................94
13.3
Auto-Reload Mode ...........................................................................................95
13.4
Baud Rate Generator ......................................................................................97
13.5
Frequency Generator (Programmable Clock Out) ...........................................98
14 Programmable Counter Array (PCA) .................................................... 99
14.1
PCA Timer/Counter .........................................................................................99
14.2
PCA Modules .................................................................................................102
14.3
PCA Capture Mode .......................................................................................105
14.4
16-bit Software Timer/ Compare Mode .........................................................105
14.5
High Speed Output Mode ..............................................................................106
14.6
Pulse Width Modulator Mode ........................................................................107
14.7
PCA Watchdog Timer ....................................................................................108
15 Hardware Watchdog Timer .................................................................. 108
15.1
Software Reset ..............................................................................................109
15.2
WDT Registers ..............................................................................................110
iii
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
16 Serial Interface (UART) ........................................................................ 111
16.1
Multiprocessor Communications ...................................................................113
16.2
Baud Rates ....................................................................................................113
16.3
Framing Error Detection ................................................................................118
16.4
Automatic Address Recognition ....................................................................118
16.5
More About Mode 0 .......................................................................................120
16.6
More About Mode 1 .......................................................................................124
16.7
More About Modes 2 and 3 ...........................................................................126
17 Enhanced Serial Peripheral Interface ................................................. 129
17.1
Interface Description ......................................................................................130
17.2
Master Operation ...........................................................................................133
17.3
Slave Operation .............................................................................................133
17.4
Error Conditions .............................................................................................134
17.5
Serial Clock Timing ........................................................................................135
17.6
Registers .......................................................................................................136
18 Two-Wire Serial Interface .................................................................... 138
18.1
Data Transfer and Frame Format ..................................................................139
18.2
Multi-master Bus Systems, Arbitration and Synchronization .........................141
18.3
Overview of the TWI Module .........................................................................143
18.4
Register Overview .........................................................................................145
18.5
Using the TWI ................................................................................................146
18.6
Transmission Modes .....................................................................................148
19 Dual Analog Comparators ................................................................... 161
19.1
Analog Input Muxes .......................................................................................162
19.2
Internal Reference Voltage ............................................................................163
19.3
Comparator Interrupt Debouncing .................................................................163
20 Digital-to-Analog/Analog-to-Digital Converter .................................. 168
iv
20.1
ADC Operation ..............................................................................................170
20.2
Temperature Sensor ......................................................................................171
20.3
DAC Operation ..............................................................................................171
20.4
Clock Selection ..............................................................................................172
20.5
Starting a Conversion ....................................................................................173
20.6
Noise Considerations ....................................................................................173
20.7
Registers .......................................................................................................174
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
AT89LP51RD2/ED2/ID2
21 Instruction Set Summary ..................................................................... 177
21.1
Instruction Set Extensions .............................................................................181
22 On-Chip Debug System ....................................................................... 187
22.1
Physical Interface ..........................................................................................187
22.2
Software Breakpoints ....................................................................................188
22.3
Limitations of On-Chip Debug .......................................................................188
23 Flash Memory Programming ............................................................... 189
23.1
Memory Organization ....................................................................................190
23.2
User Configuration Fuses ..............................................................................192
23.3
Flash Hardware Security ...............................................................................193
23.4
In-Application Programming (IAP) .................................................................194
23.5
Bootloader .....................................................................................................202
23.6
In-System Programming (ISP) .......................................................................217
24 Electrical Characteristics .................................................................... 227
24.1
Absolute Maximum Ratings* .........................................................................227
24.2
DC Characteristics .........................................................................................227
24.3
Typical Characteristics ..................................................................................228
24.4
Clock Characteristics .....................................................................................230
24.5
Reset Characteristics ....................................................................................231
24.6
External Memory Characteristics ...................................................................231
24.7
Serial Peripheral Interface Timing .................................................................233
24.8
Two-wire Serial Interface Characteristics ......................................................236
24.9
Serial Port Timing: Shift Register Mode ........................................................237
24.10
Dual Analog Comparator Characteristics ......................................................238
24.11
DADC Characteristics ....................................................................................238
24.12
Test Conditions ..............................................................................................241
25 Ordering Information ........................................................................... 243
25.1
Green Package Option (Pb/Halide-free) ........................................................243
25.2
Cross Reference with AT89C51RD2/ED2/ID2 ..............................................244
v
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
26 Packaging Information ........................................................................ 245
26.1
44AA1 – LQFP ..............................................................................................245
26.2
44A – TQFP ...................................................................................................246
26.3
44J – PLCC ...................................................................................................247
26.4
44M1 – VQFN/MLF .......................................................................................248
26.5
40P6 – PDIP ..................................................................................................249
27 Revision History ................................................................................... 250
Table of Contents....................................................................................... i
vi
AT89LP51RD2/ED2/ID2
Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Atmel Corporation
1600 Technology Drive, San Jose, CA 95110 USA
T: (+1)(408) 441.0311
F: (+1)(408) 487.2600
|
www.atmel.com
© 2013 Atmel Corporation. All rights reserved. / Rev.: Atmel-3714B-Microcontroller-8051-AT89LP51RD2-ED2-ID2-Datasheet-022013
Atmel®, Atmel logo and combinations thereof, Enabling Unlimited Possibilities®, and others are registered trademarks or trademarks of Atmel Corporation or its
subsidiaries. Other terms and product names may be trademarks of others.
Disclaimer: The information in this document is provided in connection with Atmel products. No license, express or implied, by estoppel or otherwise, to any intellectual property right is
granted by this document or in connection with the sale of Atmel products. EXCEPT AS SET FORTH IN THE ATMEL TERMS AND CONDITIONS OF SALES LOCATED ON THE ATMEL
WEBSITE, ATMEL ASSUMES NO LIABILITY WHATSOEVER AND DISCLAIMS ANY EXPRESS, IMPLIED OR STATUTORY WARRANTY RELATING TO ITS PRODUCTS INCLUDING,
BUT NOT LIMITED TO, THE IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT. IN NO EVENT SHALL ATMEL BE
LIABLE FOR ANY DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE, SPECIAL OR INCIDENTAL DAMAGES (INCLUDING, WITHOUT LIMITATION, DAMAGES FOR LOSS AND
PROFITS, BUSINESS INTERRUPTION, OR LOSS OF INFORMATION) ARISING OUT OF THE USE OR INABILITY TO USE THIS DOCUMENT, EVEN IF ATMEL HAS BEEN ADVISED
OF THE POSSIBILITY OF SUCH DAMAGES. Atmel makes no representations or warranties with respect to the accuracy or completeness of the contents of this document and reserves
the right to make changes to specifications and products descriptions at any time without notice. Atmel does not make any commitment to update the information contained herein.
Unless specifically provided otherwise, Atmel products are not suitable for, and shall not be used in, automotive applications. Atmel products are not intended, authorized, or warranted
for use as components in applications intended to support or sustain life.