ATMEL AT89C51RE2

Features
• 80C52 Compatible
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
– 8051 Instruction Compatible
– Four 8-bit I/O Ports (44 Pins Version)
– Three 16-bit Timer/Counters
– 256 bytes Scratch Pad RAM
– 11 Interrupt Sources With 4 Priority Levels
ISP (In-System Programming) Using Standard VCC Power Supply
Integrated Power Monitor (POR/PFD) to Supervise Internal Power Supply
Boot ROM Contains Serial Loader for In-System Programming
High-speed Architecture
– In Standard Mode:
40 MHz (Vcc 2.7V to 5.5V, Both Internal and External Code Execution)
60 MHz (Vcc 4.5V to 5.5V and Internal Code Execution Only)
– In X2 Mode (6 Clocks/Machine Cycle)
20 MHz (Vcc 2.7V to 5.5V, Both Internal and External Code Execution)
30 MHz (Vcc 4.5V to 5.5V and Internal Code Execution Only)
128K bytes On-chip Flash Program/Data Memory
– 128 bytes Page Write with auto-erase
– 100k Write Cycles
On-chip 8192 bytes Expanded RAM (XRAM)
– Software Selectable Size (0, 256, 512, 768, 1024, 1792, 2048, 4096, 8192 bytes)
Dual Data Pointer
Extended stack pointer to 512 bytes
Variable Length MOVX for Slow RAM/Peripherals
Improved X2 Mode with Independant Selection for CPU and Each Peripheral
Keyboard Interrupt Interface on Port 1
SPI Interface (Master/Slave Mode)
8-bit Clock Prescaler
Programmable Counter Array with:
– High Speed Output
– Compare/Capture
– Pulse Width Modulator
– Watchdog Timer Capabilities
Asynchronous Port Reset
Two Full Duplex Enhanced UART with Dedicated Internal Baud Rate Generator
Low EMI (inhibit ALE)
Hardware Watchdog Timer (One-time Enabled with Reset-Out), Power-Off Flag
Power Control Modes: Idle Mode, Power-down Mode
Power Supply: 2.7V to 5.5V
Temperature Ranges: Industrial (-40 to +85°C)
Packages: PLCC44, VQFP44
8-bit Flash
Microcontroller
AT89C51RE2
Description
AT89C51RE2 is a high performance CMOS Flash version of the 80C51 CMOS single chip 8-bit
microcontroller. It contains a 128 Kbytes Flash memory block for program.
The 128 Kbytes Flash memory can be programmed either in parallel mode or in serial mode with
the ISP capability or with software. The programming voltage is internally generated from the
standard VCC pin.
The AT89C51RE2 retains all features of the Atmel 80C52 with 256 bytes of internal RAM, a 10source 4-level interrupt controller and three timer/counters.
In addition, the AT89C51RE2 has a Programmable Counter Array, an XRAM of 8192 bytes, a
Hardware Watchdog Timer, SPI and Keyboard, two serial channels that facilitates multiprocessor communication (EUART), a speed improvement mechanism (X2 mode) and an extended
stack mode that allows the stack to be extended in the lower 256 bytes of XRAM.
The fully static design of the AT89C51RE2 allows to reduce system power consumption by
bringing the clock frequency down to any value, even DC, without loss of data.
The AT89C51RE2 has 2 software-selectable modes of reduced activity and 8-bit clock prescaler
for further reduction in power consumption. In the Idle mode the CPU is frozen while the peripherals and the interrupt system are still operating. In the power-down mode the RAM is saved and
all other functions are inoperative.
The added features of the AT89C51RE2 make it more powerful for applications that need pulse
width modulation, high speed I/O and counting capabilities such as alarms, motor control,
corded phones, smart card readers.
Table 1. Memory Size and I/O pins
AT89C51RE2
PLCC44
VQFP44
2
Flash (bytes)
XRAM (bytes)
TOTAL RAM (bytes)
I/O
128K
8192
8192 + 256
34
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Block Diagram
(2) (2)
(1)
(1) (1)
XTALA1
EUART
XTALA2
Flash
128Kx8
RAM
256x8
XRAM
8192 x 8
C51
CORE
TxD_1
RxD_1
Keyboard
(1)
(1)
(3) (3)
Watch
Dog
Timer2 Keyboard
POR
PFD
PCA
XTALB1(1)
XTALB2
T2
T2EX
PCA
ECI
Vss
VCC
TxD_0
RxD_0
Figure 1. Block Diagram
EUART_1
IB-bus
CPU
ALE/ PROG
PSEN
EA
Timer 0
Timer 1
(2)
INT
Ctrl
External Bus
TWI
SPI
BOOT Regulator
4K x8 POR / PFD
ROM
SDA
SCL
MISO
MOSI
SCK
SS
P5
P4
P3
P2
P1
(1) (1) (1)(1)
P0
INT1
(2) (2)
T1
(2) (2)
INT0
Port 0 Port 1Port 2 Port 3 Port4 Port 5
RESET
WR
Parallel I/O Ports &
(2)
T0
RD
(1): Alternate function of Port 1
(2): Alternate function of Port 3
(3): Alternate function of Port 6
3
7663E–8051–10/08
P0.2/AD2
P0.3/AD3
P0.1/AD1
P0.0/AD0
VCC
Rx_OCD
P1.0/T2
P1.1/T2EX/SS
P1.2/ECI
P1.3/CEX0
P1.4/CEX1
Pin Configurations
6 5 4 3 2 1 44 43 42 41 40
P1.5/CEX2/MISO
39
38
P0.4/AD4
P1.6/CEX3/SCK
7
8
P1.7/CEx4/MOSI
9
37
P0.6/AD6
RST
10
36
P0.7/AD7
P3.0/RxD_0
11
12
13
35
34
EA
33
ALE
14
15
32
31
PSEN
16
30
P2.6/A14
17
29
P2.5/A13
P6.0/RxD_1/SDA
P3.1/TxD_0
P3.2/INT0
P3.3/INT1
P3.4/T0
P3.5/T1
AT89C51RE2
PLCC44
P0.5/AD5
P6.1/TxD_1/SCL
P2.7/A15
P0.3/AD3
P0.2/AD2
P0.1/AD1
P0.0/AD0
VCC
Rx_OCD
P1.0/T2/XTALB1
P1.1/T2EX/SS
P1.2/ECI
P1.3/CEX0
P1.4/CEX1
P2.3/A11
P2.4/A12
P2.2/A10
P2.1/A9
Tx_OCD
P2.0/A8
VSS
XTAL1
P3.7/RD
XTAL2
P3.6/WR
18 19 20 21 22 23 24 25 26 27 28
44 43 42 41 40 39 38 37 36 35 34
P1.5/CEX2/MISO
1
P1.6/CEX3/SCK
P1.7/CEX4/MOSI
2
33
32
P0.4/AD4
31
P0.6/AD6
30
P0.7/AD7
29
28
EA
27
ALE
PSEN
P0.5/AD5
RST
3
4
P3.0/RxD_0
5
AT89C51RE2
P6.0/RxD_1/SDA
6
VQFP44
P3.1/TxD_0
P3.2/INT0
7
8
P3.3/INT1
9
26
25
10
24
P2.6/A14
11
23
P2.5/A13
P3.4/T0
P3.5/T1
P6.1/TxD_1/SCL
P2.7/A15
4
P2.3/A11
P2.4/A12
P2.2/A10
P2.1/A9
Tx_OCD
P2.0/A8
VSS
XTAL1
XTAL2
P3.7/RD
P3.6/WR
12 13 14 15 16 17 18 19 20 21 22
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 2. Pin Description
Pin Number
Mnemonic
LCC
VQFP 1.4
Type
22
16
I
Ground: 0V reference
39
I
Optional Ground: Contact the Sales Office for ground connection.
44
38
I
Power Supply: This is the power supply voltage for normal, idle and power-down operation
P0.0-P0.7
43-36
37-30
I/O
Port 0: Port 0 is an open-drain, bidirectional I/O port. Port 0 pins that have 1s written to them
float and can be used as high impedance inputs. Port 0 must be polarized to VCC or VSS in
order to prevent any parasitic current consumption. Port 0 is also the multiplexed low-order
address and data bus during access to external program and data memory. In this
application, it uses strong internal pull-up when emitting 1s. Port 0 also inputs the code bytes
during EPROM programming. External pull-ups are required during program verification
during which P0 outputs the code bytes.
P1.0-P1.7
2-9
40-44
1-3
I/O
Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. Port 1 pins that have 1s
written to them are pulled high by the internal pull-ups and can be used as inputs. As inputs,
Port 1 pins that are externally pulled low will source current because of the internal pull-ups.
Port 1 also receives the low-order address byte during memory programming and
verification.
VSS
Vss1
VCC
Name and Function
Alternate functions for TSC8x54/58 Port 1 include:
P2.0-P2.7
2
40
I/O
T2 (P1.0): Timer/Counter 2 external count input/Clockout
3
41
I
T2EX (P1.1): Timer/Counter 2 Reload/Capture/Direction Control
4
42
I
ECI (P1.2): External Clock for the PCA
5
43
I/O
CEX0 (P1.3): Capture/Compare External I/O for PCA module 0
6
44
I/O
CEX1 (P1.4): Capture/Compare External I/O for PCA module 1
7
1
I/O
CEX2 (P1.5): Capture/Compare External I/O for PCA module 2
8
2
I/O
CEX3 (P1.6): Capture/Compare External I/O for PCA module 3
9
3
I/O
CEX4 (P1.7): Capture/Compare External I/O for PCA module 4
24-31
18-25
I/O
Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. Port 2 pins that have 1s
written to them are pulled high by the internal pull-ups and can be used as inputs. As inputs,
Port 2 pins that are externally pulled low will source current because of the internal pull-ups.
Port 2 emits the high-order address byte during fetches from external program memory and
during accesses to external data memory that use 16-bit addresses (MOVX @DPTR).In this
application, it uses strong internal pull-ups emitting 1s. During accesses to external data
memory that use 8-bit addresses (MOVX @Ri), port 2 emits the contents of the P2 SFR.
Some Port 2 pins receive the high order address bits during EPROM programming and
verification:
P2.0 to P2.5 for RB devices
P2.0 to P2.6 for RC devices
P2.0 to P2.7 for RD devices.
P3.0-P3.7
11,
13-19
5,
7-13
I/O
Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. Port 3 pins that have 1s
written to them are pulled high by the internal pull-ups and can be used as inputs. As inputs,
Port 3 pins that are externally pulled low will source current because of the internal pull-ups.
Port 3 also serves the special features of the 80C51 family, as listed below.
11
5
I
RXD_0 (P3.0): Serial input port
13
7
O
TXD_0 (P3.1): Serial output port
14
8
I
INT0 (P3.2): External interrupt 0
5
7663E–8051–10/08
Pin Number
Mnemonic
P6.0-P6.1
LCC
VQFP 1.4
Type
Name and Function
15
9
I
INT1 (P3.3): External interrupt 1
16
10
I
T0 (P3.4): Timer 0 external input
17
11
I
T1 (P3.5): Timer 1 external input
18
12
O
WR (P3.6): External data memory write strobe
19
13
O
RD (P3.7): External data memory read strobe
Port 6: Port 6 is an 2-bit bidirectional I/O port with internal pull-ups. Port 6 pins that have 1s
written to them are pulled high by the internal pull-ups and can be used as inputs. As inputs,
Port 6 pins that are externally pulled low will source current because of the internal pull-ups.
Port 6 also serves some special features as listed below.
12,34
6, 28
12
6
I
12
6
I/O
34
28
O
RXD_1 (P6.0): Serial input port
SDA (P6.0) : TWI Serial Data
SDA is the bidirectional TWI data line.
TXD_1 (P6.1) : Serial output port
SCL ( P6.1) : TWI Serial Clock
34
28
I/O
SCL output the serial clock to slave peripherals.
SCL input the serial clock from master.
Reset
10
4
I/O
Reset: A high on this pin for two machine cycles while the oscillator is running, resets the
device. An internal diffused resistor to VSS permits a power-on reset using only an external
capacitor to VCC. This pin is an output when the hardware watchdog forces a system reset.
ALE/PROG
33
27
O (I)
Address Latch Enable/Program Pulse: Output pulse for latching the low byte of the
address during an access to external memory. In normal operation, ALE is emitted at a
constant rate of 1/6 (1/3 in X2 mode) the oscillator frequency, and can be used for external
timing or clocking. Note that one ALE pulse is skipped during each access to external data
memory. This pin is also the program pulse input (PROG) during Flash programming. ALE
can be disabled by setting SFR’s AUXR.0 bit. With this bit set, ALE will be inactive during
internal fetches.
PSEN
32
26
O
Program Store ENable: The read strobe to external program memory. When executing
code from the external program memory, PSEN is activated twice each machine cycle,
except that two PSEN activations are skipped during each access to external data memory.
PSEN is not activated during fetches from internal program memory.
EA
35
29
I
External Access Enable: EA must be externally held low to enable the device to fetch code
from external program memory locations 0000H to FFFFH (RD). If security level 1 is
programmed, EA will be internally latched on Reset.
XTAL1
21
15
I
XTAL2
20
14
O
Crystal 2: Output from the inverting oscillator amplifier
Tx_OCD
23
17
O
Tx_OCD: On chip debug Serial output port
Rx_OCD
1
39
I
Rx_OCD: On chip debug Serial input port
6
Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock generator
circuits.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
SFR Mapping
The Special Function Registers (SFRs) of the AT89C51RE2 fall into the following categories:
•
C51 core registers: ACC, B, DPH, DPL, PSW, SP
•
I/O port registers: P0, P1, P2, P3, P4, P5, P6
•
Timer registers: T2CON, T2MOD, TCON, TH0, TH1, TH2, TMOD, TL0, TL1, TL2, RCAP2L,
RCAP2H
•
Serial I/O port registers: SADDR_0, SADEN_0, SBUF_0, SCON_0, SADDR_1, SADEN_1,
SBUF_1, SCON_1,
•
PCA (Programmable Counter Array) registers: CCON, CCAPMx, CL, CH, CCAPxH,
CCAPxL (x: 0 to 4)
•
Power and clock control registers: PCON, CKAL, CKCON0_1
•
Hardware Watchdog Timer registers: WDTRST, WDTPRG
•
Interrupt system registers: IE0, IPL0, IPH0, IE1, IPL1, IPH1
•
Keyboard Interface registers: KBE, KBF, KBLS
•
2-wire Interface registers: SSCON, SSCS, SSDAT, SSADR
•
SPI registers: SPCON, SPSTR, SPDAT
•
BRG (Baud Rate Generator) registers: BRL_0, BRL_1, BDRCON_0, BDRCON_1
•
Memory register: FCON, FSTA
•
Clock Prescaler register: CKRL
•
Others: AUXR, AUXR1, CKCON0, CKCON1, BMSEL
7
7663E–8051–10/08
Table 3. C51 Core SFRs
Mnemonic
Add
Name
ACC
E0h
Accumulator
B
F0h
B Register
PSW
D0h
Program Status Word
SP
81h
Stack Pointer
DPL
82h
Data Pointer Low byte
DPH
83h
Data Pointer High byte
7
6
5
4
3
2
1
0
CY
AC
F0
RS1
RS0
OV
F1
P
7
6
5
4
3
2
1
0
SMOD1_0
SMOD0_0
-
POF
GF1
GF0
PD
IDL
Table 4. System Management SFRs
Mnemonic
Add
Name
PCON
87h
Power Control
AUXR
8Eh
Auxiliary Register 0
-
-
M0
XRS2
XRS1
XRS0
EXTRA
M
AO
AUXR1
A2h
Auxiliary Register 1
EES
SP9
U2
-
GF2
0
-
DPS
CKRL
97h
Clock Reload Register
-
-
-
-
-
-
-
-
BMSEL
92h
Bank Memory Select
MBO2
MBO1
MBO0
-
FBS2
FBS1
FBS0
CKCON0
8Fh
Clock Control Register 0
TWIX2
WDX2
PCAX2
SIX2_0
T2X2
T1X2
T0X2
X2
CKCON1
AFh
Clock Control Register 1
-
-
-
-
-
-
SIX2_1
SPIX2
Table 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
-
-
-
-
ES_1
ESPI
ETWI
EKBD
IPH0
B7h
Interrupt Priority Control High 0
-
PPCH
PT2H
PSH
PT1H
PX1H
PT0H
PX0H
IPL0
B8h
Interrupt Priority Control Low 0
-
PPCL
PT2L
PSL
PT1L
PX1L
PT0L
PX0L
IPH1
B3h
Interrupt Priority Control High 1
-
-
-
-
PSH_1
SPIH
IE2CH
KBDH
IPL1
B2h
Interrupt Priority Control Low 1
-
-
-
-
PSL_1
SPIL
IE2CL
KBDL
7
6
5
4
3
2
1
0
Table 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
8
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 6. Port SFRs
Mnemonic
Add
Name
P5
E8h
8-bit Port 5
P6
F8h
2-bit Port 5
7
6
5
4
3
2
1
0
-
-
-
-
-
-
7
6
5
4
3
2
1
0
FPL2
FPL1
FPL0
FPS
FMOD2
FMOD1
FMOD0
FSE
FLOAD
FBUSY
Table 7. Flash and EEPROM Data Memory SFR
Mnemonic
Add
Name
FCON
D1h
Flash Controller Control
FPL3
FSTA
D3h
Flash Controller Status
FMR
Table 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
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
WDTRST
A6h
WatchDog Timer Reset
WDTPRG
A7h
WatchDog Timer Program
-
-
-
-
-
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
Table 9. PCA SFRs
Mnemo
-nic
Add Name
7
6
5
4
3
2
1
0
CCON
D8h
PCA Timer/Counter Control
CF
CR
-
CCF4
CCF3
CCF2
CCF1
CCF0
CMOD
D9h
PCA Timer/Counter Mode
CIDL
WDTE
-
-
-
CPS1
CPS0
ECF
CL
E9h
PCA Timer/Counter Low byte
9
7663E–8051–10/08
Table 9. PCA SFRs (Continued)
Mnemo
-nic
Add Name
CH
F9h
7
6
5
4
3
2
1
0
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
ECOM2
CAPP2
CAPN2
MAT2
TOG2
PWM2
ECCF2
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
PCA Timer/Counter High byte
CCAPM2 DCh PCA Timer/Counter Mode 2
-
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
Table 10. Serial I/O Port SFRs
Mnemonic
Add
Name
SCON_0
98h
Serial Control 0
SBUF_0
99h
Serial Data Buffer 0
SADEN_0
B9h
Slave Address Mask 0
SADDR_0
A9h
Slave Address 0
BDRCON_0
9Bh
Baud Rate Control 0
BRL_0
9Ah
Baud Rate Reload 0
SCON_1
C0h
Serial Control 1
SBUF_1
C1h
Serial Data Buffer 1
SADEN_1
BAh
Slave Address Mask 1
SADDR_1
AAh
Slave Address 1
BDRCON_1
BCh
Baud Rate Control 1
BRL_1
BBh
Baud Rate Reload 1
10
7
6
5
4
3
2
1
0
FE/SM0_0
SM1_0
SM2_0
REN_0
TB8_0
RB8_0
TI_0
RI_0
BRR_0
TBCK_0
RBCK_0
SPD_0
SRC_0
REN_1
TB8_1
RB8_1
TI_1
RI_1
BRR_1
TBCK_1
RBCK_1
SPD_1
SRC_1
FE_1/SM0_1
SM1_1
SMOD1_1
SMOD0_1
SM2_1
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 11. SPI Controller SFRs
Mnemonic
Add
Name
7
6
5
4
3
2
1
0
SPCON
C3h
SPI Control
SPR2
SPEN
SSDIS
MSTR
CPOL
CPHA
SPR1
SPR0
SPSCR
C4h
SPI Status
SPIF
OVR
MODF
SPTE
UARTM
SPTEIE
MODFIE
SPDAT
C5h
SPI Data
SPD7
SPD6
SPD5
SPD4
SPD3
SPD2
SPD1
SPD0
7
6
5
4
3
2
1
0
Table 12. Two-Wire Interface 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
SSD7
SSD6
SSD5
SSD4
SSD3
SSD2
SSD1
SSD0
SSADR
96h
Synchronous Serial Address
SSA7
SSA6
SSA5
SSA4
SSA3
SSA2
SSA1
SSGC
7
6
5
4
3
2
1
0
Table 13. Keyboard Interface SFRs
Mnemonic
Add
Name
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
11
7663E–8051–10/08
Table below shows all SFRs with their address and their reset value.
Table 14. SFR Mapping
Bit
Non Bit addressable
addressable
0/8
F8h
F0h
E8h
E0h
1/9
2/A
3/B
4/C
5/D
6/E
P6
CH
CCAP0H
CCAP1H
CCAP2H
CCAP3H
CCAP4H
XXXX XX11
0000 0000
XXXX XXXX
XXXX XXXX
XXXX XXXX
XXXX XXXX
XXXX XXXX
F7h
P5
CL
CCAP0L
CCAP1L
CCAP2L
CCAP3L
CCAP4L
1111 1111
0000 0000
XXXX XXXX
XXXX XXXX
XXXX XXXX
XXXX XXXX
XXXX XXXX
E7h
CMOD
CCAPM0
CCAPM1
CCAPM2
CCAPM3
CCAPM4
00XX X000
X000 0000
X000 0000
X000 0000
X000 0000
X000 0000
D0h
PSW
0000 0000
0000 0000
C8h
T2CON
0000 0000
T2MOD
XXXX XX00
B8h
B0h
A8h
A0h
98h
90h
88h
80h
FCON
DFh
FSTA
xxxx x000
RCAP2L
0000 0000
RCAP2H
0000 0000
D7h
TL2
0000 0000
TH2
0000 0000
CFh
SCON_1
0000 0000
SBUF_1
SPCON
SPSCR
SPDAT
P4
0000 0000
0001 0100
0000 0000
XXXX XXXX
C0h
U2(AUXR1.5)
=1
EFh
ACC
0000 0000
CCON
U2(AUXR1.5)
=0
FFh
B
0000 0000
00X0 0000
D8h
7/F
C7h
1111 1111
IPL0
SADEN_0
SADEN1
BRL_1
BDRCON_1
X000 000
0000 0000
0000 0000
0000 0000
XXX0 0000
BFh
P3
IEN1
IPL1
IPH1
IPH0
1111 1111
XXXX 0000
XXXX 0000
XXXX 0111
X000 0000
IEN0
SADDR_0
SADDR_1
CKCON1
0000 0000
0000 0000
0000 0000
XXXX XX00
P2
AUXR1
WDTRST
WDTPRG
1111 1111
000x 11x0
XXXX XXXX
XXXX X000
SCON_0
SBUF_0
BRL_0
BDRCON_0
KBLS
KBE
KBF
0000 0000
XXXX XXXX
0000 0000
XXX0 0000
0000 0000
0000 0000
0000 0000
P1
BMSEL
SSCON
SSCS
SSDAT
SSADR
CKRL
0000 0YYY
0000 0000
1111 1000
1111 1111
1111 1110
1111 1111
AUXR
XX00 1000
0000 0000
TCON
TMOD
TL0
TL1
TH0
TH1
0000 0000
0000 0000
0000 0000
0000 0000
0000 0000
P0
1111 1111
SP
0000 0111
DPL
0000 0000
DPH
0000 0000
0/8
1/9
2/A
3/B
CKCON0
PCON
00X1 0000
4/C
5/D
6/E
AFh
A7h
9Fh
1111 1111
0000 0000
B7h
97h
8Fh
87h
7/F
Reserved
12
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Enhanced
Features
X2 Feature
In comparison to the original 80C52, the AT89C51RE2 implements some new features, which
are:
•
X2 option
•
Dual Data Pointer
•
Extended RAM
•
Extended stack
•
Programmable Counter Array (PCA)
•
Hardware Watchdog
•
SPI interface
•
4-level interrupt priority system
•
power-off flag
•
ONCE mode
•
ALE disabling
•
Enhanced features on the UART and the timer 2
The AT89C51RE2 core needs only 6 clock periods per machine cycle. This feature called ‘X2’
provides the following advantages:
•
Divide frequency crystals by 2 (cheaper crystals) while keeping same CPU power.
•
Save power consumption while keeping same CPU power (oscillator power saving).
•
Save power consumption by dividing dynamically the operating frequency by 2 in operating
and idle modes.
•
Increase CPU power by 2 while keeping same crystal frequency.
In order to keep the original C51 compatibility, a divider by 2 is inserted between the XTAL1 signal and the main clock input of the core (phase generator). This divider may be disabled by
software.
Description
The clock for the whole circuit and peripherals is first divided by two before being used by the
CPU core and the peripherals.
This allows any cyclic ratio to be accepted on XTAL1 input. In X2 mode, as this divider is
bypassed, the signals on XTAL1 must have a cyclic ratio between 40 to 60%.
Figure 2 shows the clock generation block diagram. X2 bit is validated on the rising edge of the
XTAL1÷2 to avoid glitches when switching from X2 to STD mode. Figure 3 shows the switching
mode waveforms.
Figure 2. Clock Generation Diagram
CKRL
2
XTAL1
FXTAL
FOSC
XTAL1:2
0
1
8 bit Prescaler
FCLK CPU
FCLK PERIPH
X2
CKCON0
13
7663E–8051–10/08
Figure 3. Mode Switching Waveforms
XTAL1
XTAL1:2
X2 bit
FOSC
CPU clock
STD Mode
X2 Mode
STD Mode
The X2 bit in the CKCON0 register (see Table 15) allows a switch from 12 clock periods per
instruction to 6 clock periods and vice versa. At reset, the speed is set according to X2 bit of the
Fuse Configuration Byte (FCB). By default, Standard mode is active. Setting the X2 bit activates
the X2 feature (X2 mode).
The T0X2, T1X2, T2X2, UartX2, PcaX2, and WdX2 bits in the CKCON0 register (See Table 15.)
and SPIX2 bit in the CKCON1 register (see Table 16) allows a switch from standard peripheral
speed (12 clock periods per peripheral clock cycle) to fast peripheral speed (6 clock periods per
peripheral clock cycle). These bits are active only in X2 mode.
14
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 15. CKCON0 Register
CKCON0 - Clock Control Register (8Fh)
7
6
5
4
3
2
1
0
TWIX2
WDX2
PCAX2
SIX2_0
T2X2
T1X2
T0X2
X2
Bit
Bit
Number
Mnemonic
Description
2-wire cloTBck
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
7
TWIX2
effect)
Cleared to select 6 clock periods per peripheral clock cycle.
Set to select 12 clock periods per peripheral clock cycle.
Watchdog Clock
6
WDX2
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect).
Cleared to select 6 clock periods per peripheral clock cycle.
Set to select 12 clock periods per peripheral clock cycle.
Programmable Counter Array Clock
5
PCAX2
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect).
Cleared to select 6 clock periods per peripheral clock cycle. Set to select 12 clock
periods per peripheral clock cycle.
Enhanced UART0 Clock (Mode 0 and 2)
4
SIX2_0
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect).
Cleared to select 6 clock periods per peripheral clock cycle. Set to select 12 clock
periods per peripheral clock cycle.
Timer2 Clock
3
T2X2
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect).
Cleared to select 6 clock periods per peripheral clock cycle.
Set to select 12 clock periods per peripheral clock cycle.
Timer1 Clock
2
T1X2
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect).
Cleared to select 6 clock periods per peripheral clock cycle. Set to select 12 clock
periods per peripheral clock cycle.
Timer0 Clock
1
T0X2
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect).
Cleared to select 6 clock periods per peripheral clock cycle. Set to select 12 clock
periods per peripheral clock cycle.
CPU Clock
0
X2
Cleared to select 12 clock periods per machine cycle (STD mode) for CPU and all the
peripherals. Set to select 6clock periods per machine cycle (X2 mode) and to enable the
individual peripherals’X2’ bits. Programmed by hardware after Power-up regarding
Hardware Security Byte (HSB), Default setting, X2 is cleared.
Reset Value = X000 000’HSB. X2’b (See “Fuse Configuration Byte: FCB”)
Not bit addressable
15
7663E–8051–10/08
16
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 16. CKCON1 Register
CKCON1 - Clock Control Register (AFh)
7
6
5
4
3
2
1
0
-
-
-
-
-
-
SIX2_1
SPIX2
Bit
Bit
Number
Mnemonic
7
-
Reserved
6
-
Reserved
5
-
Reserved
4
-
Reserved
3
-
Reserved
2
-
Reserved
Description
Enhanced UART1 Clock (Mode 0 and 2)
1
0
SIX2_1
SPIX2
(This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit has no
effect).
Cleared to select 6 clock periods per peripheral clock cycle. Set to select 12 clock
periods per peripheral clock cycle.
SPI (This control bit is validated when the CPU clock X2 is set; when X2 is low, this bit
has no effect).
Clear to select 6 clock periods per peripheral clock cycle.
Set to select 12 clock periods per peripheral clock cycle.
Reset Value = XXXX XX00b
Not bit addressable
17
7663E–8051–10/08
Dual Data
Pointer Register
DPTR
The additional data pointer can be used to speed up code execution and reduce code size.
The dual DPTR structure is a way by which the chip will specify the address of an external data
memory location. There are two 16-bit DPTR registers that address the external memory, and a
single bit called DPS = AUXR1.0 (see Table 17) that allows the program code to switch between
them (Refer to Figure 4).
Figure 4. Use of Dual Pointer
External Data Memory
7
0
DPS
AUXR1(A2H)
DPTR1
DPTR0
DPH(83H) DPL(82H)
18
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 17. AUXR1 register
AUXR1- Auxiliary Register 1(0A2h)
7
6
5
4
3
2
1
0
EES
SP9
U2
-
GF2
0
-
DPS
Bit
Bit
Number
Mnemonic
7
EES
Description
Enable Extended Stack
This bit allows the selection of the stack extended mode.
Set to enable the extended stack
Clear to disable the extended stack (default value)
6
SP9
Stack Pointer 9th Bit
This bit has no effect when the EES bit is cleared.
Set when the stack pointer belongs to the XRAM memory space
Cleared when the stack pointer belongs to the 256bytes of internal RAM.
P4 bit addressable
5
U2
Clear to map SCON_1 register at C0h sfr address
Set to map P4 port register at C0h address.
4
-
3
GF2
2
0
1
-
0
DPS
Reserved
The value read from this bit is indeterminate. Do not set this bit.
This bit is a general purpose user flag. *
Always cleared.
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Data Pointer Selection
Cleared to select DPTR0.
Set to select DPTR1.
Reset Value: XX0X XX0X0b
Not bit addressable
Note:
*Bit 2 stuck at 0; this allows to use INC AUXR1 to toggle DPS without changing GF3.
ASSEMBLY LANGUAGE
; Block move using dual data pointers
; Modifies DPTR0, DPTR1, A and PSW
; note: DPS exits opposite of entry state
; unless an extra INC AUXR1 is added
;
00A2 AUXR1 EQU 0A2H
;
0000 909000MOV DPTR,#SOURCE ; address of SOURCE
0003 05A2 INC AUXR1 ; switch data pointers
0005 90A000 MOV DPTR,#DEST ; address of DEST
0008 LOOP:
0008 05A2 INC AUXR1 ; switch data pointers
000A E0 MOVX A,@DPTR ; get a byte from SOURCE
000B A3 INC DPTR ; increment SOURCE address
000C 05A2 INC AUXR1 ; switch data pointers
000E F0 MOVX @DPTR,A ; write the byte to DEST
000F A3 INC DPTR ; increment DEST address
19
7663E–8051–10/08
0010 70F6JNZ LOOP ; check for 0 terminator
0012 05A2 INC AUXR1 ; (optional) restore DPS
INC is a short (2 bytes) and fast (12 clocks) way to manipulate the DPS bit in the AUXR1 SFR.
However, note that the INC instruction does not directly force the DPS bit to a particular state,
but simply toggles it. In simple routines, such as the block move example, only the fact that DPS
is toggled in the proper sequence matters, not its actual value. In other words, the block move
routine works the same whether DPS is '0' or '1' on entry. Observe that without the last instruction (INC AUXR1), the routine will exit with DPS in the opposite state.
20
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Memory Architecture
AT89C51RE2 features several on-chip memories:
•
Flash memory:
containing 128 Kbytes of program memory (user space) organized into 128 bytes pages.
•
Boot ROM:
4K bytes for boot loader.
•
8K bytes internal XRAM
Physical memory
organisation
Figure 5. Physical memory organisation
Fuse Configuration Byte(1 byte)
FCB
Hardware Security (1 byte)
HSB
Column Latches (128 bytes)
1FFFFh
128K bytes
Flash memory
user space
4K bytes
ROM
RM0
FM0
8K bytes
XRAM
00000h
256 bytes
IRAM
21
7663E–8051–10/08
Expanded RAM
(XRAM)
The AT89C51RE2 provides additional Bytes of random access memory (RAM) space for
increased data parameter handling and high level language usage.
AT89C51RE2 devices have expanded RAM in external data space configurable up to 8192bytes
(see Table 18.).
The AT89C51RE2 has internal data memory that is mapped into four separate segments.
The four segments are:
1. The Lower 128 bytes of RAM (addresses 00h to 7Fh) are directly and indirectly
addressable.
2. The Upper 128 bytes of RAM (addresses 80h to FFh) are indirectly addressable only.
3. The Special Function Registers, SFRs, (addresses 80h to FFh) are directly addressable
only.
4. The expanded RAM bytes are indirectly accessed by MOVX instructions, and with the
EXTRAM bit cleared in the AUXR register (see Table 18).
The lower 128 bytes can be accessed by either direct or indirect addressing. The Upper 128
bytes can be accessed by indirect addressing only. The Upper 128 bytes occupy the same
address space as the SFR. That means they have the same address, but are physically separate from SFR space.
Figure 6. Internal and External Data Memory Address
0FFh to 1FFFh
0FFh
Upper
128 bytes
Internal
Ram
indirect accesses
XRAM
0FFFFh
0FFh
80h
Special
Function
Register
direct accesses
External
Data
Memory
80h
7Fh
Lower
128 bytes
Internal
Ram
direct or indirect
accesses
00
00
00FFh up to 1FFFh
0000
When an instruction accesses an internal location above address 7Fh, the CPU knows whether
the access is to the upper 128 bytes of data RAM or to SFR space by the addressing mode used
in the instruction.
22
•
Instructions that use direct addressing access SFR space. For example: MOV 0A0H, # data,
accesses the SFR at location 0A0h (which is P2).
•
Instructions that use indirect addressing access the Upper 128 bytes of data RAM. For
example: MOV @R0, # data where R0 contains 0A0h, accesses the data byte at address
0A0h, rather than P2 (whose address is 0A0h).
•
The XRAM bytes can be accessed by indirect addressing, with EXTRAM bit cleared and
MOVX instructions. This part of memory which is physically located on-chip, logically
occupies the first bytes of external data memory. The bits XRS0 and XRS1 are used to hide
a part of the available XRAM as explained in Table 18. This can be useful if external
peripherals are mapped at addresses already used by the internal XRAM.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
•
With EXTRAM = 0, the XRAM is indirectly addressed, using the MOVX instruction in
combination with any of the registers R0, R1 of the selected bank or DPTR. An access to
XRAM will not affect ports P0, P2, P3.6 (WR) and P3.7 (RD). For example, with EXTRAM =
0, MOVX @R0, # data where R0 contains 0A0H, accesses the XRAM at address 0A0H
rather than external memory. An access to external data memory locations higher than the
accessible size of the XRAM will be performed with the MOVX DPTR instructions in the
same way as in the standard 80C51, with P0 and P2 as data/address busses, and P3.6 and
P3.7 as write and read timing signals. Accesses to XRAM above 0FFH can only be done by
the use of DPTR.
•
With EXTRAM = 1, MOVX @Ri and MOVX @DPTR will be similar to the standard
80C51.MOVX @ Ri will provide an eight-bit address multiplexed with data on Port0 and any
output port pins can be used to output higher order address bits. This is to provide the
external paging capability. MOVX @DPTR will generate a sixteen-bit address. Port2 outputs
the high-order eight address bits (the contents of DPH) while Port0 multiplexes the low-order
eight address bits (DPL) with data. MOVX @ Ri and MOVX @DPTR will generate either
read or write signals on P3.6 (WR) and P3.7 (RD).
The stack pointer (SP) may be located anywhere in the 256 bytes RAM (lower and upper RAM)
internal data memory. The stack may be located in the 256 lower bytes of the XRAM by activating the extended stack mode (see EES bit in AUXR1).
The M0 bit allows to stretch the XRAM timings; if M0 is set, the read and write pulses are
extended from 6 to 30 clock periods. This is useful to access external slow peripherals.
23
7663E–8051–10/08
Registers
Table 18. AUXR Register
AUXR - Auxiliary Register (8Eh)
7
6
5
4
3
2
1
0
-
-
M0
XRS2
XRS1
XRS0
EXTRAM
AO
Bit
Bit
Number
Mnemonic
7
-
6
-
Description
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Pulse length
5
M0
Cleared to stretch MOVX control: the RD/ and the WR/ pulse length is 6 clock periods
(default).
Set to stretch MOVX control: the RD/ and the WR/ pulse length is 30 clock periods.
XRAM Size
4-2
XRS2:0
XRS2 XRS1 XRS0
0
0
0
XRAM size
256 bytes
0
0
1
512 bytes
0
1
0
768 bytes
0
1
1
1024 bytes
1
0
0
1792 bytes
1
0
1
2048 bytes
1
1
0
4096 bytes
1
1
1
8192 bytes (default)
EXTRAM bit
Cleared to access internal XRAM using movx @ Ri/ @ DPTR.
1
EXTRAM
Set to access external memory.
Programmed by hardware after Power-up regarding Hardware Security Byte (HSB),
default setting, XRAM selected.
0
AO
ALE Output bit
Cleared, ALE is emitted at a constant rate of 1/6 the oscillator frequency (or 1/3 if X2
mode is used). (default) Set, ALE is active only during a MOVX or MOVC instruction is
used.
Reset Value = XX01 1100b
Not bit addressable
24
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Extended Stack
The lowest bytes of the XRAM may be used to allow extension of the stack pointer.
The extended stack allows to extend the standard C51 stack over the 256 bytes of internal RAM.
When the extended stack mode is activated (EES bit in AUXR1), the stack pointer (SP) can
grow in the lower 256 bytes of the XRAM area.
The stack extension consists in a 9 bits stack pointer where the ninth bit is located in SP9 (bit 6
of AUXR1). The SP9 then indicates if the stack pointer belongs to the internal RAM (SP9
cleared) or to the XRAM memory (SP9 set).
To ensure backward compatibility with standard C51 architecture, the extended mode is disable
at chip reset.
Figure 7. Stack modes
Logical MCU
Address
Logical MCU
Address
SP Value
FFFFh
SP Value
FFFFh
XRAM
XRAM
00FFh
FFh
SP9=1
0000h
00h
0000h
FFh
FFh
256 bytes
IRAM
00h
00h
FFh
FFh
256 bytes
IRAM
256 SP values
rollover within 256B of IRAM
SP9=0
00h
00h
Standard C51 Stack mode EES = 0
512 SP Values
rollover in:
256B of IRAM
+
lower 256B of XRAM
Extended Stack mode Stack EES = 1
Figure 8. AUXR1 register
AUXR1- Auxiliary Register 1(0A2h)
7
6
5
4
3
2
1
0
EES
SP9
U2
-
GF2
0
-
DPS
Bit
Bit
Number
Mnemonic
7
EES
Description
Enable Extended Stack
This bit allows the selection of the stack extended mode.
Set to enable the extended stack
Clear to disable the extended stack (default value)
25
7663E–8051–10/08
Bit
Bit
Number
Mnemonic
Description
Stack Pointer 9th Bit
This bit has no effect when the EES bit is cleared.
6
SP9
Set when the stack pointer belongs to the XRAM memory space
Cleared when the stack pointer belongs to the 256bytes of internal RAM. Set and
cleared by hardware. Can only be read.
P4 bit addressable
5
U2
Clear to map SCON_1 register at C0h sfr address
Set to map P4 port register at C0h address.
4
-
3
GF2
2
0
1
-
0
DPS
Reserved
The value read from this bit is indeterminate. Do not set this bit.
This bit is a general purpose user flag. *
Always cleared.
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Data Pointer Selection
Cleared to select DPTR0.
Set to select DPTR1.
Reset Value = 00XX 00X0b
Not bit addressable
26
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Flash Memory
General
Description
The Flash memory increases EPROM and ROM functionality with in-circuit electrical erasure
and programming. It contains 128K bytes of program memory organized in 1024 pages of 128
bytes. This memory is both parallel and serial In-System Programmable (ISP). ISP allows
devices to alter their own program memory in the actual end product under software control. A
default serial loader (bootloader) program allows ISP of the Flash.
The programming does not require external high programming voltage. The necessary high programming voltage is generated on-chip using the standard VCC pins of the microcontroller.
Features
Flash memory
organization
•
Flash 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 Flash allows programming via the serial port without the need of a
user provided loader.
•
Up to 64K byte external program memory if the internal program memory is disabled (EA =
0).
•
Programming and erase voltage with standard 5V or 3V VCC supply.
AT89C51RE2 features several on-chip memories:
•
Flash memory FM0:
containing 128 Kbytes of program memory (user space) organized into 128 bytes pages.
•
Boot ROM RM0:
4K bytes for boot loader.
•
8K bytes internal XRAM
27
7663E–8051–10/08
Physical memory
organisation
Figure 9. Physical memory organisation
Fuse Configuration Byte(1 byte)
FCB
Hardware Security (1 byte)
HSB
Extra Row FM0 (128 bytes)
Column Latches (128 bytes)
4K bytes
ROM
1FFFFh
RM0
128K bytes
Flash memory
user space
FM0
00000h
On-Chip Flash
memory
The AT89C51RE2 implements up to 128K bytes of on-chip program/code memory. Figure 9 and
Figure 10 shows the partitioning of internal and external program/code memory spaces according to EA value.
The memory partitioning of the 8051 core microcontroller is typical a Harvard architecture where
program and data areas are held in separate memory areas. The program and data memory
areas use the same physical address range from 0000H-FFFFH and a 8 bit instruction
code/data format.
To access more than 64kBytes of code memory, without modifications of the MCU core, and
development tools, the bank switching method is used.
The internal program memory is expanded to 128kByte in the ´Expanded Configuration’, the
data memory remains in the ´Normal Configuration´. The program memory is split into four 32
kByte banks (named Bank 0-2). The MCU core still addresses up to 64kBytes where the upper
32Kbytes can be selected between 3 32K bytes bank of on-chip flash memory. The lower 32K
bank is used as common area for interrupt subroutines, bank switching and functions calls
between banks.
The AT89C51RE2 also implements an extra upper 32K bank (Bank3) that allows external code
execution.
28
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Figure 10. Program/Code Memory Organization EA=1
Logical MCU
Address
Physical Flash
Address
Logical MCU
Address
Physical Flash
Address
Logical MCU
Address
Physical Flash
Address
Logical MCU
Address
FFFFh
0FFFFh
FFFFh
17FFFh
FFFFh
1FFFFh
FFFFh
upper 32K
Bank 0
upper 32K
Bank 1
8000h
08000h
7FFFh
07FFFh
8000h
upper 32K
Bank 3
Optional
External
Memory
upper 32K
Bank 2
10000h
8000h
18000h
8000h
32K
Common
On-Chip flash code memory
0000h
00000h
External code memory
29
7663E–8051–10/08
When EA=0, the on-chip flash memory is disabled and the MCU core can address only up to
64kByte of external memory (none of the on-chip flash memory FM0 banks or RM0 can be
mapped and executed).
Figure 11. Program/Code Memory Organization EA=0
Logical MCU
Address
FFFFh
External Physical Memory
Address
0FFFFh
64K
Common
On-Chip flash code memory
0000h
30
00000h
External code memory
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
On-Chip ROM
bootloader
The On-chip ROM bootloader (RM0) is enable only for ISP operations after reset (bootloader
execution). The RM0 memory area belongs to a logical addressable memory space called ‘Bank
Boot’.
RM0 cannot be activated from the On-chip flash memory. It means that it is not possible activate the Bank Boot area by software (it prevents any RM0 execution and flash corruption from
the user application).
RM0 logical area consists in an independent code execution memory area of 4K bytes starting
at logical 0x0000 address (it allows the use of the interrupts in the bootloader execution).
Logical MCU
Address
Physical
Address
Logical MCU
Address
Physical
Address
Logical MCU
Address
Physical
Address
Logical MCU
Address
FFFFh
0FFFFh
FFFFh
17FFFh
FFFFh
1FFFFh
FFFFh
Bank 0
Bank 1
8000h
08000h
7FFFh
07FFFh
8000h
Bank 2
10000h
8000h
Bank 3
(Ext)
18000h
8000h
Logical MCU
Address
On-Chip ROM memory (RM0)
1000h
On-Chip flash code memory
External code memory
0000h
00000h
0000h
ROM
Address
1000h
Bank
BOOT
0000h
31
7663E–8051–10/08
Boot process
The BRV2-0 bits of the FCB (see Table 20 on page 34), the EA pin value upon reset and the
presence of the external hardware conditions, allow to modify the default reset vector of the
AT89C51RE2.
The Hardware conditions (EA = 1, PSEN = 0) during the Reset falling edge force 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 ISP operation. The hardware conditions
allows to force the enter in ISP mode whatever the configurations bits.
Figure 12. Boot Reset vector configuration
EA pin
Hardware conditions
BRV2-0
MCU reset vector
0
X
X
External Code at address 0x0000
YES
X
RM0 at address 0x0000 (ATMEL Bootloader)
111
FM0 at address 0x0000 with bank0 mapped
110
FM0 at address 0xFFFC in Bank 0
101
FM0 at address 0xFFFC in Bank 1
100
FM0 at address 0xFFFC in Bank 2
011
RM0 at address 0x0000 (ATMEL Bootloader)
1
NO
010
001
Reserved
(FM0 at address 0x0000 with bank 0 mapped)
000
32
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
FM0 Memory
Architecture
The FM0 flash memory is made up of 5 blocks:
1. The memory array (user space) 128K bytes
2. The Extra Row also called FM0 XAF
3. The Hardware security bits (HSB)
4. The Fuse Configuration Byte (FCB)
5. The column latch
User Space
This space is composed of a 128K bytes Flash memory organized in 1024 pages of 128 bytes. It
contains the user’s application code. This block can be access in Read/write mode from FM0
and boot memory area. (When access in write mode from FM0, the CPU core enter pseudo idle
mode).
Extra Row (XRow or
XAF)
This row is a part of FM0 and has a size of 128 bytes. The extra row (XAF) may contain information for boot loader usage.This block can be access in Read/write mode from FM0 and boot
memory area. (When access in write mode from FM0, the CPU core enter pseudo idle mode).
Hardware security Byte
(HSB)
The Hardware security Byte is a part of FM0 and has a size of 1 byte.
The 8 bits can be read/written by software (from FM0 or RM0) and written by hardware in parallel mode.
The HSB bits can be written to ‘0’ without any restriction (increase the security level of the chip),
but can be written to ‘1’ only when the corresponding memory area of the lock bits was full chip
erased.
Table 19. Hardware Security Byte (HSB)
7
6
5
4
3
2
1
0
-
-
-
-
-
FLB2
FLB1
FLB0
Bit
Number
Bit
Mnemonic
7
-
Unused
6-4
-
Reserved
3
-
Unused
2-0
FLB2-0
Description
FM0 Memory Lock Bits
See Table 32 on page 52
33
7663E–8051–10/08
Fuse Configuration Byte
(FCB)
The Fuse configuration byte is a part of FM0.
The 8 bits read/written by software (from FM0 or RM0) and written by hardware in parallel mode.
Table 20. Fuse Configuration Byte (FCB)
7
6
5
4
3
2
1
0
X2
-
-
-
-
BRV2
BRV1
BRV0
Bit
Number
Bit
Mnemonic
7
X2
Description
X2 Mode
Programmed (‘0’ value) to force X2 mode (6 clocks per instruction) after reset
Unprogrammed (‘1’ value) to force X1 mode, Standard Mode, after reset (Default)
6-3
-
Unused
Boot Reset Vector
These bits allow to configure the reset vector of the product according to the following
values:
1 1 1: Reset at address 0x0000 of FM0 with Bank0 mapped
1 1 0: Reset at address 0xFFFC of Bank 0
2-0
BRV2-0-
1 0 1: Reset at address 0xFFFC of Bank 1
1 0 0: Reset at address 0xFFFC of Bank 2
0 1 1: Reset at address 0x0000 of RM0 (Internal ROM bootloader execution)
0 1 0: Reserved for further extension but same as 1 1 1
0 0 1: Reserved for further extension but same as 1 1 1
0 0 0: Reserved for further extension but same as 1 1 1
34
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Column latches
The column latches, also part of FM0, has a size of one page (128 bytes).
The column latches are the entrance buffers of the three previous memory locations (user array,
XROW, Hardware security byte and Fuse Configuration Byte).
This block is write only from FM0, RM0.
Cross Memory Access
Description overview
The FM0 memory can be programmed from RM0 without entering idle mode.
Programming FM0 from FM0 makes the CPU core entering “pseudo idle” mode.
In the pseudo idle mode, the code execution is halted, the peripherals are still running (like standard idle mode) but all interrupt are delayed to the end of this mode. There are fours ways of
exiting pseudo idle mode:
•
At the end of the regular flash programming operation
•
Reset the chip by external reset
•
Reset the chip by hardware watchdog
•
Reset the chip by PCA watchdog
Programming FM0 from external memory code (EA=0 or EA=1,with Bank3 active) is impossible.
If a reset occurs during flash programming the target page could be incompletely erased or programmed, but any other memory location (FM0, RAM, XRAM) remain unchanged.
The Table 21 shows all software flash access allowed.
Table 21. Cross Memory Access
Code executing from
FM0
(user Flash)
RM0
(boot ROM)
External memory
EA = 0
or
EA=1, Bank3
1.
FM0
(user Flash)
RM0
(boot ROM)
Read
ok
Denied
Load column latch
ok
N.A.
Write
ok (pseudo idle mode)
N.A.
Read
ok
ok
Load column latch
ok
N.A.
Write
ok
N.A.
Read
(1)
Denied
Load column latch
Denied
N.A.
Write
Denied
N.A.
Action
Depends of general lock bits configuration
N.A. Not applicable
35
7663E–8051–10/08
Access and
Operations
Descriptions
FM0 FLASH Registers
The CPU interfaces to the flash memory through the FCON register, AUXR1 register and FSTA
register.
These registers are used to map the columns latch, HSB, FCB and extra row in the working data
or code space.
BMSEL Register
Table 22. BMSEL Register
BMSEL Register (S:92h)
Bank Memory Select
7
6
5
MBO2
MBO1
MBO0
Bit Number
Bit
Mnemonic
Description
4
3
2
1
0
FBS2
FBS1
FBS0
Memory Bank Operation
These bits select the target memory bank for flash write or read operation. These bits
allows to read or write the on-chip flash memory from one upper 32K bytes to another
one.
7-5
MBO2:0
0 X X: The on-chip flash operation target banked is the same as FBS2:0
1 0 0: The target memory bank is forced to Bank0
1 0 1: The target memory bank is forced to Bank1
1 1 0: The target memory bank is forced to Bank2
1 1 1: The target memory bank is forced to Bank3 (optional External bank)
4-3
Reserved
Fetch Bank Selection
These bits select the upper 32K bytes execution bank:
FBS1:0 can be read/write by software.
FBS2 is read-only by software (the Boot bank can not be mapped from FM0)
2-0
FBS2:0
0 0 0 Bank0
0 0 1 Bank1
0 1 0 Bank2
0 1 1 Bank3 (optionnal external bank)
1 X X Boot Bank (Read only)
Upon reset FBS2:0 is initialized according to BRV2:0 configuration bits in FCB.
Reset Value= 0000 0YYYb (where YYY depends on BRV2:0 value in Fuse Configuration Byte)
36
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
FCON Register
Table 23. FCON Register
FCON Register (S:D1h)
Flash Control Register
7
6
5
4
3
2
1
0
FPL3
FPL2
FPL1
FPL0
FPS
FMOD2
FMOD1
FMOD0
Bit Number
Bit
Mnemonic
Description
7-4
FPL3:0
Programming Launch Command Bits
Write 5Xh followed by AXh to launch the programming according to FMOD2:0. (see
Table 26.)
Flash Map Program Space
When this bit is set:
3
FPS
The MOVX @DPTR, A instruction writes in the columns latches space
When this bit is cleared:
The MOVX @DPTR, A instruction writes in the regular XDATA memory space
2-0
FMOD2:0
Flash Mode
These bits allow to select the target memory area and operation on FM0
See Table 25.
Reset Value= 0000 0000b
37
7663E–8051–10/08
FSTA Register
Table 24. FSTA Register
FSTA Register (S:D3h)
Flash Status Register
7
6
5
4
3
2
1
0
FMR
-
-
-
-
FSE
FLOAD
FBUSY
Bit Number
Bit
Mnemonic
Description
Flash Movc Redirection
7
FMR
When code is executed from RM0 (and only RM0), this bit allow the MOVC instruction to
be redirected to FM0.
Clear this bit to allow MOVC instruction to read FM0
Set this bit to allow MOVC instruction to read RM0
This bit can be written only from RM0 (on-chip ROM bootloader execution).
6-3
2
-
FSE
unused
Flash sequence error
Set by hardware when the flash activation sequencers FCON 5X and MOV FCON AX) is
not correct (See Error Report Section)
Clear by software or clear by hardware if the last activation sequence was correct
(previous error is canceled)
1
0
FLOAD
FBUSY
Flash Columns latch loaded
Set by hardware when the first data is loaded in the column latches.
Clear by hardware when the activation sequence succeeds (flash write success, or reset
column latch success)
Flash Busy
Set by hardware when programming is in progress.
Clear by hardware when programming is done.
Can not be changed by software.
Reset Value= ‘R’xxx x000b
Where ‘R’ depends on the reset conditions: If RM0 is executed after Reset R=1, if FM0 is executed after reset R=0
38
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Mapping of the
Memory Space
By default, the user space is accessed by MOVC A, @A+DPTR instruction for read only. Setting
FPS bit in FCON register takes precedence on the EXTRAM bit in AUXR register.
The other memory spaces (user, extra row, hardware security) are made accessible in the code
segment by programming bits FMOD2:0 in FCON register in accordance with Table 25. A
MOVC instruction is then used for reading these spaces.
Thanks to the columns latches access, it is possible to write FM0 array, HSB and extra row
blocks. The column latches space is made accessible by setting the FPS bit in FCON register.
Writing is possible from 0000h to FFFFh, address bits 6 to 0 are used to select an address within
a page while bits 14 to 7 are used to select the programming address of the page.
Table 25. .FM0 blocks select bits
FMOD2
FMOD1
FMOD0
Adressable Space
0
0
0
FM0 array(0000h-FFFFh)
0
0
1
Extra Row(00h-80h)
0
1
0
Erase FM0
0
1
1
Column latches reset
1
0
0
HSB
1
0
1
FCB
1
1
0
1
1
1
Reserved
39
7663E–8051–10/08
Launching flash
commands (activation
sequence)
FPL3:0 bits in 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 operation.
This sequence is 5xh followed by Axh. Table 26 summarizes the memory spaces to program
according to FMOD2:0 bits.
Table 26. FM0 Programming Sequences
Write to FCON
FPL3:0
FPS
FMOD2
FMOD1
FMOD0
Operation
5
X
0
0
0
No action
A
X
0
0
0
Write the column latches in FM0
5
X
0
0
1
No action
A
X
0
0
1
Write the column latches in FM0
extra row space
5
X
0
1
0
No action
A
X
0
1
0
Full erase FM0 memory area
Reset
5
X
0
1
1
No action
FM0
Column
Latches
A
X
0
1
1
Reset the FM0 column latches
5
X
1
0
0
No action
A
X
1
0
0
Write the hardware Security byte
(HSB) See (4)
5
X
1
0
1
No action
A
X
1
0
1
Write the Fuse Configuration Byte
(FCB)
5
X
1
1
0
A
X
1
1
0
5
X
1
1
1
A
X
1
1
1
FM0
XAF
FM0
Erase FM0
HSB
FCB
Reserved
No action
Reserved
Note:
1. The sequence 5xh and Axh must be executed without instructions between them otherwise
the programming is not executed (see flash status register).
2. The sequence 5xh and Axh can be executed with the different FMOD0, FMOD1 values, the
last FMOD1:0 value latches the destination target.
3. When the FMOD2 bit is set (corresponding to the serial number field code) no write operation
can be performed.
4. Only the bits corresponding to the previously “full erase” memory space can be written to one.
40
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Loading the Column
Latches
Any number of data from 0 byte to 128 bytes can be loaded in the column latches. The data written in the column latches can be written in a none consecutive order. The DPTR allows to select
the address of the byte to load in the column latches.
The page address to be written (target page in FM0) is given by the last address loaded in the
column latches and when this page belongs to the upper 32K bytes of the logical addressable
MCU space, the target memory bank selection is performed upon the MBO2:0 value during the
last address loaded.
When 0 byte is loaded in the column latches the activation sequence (5xh, Axh in FCON) does
not launch any operations. The FSE bit in FSTA register is set.
When a current flash write operation is on-going (FBUSY is set), it is impossible to load the columns latches before the end of flash programming process (the write operation in the columns
latches is not performed, and the previous columns latches content is not overwritten).
When programming is launched, an automatic erase of the entire memory page is first performed, then programming is effectively done. Thus no page or block erase is needed and only
the loaded data are programmed in the corresponding page. The unloaded data of the target
memory page are programmed at 0xFF value (automatic page erase value).
The following procedure is used to load the column latches and is summarized in Figure 13:
•
Disable interrupt and map the column latch space by setting FPS bit.
•
Select the target memory bank (for page address larger than 32K)
•
Map the column latch
•
Reset the column latch
•
Load the DPTR with the address to write.
•
Load Accumulator register with the data to write.
•
Execute the MOVX @DPTR, A instruction, and only this one (no MOVX @Ri, A).
•
If needed loop the last three instructions until the page is completely loaded.
•
Unmap the column latch if needed (it can be left mapped) and Enable Interrupt
41
7663E–8051–10/08
Figure 13. Column Latches Loading Procedure
Column Latches
Loading
Save & Disable IT
EA= 0
Select target bank
MB2:0=YY
Column Latches Reset
FCON= 53h (FPS=0)
FCON= ABh (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 and default
target memory bank
Note:
The last page address used when loading the column latch is the one used to select the page programming address.
Note:
The value of MB02:0 during the last load gives the upper 32K bytes bank target selection.
Note:
The execution of this sequence when BUSY flag is set leads to the no-execution of the write in the
column latches (the previous loaded data remains unchanged).
Writing the Flash
Spaces
User
42
The following procedure is used to program the User space and is summarized in Figure 14:
•
Load up to one page of data in the column latches from address 0000h to FFFFh (see
Figure 13.).
•
Disable the interrupts.
•
Launch the programming by writing the data sequence 50h followed by A0h in FCON
register.
The end of the programming indicated by the FBUSY flag cleared.
•
Enable the interrupts.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Extra Row
The following procedure is used to program the Extra Row space and is summarized in
Figure 14:
•
Load data in the column latches from address FF80h to FFFFh.
•
Disable the interrupts.
•
Launch the programming by writing the data sequence 51h followed by A1h in FCON
register.
The end of the programming indicated by the FBUSY flag cleared.
•
Enable the interrupts.
Figure 14. Flash and Extra row Programming Procedure
Hardware Security Byte
(HSB)
Flash
Programming
XROW
Programming
Column Latches Loading
see Figure 13
Column Latches Loading
see Figure 13
Save & Disable IT
EA= 0
Save & Disable IT
EA= 0
Launch Programming
FCON= 50h
FCON= A0h
Launch Programming
FCON= 51h
FCON= A1h
FBusy
Cleared?
FBusy
Cleared?
Clear Mode
FCON = 00h
Clear Mode
FCON = 00h
End Programming
Restore IT
End Programming
Restore IT
The following procedure is used to program the Hardware Security Byte space and is
summarized in Figure 15:
•
Set FPS and map Hardware byte (FCON = 0x0C)
•
Save and disable the interrupts.
•
Load DPTR at address 0000h
•
Load Accumulator register with the data to load.
•
Execute the MOVX @DPTR, A instruction.
43
7663E–8051–10/08
•
Launch the programming by writing the data sequence 54h followed by A4h in FCON
register.
The end of the programming indicated by the FBusy flag cleared.
•
Restore the interrupts
.
Figure 15. Hardware Security Byte Programming Procedure
HSB
Programming
Save & Disable IT
EA= 0
FCON = 0Ch
Data Load
DPTR= 00h
ACC= Data
Exec: MOVX @DPTR, A
Launch Programming
FCON= 54h
FCON= A4h
FBusy
Cleared?
Clear Mode
FCON = 00h
End Programming
RestoreIT
Fuse Configuration Byte
(FCB)
44
The following procedure is used to program the Fuse Configuration Byte space and is
summarized in Figure 16:
•
Set FPS and map FCB (FCON = 0x0D)
•
Save and disable the interrupts.
•
Load DPTR at address 0000h
•
Load Accumulator register with the data to load.
•
Execute the MOVX @DPTR, A instruction.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
•
Launch the programming by writing the data sequence 55h followed by A5h in FCON
register.
The end of the programming indicated by the FBusy flag cleared.
•
Restore the interrupts
.
Figure 16. Fuse Configuration Byte Programming Procedure
FCB
Programming
Save & Disable IT
EA= 0
FCON = 0Dh
Data Load
DPTR= 00h
ACC= Data
Exec: MOVX @DPTR, A
Launch Programming
FCON= 55h
FCON= A5h
FBusy
Cleared?
Clear Mode
FCON = 00h
End Programming
RestoreIT
Reset of columns
latches space
No automatic reset of the columns latches is performed after a successful flash write
process. Resetting the columns latches during a flash write process is mandatory. User
shall implement a reset of the column latch before each column latch load sequence.
45
7663E–8051–10/08
In addition, the user application can reset the columns latches space manually. The following procedure is used to reset the columns latches space
Launch the programming by writing the data sequence 53h followed by A3h in FCON
register (from FM0 and RM0).
46
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Errors Report /
Miscellaneous states
Flash Busy flag
The FBUSY flag indicates on-going flash write operation.
The busy flag is set by hardware, the hardware clears this flag after the end of the programming
operation.
Flash Programming
Sequence Error
When a wrong sequence is detected the FSE in FSTA is set.
The following events are considered as not correct activation sequence:
- The two “MOV FCON,5x and MOV FCON, Ax” were not consecutive, or the second instruction
differs from “MOV FCON Ax” (for example, an interrupt occurs during the sequence).
- The sequence (write flash or reset column latches) occurred with no data loaded in the column
latches
The FSE bit can be cleared:
- By software
- By hardware when a correct programming sequence occurs.
Note: When a good sequence occurs just after an incorrect sequence, the previous error is lost.
The user software application should take care to check the FSE bit before initiating a new
sequence.
Power Down Mode
Request
In Power Down mode, the on-chip flash memory is deselected (to reduce power consumption),
this leads to the lost of the columns latches content.
In this case, if columns latches were previously loaded they are reset: FLOAD bit in FSTA register should be reset after power down mode.
If a power down mode is requested during flash programming (FBUSY=1), all power down
sequence instructions should be ignored until the end of flash process.
47
7663E–8051–10/08
Reading the Flash
Spaces
User
The following procedure is used to read the User space:
•
Read one byte in Accumulator by executing MOVC A,@A+DPTR
Note:
FCON is supposed to be reset when not needed.
Depending of the MBO2:0 bits, the MOVC A,@A+DPTR can address a specific upper 32K bytes
bank. It allows to read the 32K bytes upper On-chip flash memory from one bank to another one.
When read from the bootloader area, the user memory shall be mapped before any read access
by setting the FMR bit of the FSTA register.
By default, when the bootloader is entered by hardware conditions, the ROM area is mapped for
MOVC A,@A+DPTR operations. It is necessary to remap the user memory before each read
access.
Extra Row (XAF)
The following procedure is used to read the Extra Row space and is summarized in Figure 17:
•
Map the Extra Row space by writing 01h in FCON register.
•
Read one byte in Accumulator by executing MOVC A,@A+DPTR with A= 0 & DPTR= 0000h
to 007Fh.
•
Clear FCON to unmap the Extra Row.
Figure 17. XAF Reading Procedure
XRAW Reading
XRAW Mapping
FCON = 01h
Data Read
DPTR= @ (00h up to 7Fh
ACC= 0
Exec: MOVC A, @A+DPTR
XRAW Unmapping
FCON = 00h (FPS = 0)
Hardware Security Byte
48
The following procedure is used to read the Hardware Security space and is summarized in Figure 18:
•
Map the Hardware Security space by writing 04h in FCON register.
•
Read the byte in Accumulator by executing MOVC A,@A+DPTR with A= 0 & DPTR= 0000h.
•
Clear FCON to unmap the Hardware Security Byte.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Figure 18. HSB Reading Procedure
HSB Reading
HSB Mapping
FCON = 04h
Data Read
DPTR= 0000h
ACC= 00h
Exec: MOVC A, @A+DPTR
HSB Unmapping
FCON = 00h (FPS = 0)
Fuse ConfigurationByte
The following procedure is used to read the Fuse Configuration byte and is summarized
in Figure 18:
•
Map the FCB by writing 05h in FCON register.
•
Read the byte in Accumulator by executing MOVC A,@A+DPTR with A= 0 & DPTR= 0000h.
•
Clear FCON to unmap the Hardware Security Byte.
HSB Reading Procedure
FCB Reading
FCB Mapping
FCON = 05h
Data Read
DPTR= 0000h
ACC= 00h
Exec: MOVC A, @A+DPTR
HSB Unmapping
FCON = 00h (FPS = 0)
49
7663E–8051–10/08
Operation Cross Memory Access
Space addressable in read and write are:
•
RAM
•
ERAM (Expanded RAM access by movx)
•
XRAM (eXternal RAM)
•
FM0 (user flash)
•
Hardware byte
•
XROW FM0
•
Boot RM0
•
Flash Column latch
The table below provide the different kind of memory which can be accessed from different code
location.
Table 27. Cross Memory Access
XRAM
Action
RAM
ERAM
boot RM0
FM0
HSB
FCB
XAF FM0
Read
ok
ok
ok
ok
ok
ok
ok
Write
ok
ok
-
ok (RWW)
ok (RWW)
ok (RWW)
ok (RWW)
Read
ok
ok
-
ok
ok
ok
ok
Write
ok
ok
-
ok (idle)
ok
ok
ok
Read
ok
ok
-
-
-
-
-
Write
ok
ok
-
-
-
-
-
boot RM0
FM0
External
memory
EA = 0
or BANK3
Sharing Instructions
Table 28. Instructions shared
Action
RAM
XRAM
RM0
CL FM0
FM0
HSB
XAF FM0
Read
MOV
MOVX
A,@DPTR
MOVC A,
@A+DPTR
-
MOVC A,
@A+DPTR
MOVC A,
@A+DPTR
MOVC A,
@A+DPTR
Write
MOV
MOVX
@DPTR,A
-
MOVX
@DPTR,A
by CL
by CL
by CL
FM0
FM0
FM0
Note:
50
by cl: using Column Latch
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 29. Write MOVX @DPTR,A
FPS of
FCCON
EA
XRAM
ERAM
0
X
winner
CL FM0
1
winner
1
0
winner
Table 30. MOVC A, @A+DPTR executed from External code EA=0
FMOD2:0
FBS
(Fetch)
MBO
(Target)
MOVC A,@A+DPTR
X
X
X
Read External Code
Table 31. MOVC A, @A+DPTR executed from External code EA=1, PC>=0x8000, FBS=Bank3
FMOD2:0
MBO
(Target)
DPTR
MOVC A,@A+DPTR
X
X
< 0x8000
Depends on FLB2:0
Can Returns Random value, for secured part.
X
>= 0x8000
External code read
51
7663E–8051–10/08
Flash Protection from Parallel Programming
The three lock bits in Hardware Security Byte (see "In-System Programming" section) are programmed according to Table 32 provide different level of protection for the on-chip flash memory
FM0.
They are set by default to level 4
Table 32. Program Lock Bit FLB2-0
Program Lock Bits
Security
level
FLB0
FLB1
FLB2
1
U
U
U
No program lock features enabled.
U
MOVC instruction executed from external program memory are disabled from
fetching code bytes from internal memory, EA is sampled and latched on reset,
and further parallel programming of the Flash is disabled.
2
P
U
Protection Description
ISP allows only flash verification (no write operations are allowed) but IAP from
internal code still allowed.
3
U
P
U
Same as 2, also verify through parallel programming interface is disabled and
ISP read operation not allowed.
4
U
U
P
Same as 3, also external execution is disabled (external bank not accessible)
Program Lock bits
U: unprogrammed
P: programmed
WARNING: Security level 2 and 3 should only be programmed after verification.
52
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Bootloader Architecture
Introduction
The bootloader manages a communication between a host platform running an ISP tool and a
AT89C51RE2 target.
The bootloader implemented in AT89C51RE2 is designed to reside in the dedicated ROM bank.
This memory area can only be executed (fetched) when the processor enters the boot process.
The implementation of the bootloader is based on standard set of libraries including INTEL hex
based protocol, standard communication links and ATMEL ISP command set.
Figure 19. Bootloader Functional Description
External Host with
Specific Protocol
Communication
ISP Communication
Management
Bootloader
Memory
Management
Memory
On the above diagram, the on-chip bootloader processes are:
•
ISP Communication Management
The purpose of this process is to manage the communication and its protocol between the onchip bootloader and a external device. The on-chip ROM implement a serial protocol (see section Bootloader Protocol). This process translate serial communication frame (UART) into Flash
memory access (read, write, erase...).
•
Memory Management
This process manages low level access to Flash memory (performs read and write access).
53
7663E–8051–10/08
Bootloader
Description
Entry points
After reset only one bootloader entry point is possible. This entry point stands at address 0x0000
of the boot ROM memory. This entry point executes the boot process of the bootloader.
The bootloader entry point can be selected through two processes:
At reset, if the hardware conditions are applied, the bootloader entry point is accessed and
executed.
At reset, if the hardware conditions are not set and the BRV2-0 is programmed ‘011’, the bootloader entry point is accessed and the bootprocess is started.
Boot Process
Description
The boot process consists in three main operations:
•
The hardware boot process request detection
•
The communication link detection (Uart or OCD)
•
The start-up of the bootloader
No
No
Yes
PC = RM0 @0x0000h
No
BRV=’101’
BRV=’110’
Yes
Yes
Yes
PC = FM0 Bank0
@0xFFFCh
Yes
No
BRV=’100’
PC = FM0 Bank0
@0xFFFCh
BRV=’011’
PC = FM0 Bank1
@0xFFFCh
No
EA=1
PSEN=0
PC = FM0 Bank2
@0xFFFCh
Hardware
Boot Process
RESET
Communication link
detector / initialiser
Start Bootloader
Start Application
Hardware boot process
request detection
The hardware boot process request is detected when the hardware conditions (under reset,
EA=1 and PSEN=0) are received by the processor or when no hardware condition is applied
and the BRV2:0 is configured ‘011’.
Communication link
detection
Two interfaces are available for ISP:
54
•
UART0
•
OCD UART
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
The communication link detection is done by a circular polling on all the interfaces. On
AT89C51RE2, the ISP interfaces are all based on simple UART mechanisms (Rx, Tx).
The Rx line default state is ‘1’ when no communication is in progress. A transition from ‘1’ to ‘0’
on the Rx line indicates a start of frame.
Once one of the interface detects a starts of frame (‘0’) on its Rx line, the interface is selected
and configuration of the communication link starts.
Figure 20. Communication link Detection
Detection
Start
Interface 1
SF = 0
Yes
No
Interface 2
SF = 0
No
Yes
Interface 2
Initialisation
Interface 1
Initialisation
Start Bootloader
Notes:
1. SF: Start of Frame (‘0’ = detected; ‘1’ = not detected)
2. In AT89C51RE2 implementation, Interface 1 refers to UART0 and Interface 2 refers to the
OCD UART interface.
55
7663E–8051–10/08
ISP Protocol
Description
Physical Layer
The UART used to transmit information has the following configuration:
•
Frame Description
Character: 8-bit data
•
Parity: none
•
Stop: 1 bit
•
Flow control: none
•
Baud rate: autobaud is performed by the bootloader to compute the baud rate chosen by the
host.
The Serial Protocol is based on the Intel Extended Hex-type records.
Intel Hex records consist of ASCII characters used to represent hexadecimal values and are
summarized below.
Table 33. Intel Hex Type Frame
•
Record Mark ‘:’
Record length
Load Offset
Record Type
Data or Info
Checksum
1 byte
1 byte
2 bytes
1 bytes
n byte
1 byte
Record Mark:
–
•
Record length:
–
•
•
–
Load Offset specifies the 16-bit starting load offset of the data Bytes, therefore this
field is used only for
–
Data Program Record.
Record Type:
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:
–
56
Record Type specifies the command type. This field is used to interpret the
remaining information within the frame.
Data/Info:
–
•
Record length specifies the number of Bytes of information or data which follows the
Record Type field of the record.
Load Offset:
–
•
Record Mark is the start of frame. This field must contain’:’.
Checksum is the two’s complement of the 8-bit Bytes that result from converting
each pair of ASCII hexadecimal digits to one Byte of binary, thus including all field
from the Record Length field to the last Byte of the Data/Info field. Therefore, the
sum of all the ASCII pairs in a record after converting to binary, including all field from
the Record Length field to the Checksum field, is zero.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Protocol
Overview
An initialization step must be performed after each Reset. After microcontroller reset, the bootloader waits for an autobaud sequence (see Section “Autobaud Performances”).
When the communication is initialized the protocol depends on the record type issued by the
host.
Communication
Initialization
The host initiates the communication by sending a ’U’ character to help the bootloader to compute the baudrate (autobaud).
Figure 21. Initialization
Bootloader
Host
Autobaud
Performances
Init Communication
“U”
If (not received “U”)
Else
Communication Opened
“U”
Performs Autobaud
Sends Back ‘U’ Character
The bootloader supports a wide range of baud rates. 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.
Command Data Stream Protocol
All commands are sent using the same flow. To increase performance, the echo has been
removed from the bootloader response.
Figure 22. 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
Gets frame, and sends back echo
for each received Byte
Each command flow may end with:
57
7663E–8051–10/08
58
•
“X”: If checksum error
•
“L”: If read security is set
•
“P”: If program security is set
•
“.”: If command ok
•
byte + “.”: read byte ok
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Reading/Blank
checking memory
To start the reading or blank checking operation,
Requests from Host
Command
Record
Type
Record
Length
Offset
04h
05h
0000h
Data[0]
Data[1]
Data[2]
Data[3]
Data[4]
Read selected memory
00h
Start Address
End Address
Blank Check selected memory
Answers from
Bootloader
01h
The boot loader can answer to a read command with:
•
‘Address = data ‘& ‘CR’ &’LF’ the number of data by line depends of the bootloader.
•
‘X’ & ‘CR’ & ‘LF’ if the checksum is wrong
•
‘L’ & ‘CR’ & ‘LF’ if the Security is set
The bootloader answers to blank check command:
Changing
memory/page
•
‘.’ & ‘CR’ &’LF’ when the blank check is ok
•
‘First Address wrong’ ‘CR’ & ‘LF’ when the blank check is fail
•
‘X’ & ‘CR’ & ‘LF’ if the checksum is wrong
•
‘L’ & ‘CR’ & ‘LF’ if the Security is set
To change the memory selected and/or the page, the Host can send two commands.
•
Select New Page to keep the same memory.
•
Select Memory to change the Memory and page
Requests from Host
Record
Type
Record
Length
Offset
Data[0]
Data[1]
Select New Page
02h
02h
start
address
Page (4
bits) + 0h
00h
Select Memory
04h
02h
0000h
Command
Answers from
Bootloader
Memory
space
Page
The boot loader can answer to a read command with:
•
‘. ‘& ‘CR’ &’LF’ if the command is done
•
‘X’ & ‘CR’ & ‘LF’ if the checksum is wrong
59
7663E–8051–10/08
Programming/Erasing
memory
Requests from Host
Command
Answers from
Bootloader
Starting application
Record
Type
Record
Length
Offset
Data[0]
Data[1]
Data[2]
Data[3]
Data[4]
Program selected memory
00h
nb of
data
start
address
x
x
x
x
x
Erase selected memory
04h
05h
0000h
00h
FFh
00h
00h
02h
The boot loader answers with:
•
‘.’ & ‘CR’ &’LF’ when the data are programmed
•
‘X’ & ‘CR’ & ‘LF’ if the checksum is wrong
•
‘P’ & ‘CR’ & ‘LF’ if the Security is set
The application can only be started by a Watchdog reset.
No answer is returned by the bootloader.
Requests from Host
Record
Command
Start application with watchdog
60
Record Type
Length
Offset
01h
00h
0000h
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
ISP Commands description
Select Memory Space
The ‘Select Memory Space’ command allows to route all read, write commands to a selected
area. For each area (Family) a code is defined. This code corresponds to the memory area
encoded value in the INTEL HEX frame.
The area supported and there coding are listed in the table below.
Table 34. Memory Families & coding
Memory/Information Family
coding*
name
FLASH
0
MEM_FLASH
SECURITY
7
MEM_PROTECT
CONFIGURATION
8
MEM_CONF
BOOTLOADER
3
MEM_BOOT
SIGNATURE
6
MEM_SIGNATURE
The Bootloader information and the signature areas are read only. The value in the coding column is the value to report in the corresponding protocol field.
Note:
* the coding number doesn’t include any information on the authorized address range of the family. A summary of these addresses is available in appendix (See “Address Mapping” on page 67.)
61
7663E–8051–10/08
Select Page
The ‘ Select Page’ command allows to define a page number in the selected area. A page is
defined as a 64K linear memory space (According to the INTEL HEX format). It doesn’t corresponds to a physical bank from the processor.
The following table summarizes the memory spaces for which the select page command can be
applied.
Table 35. Memory space & Select page
Memory/Information Family
FLASH
62
Comments/Restriction
page 0 (0->64K) and 1(64k->128k) available
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Write commands
The following table summarizes the memory spaces for which the write command can be
applied.
Table 36. Memory space & Select page
Memory/Information Family
Comments/Restriction
FLASH
need security level check
SECURITY
only a higher level can be write
CONFIGURATION
In case of write command to other area, nothing is done.
The bootloader returns a Write protection (‘P’) if the SECURITY do not allow any write operation
from the bootloader.
FLASH
The program/data Flash memory area can be programmed by the bootloader by data pages of
up to 128bytes.
If the Flash memory security level is at least ‘2’ (FLB2:0 = ‘110’), no write operation can be performed through the bootloader.
Table 37. Flash Write Authorization Summary
Security level (HSB)
FLB2:0
Command
Write
111
Allowed
110
101
011
Forbidden
Forbidden
Forbidden
CONFIGURATION
The FCB configuration byte can always be written, whatever are the security levels.
SECURITY
The Security byte can always be written with a value that enables a protection higher than the
previous one.
If attempting to write a lower security, no action is performed and the bootloader returns a protection error code (‘P’)
Table 38. Security Write Authorization Summary
Security level (HSB)
to FLB2:0
write from
FLB2:0
111
110
101
011
111
Allowed
Allowed
Allowed
Allowed
110
Forbidden
Allowed
Allowed
Allowed
101
Forbidden
Forbidden
Allowed
Allowed
011
Forbidden
Forbidden
Forbidden
Allowed
63
7663E–8051–10/08
Erasing commands
The erasing command is supported by the following areas:
Table 39. Memory space & Erase
Memory/Information Family
FLASH
Comments/Restriction
need security level check
Nothing is done on the other areas.
FLASH
The erasing command on the Flash memory:
•
erases the four physical flash memory banks (from address 0000h to 1FFFFh).
•
the HSB (Hardware Security Byte) is set at NO_PROTECTION:
–
64
FLB2.0 = ‘111’
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Blank Checking
commands
The blank checking command is supported by the following areas
Table 40. Memory space & Erase
Memory/Information Family
Comments/Restriction
FLASH
need security level check
Nothing is done on the other areas.
The first not erased address is returned if the blank check is failed.
FLASH
The blank checking command on the Flash memory can be done from address 0000h to
1FFFFh.
The blank check operation is only possible if the HSB (Hardware Security Byte) has a security
level lower than or equal to ‘2’ (FLB2.0 = ‘110’)
Table 41. Flash Blank check Authorization Summary
Security level (HSB)
FLB2:0
Command
Blank Check
111
Allowed
110
Allowed
101
011
Forbidden
Forbidden
65
7663E–8051–10/08
Reading commands
The reading command is supported by the following areas:
Table 42. Memory space & Select page
Memory/Information Family
Comments/Restriction
FLASH
need security level check
SECURITY
CONFIGURATION
BOOTLOADER
SIGNATURE
FLASH
The reading command on the Flash memory can be done from address 000h to 1FFFFh. The
read operation is only possible if the HSB (Hardware Security Byte) has a security level lower
than or equal to ‘2’ (FLB2.0 = ‘110’)
Table 43. Flash Read Authorization Summary
Security level (HSB)
FLB2:0
Command
Read
111
Allowed
110
Allowed
101
011
Forbidden
Forbidden
CONFIGURATION
The CONFIGURATION family can always be read.
SECURITY
The SECURITY family can always be read.
BOOTLOADER
All the field from the BOOTLOARED family can be read from the bootloader. Each bootloader
information shall be read unitary. Accesses must be done byte per byte according to the address
definition
SIGNATURE
All the field from the SIGNATURE family can be read from the bootloader. Each signature information shall be read unitary. Accesses must be done byte per byte according to the address
definition
66
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Start Application
The start application command is used to quit the bootloader and start the application loaded.
The start application is performed by a watchdog reset.
The best way to start the application from a user defined entry point is to configure the FCB
(Fuse Configuration Byte) before launching the watchdog. Then, depending on the configuration
of the BRV2:0 field, the hardware boots from the selected memory area.
ISP Command
summary
UART Protocol frames
Table 44. Summary of frames from Host
Record
Type
Record
Length
Offset
Data[0]
Data[1]
Data[2]
Data[3]
Data[4]
Program selected memory
00h
nb of data
start
address
x
x
x
x
x
Start application with watchdog
01h
00h
0000h
x
x
x
x
x
Select New Page
02h
02h
start
address
Page (4
bits) + 0h
00h
x
x
x
02h
0000h
Page
x
x
x
Command
Select Memory
Read selected memory
Memory
space
00h
04h
Start Address
Blank Check selected memory
05h
End Address
01h
0000h
Erase Selected memory
00h
FFh
00h
00h
02h
Address Mapping
Table 45. Memory Families, Addresses & Coding
Memory/Information
Family
Memory/Parameter
coding
Address
Page number
FLASH
0
0 up to 0x1FFFF
0 up to 1
HSB
7
0
0
SECURITY
FCB
8
0
0
CONFIGURATION
0
BOOTLOADER
0
SIGNATURE
Bootloader revision
Boot id1
FLASH
00h
3
01h
Boot id2
02h
Manuf. code
30h
Family code
31h
6
Product name
60h
Product rev
61h
Attempting an access with any other ‘coding’, ‘page number’ or ‘Address’ results in no action
and no answer from the bootloader.
67
7663E–8051–10/08
Timers/Counters
The AT89C51RE2 implements two general-purpose, 16-bit Timers/Counters. Such are identified
as Timer 0 and Timer 1, and can be independently configured to operate in a variety of modes
as a Timer or an event Counter. When operating as a Timer, the Timer/Counter runs for a programmed length of time, then issues an interrupt request. When operating as a Counter, the
Timer/Counter counts negative transitions on an external pin. After a preset number of counts,
the Counter issues an interrupt request.
The various operating modes of each Timer/Counter are described in the following sections.
Timer/Counter
Operations
A basic operation is Timer registers THx and TLx (x = 0, 1) connected in cascade to form a 16bit Timer. Setting the run control bit (TRx) in TCON register (see Figure 46) turns the Timer on
by allowing the selected input to increment TLx. When TLx overflows it increments THx; when
THx overflows it sets the Timer overflow flag (TFx) in TCON register. Setting the TRx does not
clear the THx and TLx Timer registers. Timer registers can be accessed to obtain the current
count or to enter preset values. They can be read at any time but TRx bit must be cleared to preset their values, otherwise the behavior of the Timer/Counter is unpredictable.
The C/Tx# control bit selects Timer operation or Counter operation by selecting the divideddown peripheral clock or external pin Tx as the source for the counted signal. TRx bit must be
cleared when changing the mode of operation, otherwise the behavior of the Timer/Counter is
unpredictable.
For Timer operation (C/Tx# = 0), the Timer register counts the divided-down peripheral clock.
The Timer register is incremented once every peripheral cycle (6 peripheral clock periods). The
Timer clock rate is FPER/6, i.e. FOSC/12 in standard mode or FOSC/6 in X2 mode.
For Counter operation (C/Tx# = 1), the Timer register counts the negative transitions on the Tx
external input pin. The external input is sampled every peripheral cycles. When the sample is
high in one cycle and low in the next one, the Counter is incremented. Since it takes 2 cycles (12
peripheral clock periods) to recognize a negative transition, the maximum count rate is FPER/12,
i.e. FOSC/24 in standard mode or FOSC/12 in X2 mode. There are no restrictions on the duty cycle
of the external input signal, but to ensure that a given level is sampled at least once before it
changes, it should be held for at least one full peripheral cycle.
Timer 0
Timer 0 functions as either a Timer or event Counter in four modes of operation. Figure 23 to
Figure 26 show the logical configuration of each mode.
Timer 0 is controlled by the four lower bits of TMOD register (see Figure 47) and bits 0, 1, 4 and
5 of TCON register (see Figure 46). TMOD register selects the method of Timer gating (GATE0),
Timer or Counter operation (T/C0#) and mode of operation (M10 and M00). TCON register provides Timer 0 control functions: overflow flag (TF0), run control bit (TR0), interrupt flag (IE0) and
interrupt type control bit (IT0).
For normal Timer operation (GATE0 = 0), setting TR0 allows TL0 to be incremented by the
selected input. Setting GATE0 and TR0 allows external pin INT0# to control Timer operation.
Timer 0 overflow (count rolls over from all 1s to all 0s) sets TF0 flag generating an interrupt
request.
It is important to stop Timer/Counter before changing mode.
68
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Mode 0 (13-bit Timer)
Mode 0 configures Timer 0 as an 13-bit Timer which is set up as an 8-bit Timer (TH0 register)
with a modulo 32 prescaler implemented with the lower five bits of TL0 register (see Figure 23).
The upper three bits of TL0 register are indeterminate and should be ignored. Prescaler overflow
increments TH0 register.
Figure 23. Timer/Counter x (x = 0 or 1) in Mode 0
See the “Clock” section
FTx
CLOCK
÷6
0
THx
(8 bits)
1
TLx
(5 bits)
Overflow
TFx
TCON reg
Tx
Timer x
Interrupt
Request
C/Tx#
TMOD reg
INTx#
GATEx
TRx
TMOD reg
Mode 1 (16-bit Timer)
TCON reg
Mode 1 configures Timer 0 as a 16-bit Timer with TH0 and TL0 registers connected in cascade
(see Figure 24). The selected input increments TL0 register.
Figure 24. Timer/Counter x (x = 0 or 1) in Mode 1
See the “Clock” section
FTx
CLOCK
÷6
0
THx
(8 bits)
1
Tx
TLx
(8 bits)
Overflow
TFx
TCON reg
Timer x
Interrupt
Request
C/Tx#
TMOD reg
INTx#
GATEx
TMOD reg
TRx
TCON reg
69
7663E–8051–10/08
Mode 2 (8-bit Timer
with Auto-Reload)
Mode 2 configures Timer 0 as an 8-bit Timer (TL0 register) that automatically reloads from TH0
register (see Figure 25). TL0 overflow sets TF0 flag in TCON register and reloads TL0 with the
contents of TH0, which is preset by software. When the interrupt request is serviced, hardware
clears TF0. The reload leaves TH0 unchanged. The next reload value may be changed at any
time by writing it to TH0 register.
Figure 25. Timer/Counter x (x = 0 or 1) in Mode 2
See the “Clock” section
FTx
CLOCK
÷6
0
TLx
(8 bits)
1
Overflow
TFx
TCON reg
Tx
Timer x
Interrupt
Request
C/Tx#
TMOD reg
INTx#
GATEx
THx
(8 bits)
TRx
TMOD reg
TCON reg
Mode 3 (Two 8-bit
Timers)
Mode 3 configures Timer 0 such that registers TL0 and TH0 operate as separate 8-bit Timers
(see Figure 26). This mode is provided for applications requiring an additional 8-bit Timer or
Counter. TL0 uses the Timer 0 control bits C/T0# and GATE0 in TMOD register, and TR0 and
TF0 in TCON register in the normal manner. TH0 is locked into a Timer function (counting FPER
/6) and takes over use of the Timer 1 interrupt (TF1) and run control (TR1) bits. Thus, operation
of Timer 1 is restricted when Timer 0 is in mode 3.
Figure 26. Timer/Counter 0 in Mode 3: Two 8-bit Counters
FTx
CLOCK
÷6
0
1
TL0
(8 bits)
Overflow
TH0
(8 bits)
Overflow
TF0
TCON.5
T0
Timer 0
Interrupt
Request
C/T0#
TMOD.2
INT0#
GATE0
TMOD.3
FTx
CLOCK
÷6
See the “Clock” section
70
TR0
TCON.4
TF1
TCON.7
Timer 1
Interrupt
Request
TR1
TCON.6
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Timer 1
Timer 1 is identical to Timer 0 excepted for Mode 3 which is a hold-count mode. The following
comments help to understand the differences:
•
Timer 1 functions as either a Timer or event Counter in three modes of operation. Figure 23
to Figure 25 show the logical configuration for modes 0, 1, and 2. Timer 1’s mode 3 is a
hold-count mode.
•
Timer 1 is controlled by the four high-order bits of TMOD register (see Figure 47) and bits 2,
3, 6 and 7 of TCON register (see Figure 46). TMOD register selects the method of Timer
gating (GATE1), Timer or Counter operation (C/T1#) and mode of operation (M11 and M01).
TCON register provides Timer 1 control functions: overflow flag (TF1), run control bit (TR1),
interrupt flag (IE1) and interrupt type control bit (IT1).
•
Timer 1 can serve as the Baud Rate Generator for the Serial Port. Mode 2 is best suited for
this purpose.
•
For normal Timer operation (GATE1 = 0), setting TR1 allows TL1 to be incremented by the
selected input. Setting GATE1 and TR1 allows external pin INT1# to control Timer operation.
•
Timer 1 overflow (count rolls over from all 1s to all 0s) sets the TF1 flag generating an
interrupt request.
•
When Timer 0 is in mode 3, it uses Timer 1’s overflow flag (TF1) and run control bit (TR1).
For this situation, use Timer 1 only for applications that do not require an interrupt (such as a
Baud Rate Generator for the Serial Port) and switch Timer 1 in and out of mode 3 to turn it
off and on.
•
It is important to stop Timer/Counter before changing mode.
Mode 0 (13-bit Timer)
Mode 0 configures Timer 1 as a 13-bit Timer, which is set up as an 8-bit Timer (TH1 register)
with a modulo-32 prescaler implemented with the lower 5 bits of the TL1 register (see
Figure 23). The upper 3 bits of TL1 register are ignored. Prescaler overflow increments TH1
register.
Mode 1 (16-bit Timer)
Mode 1 configures Timer 1 as a 16-bit Timer with TH1 and TL1 registers connected in cascade
(see Figure 24). The selected input increments TL1 register.
Mode 2 (8-bit Timer
with Auto-Reload)
Mode 2 configures Timer 1 as an 8-bit Timer (TL1 register) with automatic reload from TH1 register on overflow (see Figure 25). TL1 overflow sets TF1 flag in TCON register and reloads TL1
with the contents of TH1, which is preset by software. The reload leaves TH1 unchanged.
Mode 3 (Halt)
Placing Timer 1 in mode 3 causes it to halt and hold its count. This can be used to halt Timer 1
when TR1 run control bit is not available i.e. when Timer 0 is in mode 3.
Interrupt
Each Timer handles one interrupt source that is the timer overflow flag TF0 or TF1. This flag is
set every time an overflow occurs. Flags are cleared when vectoring to the Timer interrupt routine. Interrupts are enabled by setting ETx bit in IEN0 register. This assumes interrupts are
globally enabled by setting EA bit in IEN0 register.
71
7663E–8051–10/08
Figure 27. Timer Interrupt System
Timer 0
Interrupt Request
TF0
TCON.5
ET0
IEN0.1
Timer 1
Interrupt Request
TF1
TCON.7
ET1
IEN0.3
72
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Registers
Table 46. TCON Register
TCON (S:88h)
Timer/Counter Control Register
7
6
5
4
3
2
1
0
TF1
TR1
TF0
TR0
IE1
IT1
IE0
IT0
Bit Number
Bit
Mnemonic
Description
7
TF1
Timer 1 Overflow Flag
Cleared by hardware when processor vectors to interrupt routine.
Set by hardware on Timer/Counter overflow, when Timer 1 register overflows.
6
TR1
Timer 1 Run Control Bit
Clear to turn off Timer/Counter 1.
Set to turn on Timer/Counter 1.
5
TF0
Timer 0 Overflow Flag
Cleared by hardware when processor vectors to interrupt routine.
Set by hardware on Timer/Counter overflow, when Timer 0 register overflows.
4
TR0
Timer 0 Run Control Bit
Clear to turn off Timer/Counter 0.
Set to turn on Timer/Counter 0.
3
IE1
Interrupt 1 Edge Flag
Cleared by hardware when interrupt is processed if edge-triggered (see IT1).
Set by hardware when external interrupt is detected on INT1# pin.
2
IT1
Interrupt 1 Type Control Bit
Clear to select low level active (level triggered) for external interrupt 1 (INT1#).
Set to select falling edge active (edge triggered) for external interrupt 1.
1
IE0
Interrupt 0 Edge Flag
Cleared by hardware when interrupt is processed if edge-triggered (see IT0).
Set by hardware when external interrupt is detected on INT0# pin.
0
IT0
Interrupt 0 Type Control Bit
Clear to select low level active (level triggered) for external interrupt 0 (INT0#).
Set to select falling edge active (edge triggered) for external interrupt 0.
Reset Value = 0000 0000b
73
7663E–8051–10/08
Table 47. TMOD Register
TMOD (S:89h)
Timer/Counter Mode Control Register
7
6
5
4
3
2
1
0
GATE1
C/T1#
M11
M01
GATE0
C/T0#
M10
M00
Bit Number
Bit
Mnemonic
Description
7
GATE1
Timer 1 Gating Control Bit
Clear to enable Timer 1 whenever TR1 bit is set.
Set to enable Timer 1 only while INT1# pin is high and TR1 bit is set.
6
C/T1#
Timer 1 Counter/Timer Select Bit
Clear for Timer operation: Timer 1 counts the divided-down system clock.
Set for Counter operation: Timer 1 counts negative transitions on external pin T1.
5
M11
Timer 1 Mode Select Bits
M01
M11
0
0
0
1
1
0
1
1
Operating mode
Mode 0: 8-bit Timer/Counter (TH1) with 5-bit prescaler (TL1).
Mode 1: 16-bit Timer/Counter.
Mode 2: 8-bit auto-reload Timer/Counter (TL1)(1)
Mode 3: Timer 1 halted. Retains count
4
M01
3
GATE0
Timer 0 Gating Control Bit
Clear to enable Timer 0 whenever TR0 bit is set.
Set to enable Timer/Counter 0 only while INT0# pin is high and TR0 bit is set.
2
C/T0#
Timer 0 Counter/Timer Select Bit
Clear for Timer operation: Timer 0 counts the divided-down system clock.
Set for Counter operation: Timer 0 counts negative transitions on external pin T0.
1
M10
0
M00
Timer 0 Mode Select Bit
M00
Operating mode
M10
0
0
Mode 0: 8-bit Timer/Counter (TH0) with 5-bit prescaler (TL0).
0
1
Mode 1: 16-bit Timer/Counter.
1
0
Mode 2: 8-bit auto-reload Timer/Counter (TL0)(2)
1
1
Mode 3: TL0 is an 8-bit Timer/Counter
TH0 is an 8-bit Timer using Timer 1’s TR0 and TF0 bits.
Notes: 1. Reloaded from TH1 at overflow.
2. Reloaded from TH0 at overflow.
Reset Value = 0000 0000b
74
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 48. TH0 Register
TH0 (S:8Ch)
Timer 0 High Byte Register
7
6
5
4
3
2
1
0
–
–
–
–
–
–
–
–
Bit Number
Bit
Mnemonic
Description
7:0
High Byte of Timer 0.
Reset Value = 0000 0000b
Table 49. TL0 Register
TL0 (S:8Ah)
Timer 0 Low Byte Register
7
6
5
4
3
2
1
0
–
–
–
–
–
–
–
–
Bit Number
Bit
Mnemonic
Description
7:0
Low Byte of Timer 0.
Reset Value = 0000 0000b
Table 50. TH1 Register
TH1 (S:8Dh)
Timer 1 High Byte Register
7
6
5
4
3
2
1
0
–
–
–
–
–
–
–
–
Bit Number
Bit
Mnemonic
Description
7:0
High Byte of Timer 1.
Reset Value = 0000 0000b
75
7663E–8051–10/08
Table 51. TL1 Register
TL1 (S:8Bh)
Timer 1 Low Byte Register
7
6
5
4
3
2
1
0
–
–
–
–
–
–
–
–
Bit Number
Bit
Mnemonic
Description
7:0
Low Byte of Timer 1.
Reset Value = 0000 0000b
76
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Timer 2
The Timer 2 in the AT89C51RE2 is the standard C52 Timer 2.
It is a 16-bit timer/counter: the count is maintained by two eight-bit timer registers, TH2 and TL2
are cascaded. It is controlled by T2CON (Table 52) and T2MOD (Table 53) registers. Timer 2
operation is similar to Timer 0 and Timer 1.C/T2 selects FOSC/12 (timer operation) or external pin
T2 (counter operation) as the timer clock input. Setting TR2 allows TL2 to increment by the
selected input.
Timer 2 has 3 operating modes: capture, autoreload and Baud Rate Generator. These modes
are selected by the combination of RCLK, TCLK and CP/RL2 (T2CON).
Refer to the Atmel 8-bit Microcontroller Hardware description for the description of Capture and
Baud Rate Generator Modes.
Timer 2 includes the following enhancements:
•
Auto-reload mode with up or down counter
•
Programmable clock-output
Auto-Reload Mode The auto-reload mode configures Timer 2 as a 16-bit timer or event counter with automatic
reload. If DCEN bit in T2MOD is cleared, Timer 2 behaves as in 80C52 (refer to the Atmel C51
Microcontroller Hardware description). If DCEN bit is set, Timer 2 acts as an Up/down
timer/counter as shown in Figure 28. In this mode the T2EX pin controls the direction of count.
When T2EX is high, Timer 2 counts up. Timer overflow occurs at FFFFh which sets the TF2 flag
and generates an interrupt request. The overflow also causes the 16-bit value in RCAP2H and
RCAP2L registers to be loaded into the timer registers TH2 and TL2.
When T2EX is low, Timer 2 counts down. Timer underflow occurs when the count in the timer
registers TH2 and TL2 equals the value stored in RCAP2H and RCAP2L registers. The underflow sets TF2 flag and reloads FFFFh into the timer registers.
The EXF2 bit toggles when Timer 2 overflows or underflows according to the direction of the
count. EXF2 does not generate any interrupt. This bit can be used to provide 17-bit resolution.
77
7663E–8051–10/08
Figure 28. Auto-Reload Mode Up/Down Counter (DCEN = 1)
FCLK PERIPH
:6
0
1
T2
C/T2
TR2
T2CON
T2CON
T2EX:
(DOWN COUNTING RELOAD VALUE)
if DCEN=1, 1=UP
FFh
FFh
if DCEN=1, 0=DOWN
(8-bit)
(8-bit)
if DCEN = 0, up counting
TOGGLE
T2CON
EXF2
TL2
TH2
(8-bit)
(8-bit)
TIMER 2
INTERRUPT
TF2
T2CON
RCAP2L
(8-bit)
RCAP2H
(8-bit)
(UP COUNTING RELOAD VALUE)
Programmable
Clock-Output
In the clock-out mode, Timer 2 operates as a 50%-duty-cycle, programmable clock generator
(See Figure 29). The input clock increments TL2 at frequency FCLK PERIPH/2.The timer repeatedly
counts to overflow from a loaded value. At overflow, the contents of RCAP2H and RCAP2L registers are loaded into TH2 and TL2.In this mode, Timer 2 overflows do not generate interrupts.
The formula gives the clock-out frequency as a function of the system oscillator frequency and
the value in the RCAP2H and RCAP2L registers:
F CLKPERIPH
Clock – O utFrequency = --------------------------------------------------------------------------------------------4 × ( 65536 – RCAP2H ⁄ RCAP2L )
For a 16 MHz system clock, Timer 2 has a programmable frequency range of 61 Hz
(FCLK PERIPH/216) to 4 MHz (FCLK PERIPH/4). The generated clock signal is brought out to T2 pin
(P1.0).
Timer 2 is programmed for the clock-out mode as follows:
•
Set T2OE bit in T2MOD register.
•
Clear C/T2 bit in T2CON register.
•
Determine the 16-bit reload value from the formula and enter it in RCAP2H/RCAP2L
registers.
•
Enter a 16-bit initial value in timer registers TH2/TL2.It can be the same as the reload value
or a different one depending on the application.
•
To start the timer, set TR2 run control bit in T2CON register.
It is possible to use Timer 2 as a baud rate generator and a clock generator simultaneously. For
this configuration, the baud rates and clock frequencies are not independent since both functions use the values in the RCAP2H and RCAP2L registers.
78
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Figure 29. Clock-Out Mode C/T2 = 0
FCLK PERIPH
:6
TR2
T2CON
TL2
(8-bit)
TH2
(8-bit)
OVERFLOW
RCAP2L RCAP2H
(8-bit) (8-bit)
Toggle
T2
Q
D
T2OE
T2MOD
T2EX
EXF2
EXEN2
T2CON
T2CON
TIMER 2
INTERRUPT
79
7663E–8051–10/08
Registers
Table 52. T2CON Register
T2CON - Timer 2 Control Register (C8h)
7
6
5
4
3
2
1
0
TF2
EXF2
RCLK
TCLK
EXEN2
TR2
C/T2#
CP/RL2#
Bit
Bit
Number
Mnemonic
7
TF2
Description
Timer 2 overflow Flag
Must be cleared by software.
Set by hardware on Timer 2 overflow, if RCLK = 0 and TCLK = 0.
6
EXF2
Timer 2 External Flag
Set when a capture or a reload is caused by a negative transition on T2EX pin if
EXEN2=1.
When set, causes the CPU to vector to Timer 2 interrupt routine when Timer 2 interrupt
is enabled.
Must be cleared by software. EXF2 doesn’t cause an interrupt in Up/down counter mode
(DCEN = 1).
5
RCLK
Receive Clock bit
Cleared to use timer 1 overflow as receive clock for serial port in mode 1 or 3.
Set to use Timer 2 overflow as receive clock for serial port in mode 1 or 3.
4
TCLK
Transmit Clock bit
Cleared to use timer 1 overflow as transmit clock for serial port in mode 1 or 3.
Set to use Timer 2 overflow as transmit clock for serial port in mode 1 or 3.
3
EXEN2
2
TR2
1
0
C/T2#
CP/RL2#
Timer 2 External Enable bit
Cleared to ignore events on T2EX pin for Timer 2 operation.
Set to cause a capture or reload when a negative transition on T2EX pin is detected, if
Timer 2 is not used to clock the serial port.
Timer 2 Run control bit
Cleared to turn off Timer 2.
Set to turn on Timer 2.
Timer/Counter 2 select bit
Cleared for timer operation (input from internal clock system: FCLK PERIPH).
Set for counter operation (input from T2 input pin, falling edge trigger). Must be 0 for
clock out mode.
Timer 2 Capture/Reload bit
If RCLK=1 or TCLK=1, CP/RL2# is ignored and timer is forced to auto-reload on Timer 2
overflow.
Cleared to auto-reload on Timer 2 overflows or negative transitions on T2EX pin if
EXEN2=1.
Set to capture on negative transitions on T2EX pin if EXEN2=1.
Reset Value = 0000 0000b
Bit addressable
80
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 53. T2MOD Register
T2MOD - Timer 2 Mode Control Register (C9h)
7
6
5
4
3
2
1
0
-
-
-
-
-
-
T2OE
DCEN
Bit
Bit
Number
Mnemonic
7
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
6
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
5
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
4
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
3
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
2
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
1
T2OE
Timer 2 Output Enable bit
Cleared to program P1.0/T2 as clock input or I/O port.
Set to program P1.0/T2 as clock output.
0
DCEN
Down Counter Enable bit
Cleared to disable Timer 2 as up/down counter.
Set to enable Timer 2 as up/down counter.
Description
Reset Value = XXXX XX00b
Not bit addressable
81
7663E–8051–10/08
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 (FCLK PERIPH)
÷6
•
Peripheral clock frequency (FCLK PERIPH) ÷ 2
•
Timer 0 overflow
•
External input on ECI (P1.2)
Each compare/capture modules 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 Section "PCA Watchdog Timer",
page 93).
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 the port is not used for the PCA, it can still be used for standard I/O.
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
The PCA timer is a common time base for all five modules (See Figure 30). The timer count
source is determined from the CPS1 and CPS0 bits in the CMOD register (Table 54) and can be
programmed to run at:
82
•
1/6 the peripheral clock frequency (FCLK PERIPH)
•
1/2 the peripheral clock frequency (FCLK PERIPH)
•
The Timer 0 overflow
•
The input on the ECI pin (P1.2)
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Figure 30. PCA Timer/Counter
To PCA
modules
Fclk periph /6
overflow
Fclk periph / 2
CH
T0 OVF
It
CL
16 bit up/down counter
P1.2
CIDL
WDTE
CF
CR
CPS1
CPS0
ECF
CMOD
0xD9
CCF2
CCF1
CCF0
CCON
0xD8
Idle
CCF4 CCF3
83
7663E–8051–10/08
Table 54. CMOD Register
CMOD - PCA Counter Mode Register (D9h)
7
6
5
4
3
2
1
0
CIDL
WDTE
-
-
-
CPS1
CPS0
ECF
Bit
Bit
Number
Mnemonic
7
CIDL
Description
Counter Idle Control
Cleared to program the PCA Counter to continue functioning during idle Mode.
Set to program PCA to be gated off during idle.
Watchdog Timer Enable
6
WDTE
Cleared to disable Watchdog Timer function on PCA Module 4.
Set to enable Watchdog Timer function on PCA Module 4.
5
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
4
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
3
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
2
CPS1
PCA Count Pulse Select
CPS1 CPS0 Selected PCA input
0
0
Internal clock fCLK PERIPH/6
1
0
CPS0
ECF
0
1
1
0
Internal clock fCLK PERIPH/2
Timer 0 Overflow
1
1
External clock at ECI/P1.2 pin (max rate = fCLK PERIPH/ 4)
PCA Enable Counter Overflow Interrupt
Cleared to disable CF bit in CCON to inhibit an interrupt.
Set to enable CF bit in CCON to generate an interrupt.
Reset Value = 00XX X000b
Not bit addressable
The CMOD register includes three additional bits associated with the PCA (See Figure 30 and
Table 54).
•
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.
•
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.
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 55).
84
•
Bit CR (CCON.6) must be set by software to run the PCA. The PCA is shut off by clearing
this bit.
•
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.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 55. CCON Register
CCON - PCA Counter Control Register (D8h)
7
6
5
4
3
2
1
0
CF
CR
-
CCF4
CCF3
CCF2
CCF1
CCF0
Bit
Bit
Number
Mnemonic
Description
PCA Counter Overflow flag
7
CF
Set by hardware when the counter rolls over. CF flags an interrupt if bit ECF in CMOD is
set. CF
may be set by either hardware or software but can only be cleared by software.
PCA Counter Run control bit
6
CR
Must be cleared by software to turn the PCA counter off.
Set by software to turn the PCA counter on.
5
-
4
CCF4
Reserved
The value read from this bit is indeterminate. Do not set this bit.
PCA Module 4 interrupt flag
Must be cleared by software.
Set by hardware when a match or capture occurs.
PCA Module 3 interrupt flag
3
CCF3
Must be cleared by software.
Set by hardware when a match or capture occurs.
PCA Module 2 interrupt flag
2
CCF2
Must be cleared by software.
Set by hardware when a match or capture occurs.
PCA Module 1 interrupt flag
1
CCF1
Must be cleared by software.
Set by hardware when a match or capture occurs.
PCA Module 0 interrupt flag
0
CCF0
Must be cleared by software.
Set by hardware when a match or capture occurs.
Reset Value = 00X0 0000b
Not bit addressable
The watchdog timer function is implemented in module 4 (See Figure 33).
The PCA interrupt system is shown in Figure 31.
85
7663E–8051–10/08
Figure 31. PCA Interrupt System
CF
CR
CCF4 CCF3 CCF2 CCF1 CCF0
CCON
0xD8
PCA Timer/Counter
Module 0
Module 1
To Interrupt
priority decoder
Module 2
Module 3
Module 4
CMOD.0
ECF
ECCFn CCAPMn.0
IE.6
EC
IE.7
EA
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 56). 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.
•
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 module's 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 module's 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 56 shows the CCAPMn settings for the various PCA functions.
86
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 56. CCAPMn Registers (n = 0-4)
CCAPM0 - PCA Module 0 Compare/Capture Control Register (0DAh)
CCAPM1 - PCA Module 1 Compare/Capture Control Register (0DBh)
CCAPM2 - PCA Module 2 Compare/Capture Control Register (0DCh)
CCAPM3 - PCA Module 3 Compare/Capture Control Register (0DDh)
CCAPM4 - PCA Module 4 Compare/Capture Control Register (0DEh)
7
6
5
4
3
2
1
0
-
ECOMn
CAPPn
CAPNn
MATn
TOGn
PWMn
ECCFn
Bit
Bit
Number
Mnemonic
7
-
6
ECOMn
Description
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Enable Comparator
Cleared to disable the comparator function.
Set to enable the comparator function.
Capture Positive
5
CAPPn
4
CAPNn
Cleared to disable positive edge capture.
Set to enable positive edge capture.
Capture Negative
Cleared to disable negative edge capture.
Set to enable negative edge capture.
Match
3
MATn
When MATn = 1, a match of the PCA counter with this module's compare/capture
register causes the
CCFn bit in CCON to be set, flagging an interrupt.
Toggle
2
TOGn
When TOGn = 1, a match of the PCA counter with this module's compare/capture
register causes the
CEXn pin to toggle.
Pulse Width Modulation Mode
1
PWMn
Cleared to disable the CEXn pin to be used as a pulse width modulated output.
Set to enable the CEXn pin to be used as a pulse width modulated output.
Enable CCF interrupt
0
CCF0
Cleared to disable compare/capture flag CCFn in the CCON register to generate an
interrupt.
Set to enable compare/capture flag CCFn in the CCON register to generate an interrupt.
Reset Value = X000 0000b
Not bit addressable
87
7663E–8051–10/08
Table 57. PCA Module Modes (CCAPMn Registers)
ECOMn
CAPPn
CAPNn
MATn
TOGn
PWMm
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 58 & Table 59).
Table 58. CCAPnH Registers (n = 0-4)
CCAP0H - PCA Module 0 Compare/Capture Control Register High (0FAh)
CCAP1H - PCA Module 1 Compare/Capture Control Register High (0FBh)
CCAP2H - PCA Module 2 Compare/Capture Control Register High (0FCh)
CCAP3H - PCA Module 3 Compare/Capture Control Register High (0FDh)
CCAP4H - PCA Module 4 Compare/Capture Control Register High (0FEh)
7
6
5
4
3
2
1
0
-
-
-
-
-
-
-
-
Bit
Bit
Number
Mnemonic
7-0
-
Description
PCA Module n Compare/Capture Control
CCAPnH Value
Reset Value = 0000 0000b
Not bit addressable
88
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 59. CCAPnL Registers (n = 0-4)
CCAP0L - PCA Module 0 Compare/Capture Control Register Low (0EAh)
CCAP1L - PCA Module 1 Compare/Capture Control Register Low (0EBh)
CCAP2L - PCA Module 2 Compare/Capture Control Register Low (0ECh)
CCAP3L - PCA Module 3 Compare/Capture Control Register Low (0EDh)
CCAP4L - PCA Module 4 Compare/Capture Control Register Low (0EEh)
7
6
5
4
3
2
1
0
-
-
-
-
-
-
-
-
Bit
Bit
Number
Mnemonic
7-0
-
Description
PCA Module n Compare/Capture Control
CCAPnL Value
Reset Value = 0000 0000b
Not bit addressable
Table 60. CH Register
CH - PCA Counter Register High (0F9h)
7
6
5
4
3
2
1
0
-
-
-
-
-
-
-
-
Bit
Bit
Number
Mnemonic
7-0
-
Description
PCA counter
CH Value
Reset Value = 0000 0000b
Not bit addressable
Table 61. CL Register
CL - PCA Counter Register Low (0E9h)
7
6
5
4
3
2
1
0
-
-
-
-
-
-
-
-
Bit
Bit
Number
Mnemonic
7-0
-
Description
PCA Counter
CL Value
Reset Value = 0000 0000b
Not bit addressable
89
7663E–8051–10/08
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 32).
Figure 32. PCA Capture Mode
CF
CR
CCF4 CCF3 CCF2
CCF1 CCF0 CCON
0xD8
PCA IT
PCA Counter/Timer
Cex.n
CH
CL
CCAPnH
CCAPnL
Capture
ECOMn CAPPn CAPNn MATn TOGn PWMn ECCFn CCAPMn, n= 0 to 4
0xDA to 0xDE
16-bit Software
Timer/ Compare
Mode
90
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 33).
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Figure 33. PCA Compare Mode and PCA Watchdog Timer
CCON
CF
Write to
CCAPnL
CR
CCF4 CCF3 CCF2 CCF1 CCF0
0xD8
Reset
PCA IT
Write to
CCAPnH
1
CCAPnH
0
CCAPnL
Enable
Match
16 bit comparator
CH
RESET *
CL
PCA counter/timer
ECOMn CAPPn CAPNn MATn TOGn PWMn ECCFn
CIDL
WDTE
CPS1 CPS0
ECF
CCAPMn, n = 0 to 4
0xDA to 0xDE
CMOD
0xD9
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 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.
High Speed Output 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 module's capture registers. To activate this
Mode
mode the TOG, MAT, and ECOM bits in the module's CCAPMn SFR must be set (See
Figure 34).
A prior write must be done to CCAPnL and CCAPnH before writing the ECOMn bit.
91
7663E–8051–10/08
Figure 34. PCA High Speed Output Mode
CCON
CF
CR
CCF4 CCF3 CCF2 CCF1 CCF0
0xD8
Write to
CCA PnL Reset
PCA IT
Write to
CCAPnH
1
CCAPnH
0
CCAPnL
Enable
16 bit comparator
CH
Match
CL
CEXn
PCA counter/timer
ECO Mn CAPPn CAPNn MATn TOGn PWMn ECCFn
CCAPMn, n = 0 to 4
0xDA to 0xDE
Before enabling ECOM bit, CCAPnL and CCAPnH should be set with a non zero value, otherwise an unwanted match could happen.
Once ECOM 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.
Pulse Width
Modulator Mode
92
All of the PCA modules can be used as PWM outputs. Figure 35 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 module's capture register CCAPLn. When the value
of the PCA CL SFR is less than the value in the module's CCAPLn SFR the output will be low,
when it is equal to or greater than the output will be high. When CL overflows from FF to 00,
CCAPLn is reloaded with the value in CCAPHn. 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.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Figure 35. PCA PWM Mode
CCAPnH
Overflow
CCAPnL
“0”
CEXn
Enable
8 bit comparator
“1”
CL
PCA counter/timer
ECOMn CAPPn CAPNn MATn TOGn PWMn ECCFn
CCAPMn, n= 0 to 4
0xDA to 0xDE
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 33 shows a diagram of how the watchdog works. The user preloads 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 will not cause the RST pin to be driven high.
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, or
3. disable the watchdog by clearing the WDTE bit before a match occurs and then re-enable 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.
93
7663E–8051–10/08
Serial I/O Port
The serial I/O ports in the AT89C51RE2 are compatible with the serial I/O port in the 80C52.
They provide both synchronous and asynchronous communication modes. They operates as a
Universal Asynchronous Receiver and Transmitter (UART) in three full-duplex modes (Modes 1,
2 and 3). Asynchronous transmission and reception can occur simultaneously and at different
baud rates
Both serial I/O port include the following enhancements:
•
Framing error detection
•
Automatic address recognition
As these improvements apply to both UART, most of the time in the following lines, there won’t
be any reference to UART_0 or UART_1, but only to UART, generally speaking.
Framing Error
Detection
Framing bit error detection is provided for the three asynchronous modes (modes 1, 2 and 3). To
enable the framing bit error detection feature, set SMOD0 bit in PCON register (See Figure 36)
for UART 0 or set SMOD0_1 in BDRCON_1 register for UART 1 (See Figure 37).
Figure 36. UART 0 Framing Error Block Diagram
SM0/FE
SM1
SM2
REN
TB8
RB8
TI
RI
SCON_0 (98h)
Set FE bit if stop bit is 0 (framing error) (SMOD0 = 1)
SM0 to UART 0 mode control (SMOD0 = 0)
SM0D1
SMOD0
-
POF
GF1
GF0
PD
IDL
PCON (87h)
TI_1
RI_1
SCON_1 (C0h)
To UART 0 framing error control
Figure 37. UART 1 Framing Error Block Diagram
SM0_1/FE_1
SM1_1
SM2_1
REN_1
TB8_1
RB8_1
Set FE_1 bit if stop bit is 0 (framing error) (SMOD0_1 = 1)
SM0 to UART 1 mode control (SMOD0_1 = 0)
SM0D1_1SMOD0_1
-
BRR_1
TBCK_1 RBCK_1
SPD_1
SRC_1
BDRCON_1 (87h)
To UART 1 framing error control
When this feature is enabled, the receiver checks each incoming data frame for a valid stop bit.
An invalid stop bit may result from noise on the serial lines or from simultaneous transmission by
two CPUs. If a valid stop bit is not found, the Framing Error bit (FE) in SCON register (See Table
68.) bit is set.
Software may examine FE bit after each reception to check for data errors. Once set, only software or a reset can clear FE bit. Subsequently received frames with valid stop bits cannot clear
FE bit. When FE feature is enabled, RI rises on stop bit instead of the last data bit (See
Figure 38 and Figure 39).
94
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Figure 38. UART Timings in Mode 1
RXD
D0
D1
D2
D3
D4
D5
D6
D7
Data byte
Start
bit
Stop
bit
RI
SMOD0=X
FE
SMOD0=1
Figure 39. UART Timings in Modes 2 and 3
RXD
D0
Start
bit
D1
D2
D3
D4
Data byte
D5
D6
D7
D8
Ninth Stop
bit
bit
RI
SMOD0=0
RI
SMOD0=1
FE
SMOD0=1
Automatic
Address
Recognition
The automatic address recognition feature is enabled when the multiprocessor communication
feature is enabled (SM2 bit in SCON register is set).
Implemented in hardware, automatic address recognition enhances the multiprocessor communication feature by allowing the serial port to examine the address of each incoming command
frame. Only when the serial port recognizes its own address, the receiver sets RI bit in SCON
register to generate an interrupt. This ensures that the CPU is not interrupted by command
frames addressed to other devices.
If desired, the user may enable the automatic address recognition feature in mode 1.In this configuration, the stop bit takes the place of the ninth data bit. Bit RI is set only when the received
command frame address matches the device’s address and is terminated by a valid stop bit.
To support automatic address recognition, a device is identified by a given address and a broadcast address.
Note:
Given Address
The multiprocessor communication and automatic address recognition features cannot be
enabled in mode 0 (i. e. setting SM2 bit in SCON register in mode 0 has no effect).
Each device has an individual address that is specified in SADDR register; the SADEN register
is a mask byte that contains don’t-care bits (defined by zeros) to form the device’s given
address. The don’t-care bits provide the flexibility to address one or more slaves at a time. The
following example illustrates how a given address is formed.
To address a device by its individual address, the SADEN mask byte must be 1111 1111b.
For example:
SADDR0101 0110b
SADEN1111 1100b
Given0101 01XXb
The following is an example of how to use given addresses to address different slaves:
95
7663E–8051–10/08
Slave A:SADDR1111 0001b
SADEN1111 1010b
Given1111 0X0Xb
Slave B:SADDR1111 0011b
SADEN1111 1001b
Given1111 0XX1b
Slave C:SADDR1111 0010b
SADEN1111 1101b
Given1111 00X1b
The SADEN byte is selected so that each slave may be addressed separately.
For slave A, bit 0 (the LSB) is a don’t-care bit; for slaves B and C, bit 0 is a 1.To communicate
with slave A only, the master must send an address where bit 0 is clear (e.g.. 1111 0000b).
For slave A, bit 1 is a 1; for slaves B and C, bit 1 is a don’t care bit. To communicate with slaves
B and C, but not slave A, the master must send an address with bits 0 and 1 both set (e.g. 1111
0011b).
To communicate with slaves A, B and C, the master must send an address with bit 0 set, bit 1
clear, and bit 2 clear (e.g. 1111 0001b).
Broadcast Address
A broadcast address is formed from the logical OR of the SADDR and SADEN registers with
zeros defined as don’t-care bits, e.g.:
SADDR0101 0110b
SADEN1111 1100b
Broadcast =SADDR OR SADEN1111 111Xb
The use of don’t-care bits provides flexibility in defining the broadcast address, however in most
applications, a broadcast address is FFh. The following is an example of using broadcast
addresses:
Slave A:SADDR1111 0001b
SADEN1111 1010b
Broadcast1111 1X11b,
Slave B:SADDR1111 0011b
SADEN1111 1001b
Broadcast1111 1X11B,
Slave C:SADDR=1111 0011b
SADEN1111 1101b
Broadcast1111 1111b
For slaves A and B, bit 2 is a don’t care bit; for slave C, bit 2 is set. To communicate with all of
the slaves, the master must send an address FFh. To communicate with slaves A and B, but not
slave C, the master can send and address FBh.
Reset Addresses
96
On reset, the SADDR and SADEN registers are initialized to 00h, i. e. the given and broadcast
addresses are XXXX XXXXb (all don’t-care bits). This ensures that the serial port will reply to any
address, and so, that it is backwards compatible with the 80C51 microcontrollers that do not
support automatic address recognition.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Registers
Table 62. SADEN_0 Register
SADEN - Slave Address Mask Register UART 0(B9h)
7
6
5
4
3
2
1
0
3
2
1
0
3
2
1
0
3
2
1
0
Reset Value = 0000 0000b
Not bit addressable
Table 63. SADDR_0 Register
SADDR - Slave Address Register UART 0(A9h)
7
6
5
4
Reset Value = 0000 0000b
Not bit addressable
Table 64. SADEN_1 Register
SADEN_1 - Slave Address Mask Register UART 1(BAh)
7
6
5
4
Reset Value = 0000 0000b
Not bit addressable
Table 65. SADDR_1 Register
SADDR_1 - Slave Address Register UART 1(AAh)
7
6
5
4
Reset Value = 0000 0000b
Not bit addressable
97
7663E–8051–10/08
Baud Rate
The Baud Rate Generator for transmit and receive clocks can be selected separately via the
T2CON and BDRCON_0 registers.
Selection for
UART 0 for Mode 1
Figure 40. Baud Rate Selection for UART 0
and 3
TIMER1
0
TIMER2
TIMER_BRG_RX
0
1
/ 16
Rx Clock_0
1
RCLK
RBCK
INT_BRG
TIMER1
0
TIMER2
TIMER_BRG_TX
0
1
/ 16
1
Tx Clock_0
TCLK
TBCK
INT_BRG
Table 66. Baud Rate Selection Table UART 0
98
TCLK
RCLK
TBCK
RBCK
Clock Source
Clock Source
(T2CON)
(T2CON)
(BDRCON)
(BDRCON)
UART Tx
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
INT_BRG
Timer 1
X
1
1
0
INT_BRG
Timer 2
0
X
0
1
Timer 1
INT_BRG
1
X
0
1
Timer 2
INT_BRG
X
X
1
1
INT_BRG
INT_BRG
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Baud Rate
The Baud Rate Generator for transmit and receive clocks can be selected separately via the
T2CON and BDRCON_1 registers.
Selection for
UART 1 for Mode 1
Figure 41. Baud Rate Selection for UART 1
and 3
TIMER1
0
TIMER2
TIMER_BRG_RX
0
1
/ 16
Rx Clock_1
1
RCLK
RBCK_1
INT_BRG1
TIMER1
0
TIMER2
TIMER_BRG_TX
0
1
/ 16
1
Tx Clock_1
TCLK
TBCK_1
INT_BRG1
Table 67. Baud Rate Selection Table UART 1
TCLK
RCLK
TBCK_1
RBCK_1
Clock Source
Clock Source
(T2CON)
(T2CON)
(BDRCON_1)
(BDRCON_1)
UART Tx_1
UART Rx_1
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
INT_BRG_1
Timer 1
X
1
1
0
INT_BRG_1
Timer 2
0
X
0
1
Timer 1
INT_BRG_1
1
X
0
1
Timer 2
INT_BRG_1
X
X
1
1
INT_BRG_1
INT_BRG_1
99
7663E–8051–10/08
Internal Baud Rate
Generator (BRG)
The AT89C51RE2 implements two internal baudrate generators. Each one is dedicated to the
corresponding UART. The configuration and operating mode for both BRG are similar. When an
internal Baud Rate Generator is used, the Baud Rates are determined by the BRG overflow
depending on the BRL (BRL or BRL_1 registers) reload value, the value of SPD (or SPD_1) bit
(Speed Mode) in BDRCON (BDRCON_1) register and the value of the SMOD1 bit in PCON
register.
Figure 42. Internal Baud Rate generator 0
FPER
/6
0
auto reload counter
overflow
BRG
/2
0
1
INT_BRG
1
SPD_0
BRL_0
0
auto reload counter
overflow
BRG
SMOD1
BRR_0
Figure 43. Internal Baud Rate generator 1
FPER
/6
1
SPD_1
/2
0
INT_BRG1
1
BRL_1
SMOD1_1
BRR_1
•
The baud rate for UART is token by formula:
Baud_Rate =
BRL = 256 -
100
2SMOD1 ⋅ FPER
6(1-SPD) ⋅ 32 ⋅ (256 -BRL)
2SMOD1 ⋅ FPER
⋅ 32 ⋅ Baud_Rate
(1-SPD)
6
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 68. SCON_0 register
SCON_0 - Serial Control Register for UART 0(98h)
7
6
5
4
3
2
1
0
FE/SM0_0
SM1_0
SM2_0
REN_0
TB8_0
RB8_0
TI_0
RI_0
Bit
Bit
Number
Mnemonic
Description
Framing Error bit (SMOD0=1)
FE_0
Clear to reset the error state, not cleared by a valid stop bit.
Set by hardware when an invalid stop bit is detected.
SMOD0 must be set to enable access to the FE bit.
7
SM0_0
Serial port Mode bit 0
Refer to SM1_0 for serial port mode selection.
SMOD0_0 must be cleared to enable access to the SM0_0 bit.
6
SM1_0
Serial port Mode bit 1
SM0 SM1 Mode Description
Baud Rate
0
0
1
0
1
0
0
1
2
Shift Register
8-bit UART
9-bit UART
FCPU PERIPH/6
Variable
FCPU PERIPH /32 or /16
1
1
3
9-bit UART
Variable
Serial port Mode 2 bit / Multiprocessor Communication Enable bit
5
SM2_0
4
REN_0
3
TB8_0
Clear to disable multiprocessor communication feature.
Set to enable multiprocessor communication feature in mode 2 and 3, and
eventually mode 1.This bit should be cleared in mode 0.
Reception Enable bit
Clear to disable serial reception.
Set to enable serial reception.
Transmitter Bit 8 / Ninth bit to transmit in modes 2 and 3
2
RB8_0
Clear to transmit a logic 0 in the 9th bit.
Set to transmit a logic 1 in the 9th bit.
Receiver Bit 8 / Ninth bit received in modes 2 and 3
Cleared by hardware if 9th bit received is a logic 0.
Set by hardware if 9th bit received is a logic 1.
In mode 1, if SM2_0 = 0, RB8 is the received stop bit. In mode 0 RB8 is not used.
1
0
TI_0
Transmit Interrupt flag
Clear to acknowledge interrupt.
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.
RI_0
Receive Interrupt flag
Clear to acknowledge interrupt.
Set by hardware at the end of the 8th bit time in mode 0, see Figure 38. and
Figure 39. in the other modes.
Reset Value = 0000 0000b
Bit addressable
101
7663E–8051–10/08
Table 69. SCON_1 Register
SCON_1 - Serial Control Register for UART 1(C0h)
7
6
5
4
3
2
1
0
FE/SM0_1
SM1_1
SM2_1
REN_1
TB8_1
RB8_1
TI_1
RI_1
Bit
Bit
Number
Mnemonic
Description
Framing Error bit (SMOD0=1)
FE_1
Clear to reset the error state, not cleared by a valid stop bit.
Set by hardware when an invalid stop bit is detected.
SMOD0_1 must be set to enable access to the FE_1 bit.
7
SM0_1
Serial port Mode bit 0
Refer to SM1_1 for serial port mode selection.
SMOD0_1 must be cleared to enable access to the SM0_1 bit.
6
SM1_1
Serial port Mode bit 1
SM0 SM1 Mode Description
Baud Rate
0
0
1
0
1
0
0
1
2
Shift Register
8-bit UART
9-bit UART
FCPU PERIPH/6
Variable
FCPU PERIPH /32 or /16
1
1
3
9-bit UART
Variable
Serial port Mode 2 bit / Multiprocessor Communication Enable bit
5
SM2_1
4
REN_1
3
TB8_1
Clear to disable multiprocessor communication feature.
Set to enable multiprocessor communication feature in mode 2 and 3, and
eventually mode 1.This bit should be cleared in mode 0.
Reception Enable bit
Clear to disable serial reception.
Set to enable serial reception.
Transmitter Bit 8 / Ninth bit to transmit in modes 2 and 3
2
RB8_1
Clear to transmit a logic 0 in the 9th bit.
Set to transmit a logic 1 in the 9th bit.
Receiver Bit 8 / Ninth bit received in modes 2 and 3
Cleared by hardware if 9th bit received is a logic 0.
Set by hardware if 9th bit received is a logic 1.
In mode 1, if SM2_1 = 0, RB8 is the received stop bit. In mode 0 RB8 is not used.
1
0
TI_1
Transmit Interrupt flag
Clear to acknowledge interrupt.
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.
RI_1
Receive Interrupt flag
Clear to acknowledge interrupt.
Set by hardware at the end of the 8th bit time in mode 0, see Figure 38. and
Figure 39. in the other modes.
Reset Value = 0000 0000b
Bit addressable
102
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 70. Example of Computed Value When X2=1, SMOD1=1, SPD=1
Baud Rates
FOSC = 16. 384 MHz
FOSC = 24MHz
BRL
Error (%)
BRL
Error (%)
115200
247
1.23
243
0.16
57600
238
1.23
230
0.16
38400
229
1.23
217
0.16
28800
220
1.23
204
0.16
19200
203
0.63
178
0.16
9600
149
0.31
100
0.16
4800
43
1.23
-
-
Table 71. Example of Computed Value When X2=0, SMOD1=0, SPD=0
Baud Rates
FOSC = 16. 384 MHz
FOSC = 24MHz
BRL
Error (%)
BRL
Error (%)
4800
247
1.23
243
0.16
2400
238
1.23
230
0.16
1200
220
1.23
202
3.55
600
185
0.16
152
0.16
The baud rate generator can be used for mode 1 or 3 (refer to Figure 40.), but also for mode 0
for UART, thanks to the bit SRC located in BDRCON register (Table 78.)
UART Registers
Table 72. SBUF_0 register
SBUF_0 - Serial Buffer Register for UART 0(99h)
7
6
5
4
3
2
1
0
Reset Value = XXXX XXXXb
Table 73. BRL_0 register
BRL_0 - Baud Rate Reload Register for the internal baud rate generator 0 (9Ah)
7
6
5
4
3
2
1
0
Reset Value = 0000 0000b
103
7663E–8051–10/08
Table 74. SBUF_1 Register
SBUF - Serial Buffer Register for UART 1(C1h)
7
6
5
4
3
2
1
0
Reset Value = XXXX XXXXb
Table 75. BRL_1 Register
BRL - Baud Rate Reload Register for the internal baud rate generator 1 (BBh)
7
6
5
4
3
2
1
0
Reset Value = 0000 0000b
104
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 76. T2CON Register
T2CON - Timer 2 Control Register (C8h)
7
6
5
4
3
2
1
0
TF2
EXF2
RCLK
TCLK
EXEN2
TR2
C/T2#
CP/RL2#
Bit
Bit
Number
Mnemonic
7
TF2
Description
Timer 2 overflow Flag
Must be cleared by software.
Set by hardware on timer 2 overflow, if RCLK = 0 and TCLK = 0.
6
EXF2
Timer 2 External Flag
Set when a capture or a reload is caused by a negative transition on T2EX pin if
EXEN2=1.
When set, causes the CPU to vector to timer 2 interrupt routine when timer 2 interrupt is
enabled.
Must be cleared by software. EXF2 doesn’t cause an interrupt in Up/down counter
mode (DCEN = 1)
5
RCLK
Receive Clock bit for UART
Cleared to use timer 1 overflow as receive clock for serial port in mode 1 or 3.
Set to use timer 2 overflow as receive clock for serial port in mode 1 or 3.
4
TCLK
Transmit Clock bit for UART
Cleared to use timer 1 overflow as transmit clock for serial port in mode 1 or 3.
Set to use timer 2 overflow as transmit clock for serial port in mode 1 or 3.
3
EXEN2
2
TR2
1
0
C/T2#
CP/RL2#
Timer 2 External Enable bit
Cleared to ignore events on T2EX pin for timer 2 operation.
Set to cause a capture or reload when a negative transition on T2EX pin is detected, if
timer 2 is not used to clock the serial port.
Timer 2 Run control bit
Cleared to turn off timer 2.
Set to turn on timer 2.
Timer/Counter 2 select bit
Cleared for timer operation (input from internal clock system: FCLK PERIPH).
Set for counter operation (input from T2 input pin, falling edge trigger). Must be 0 for
clock out mode.
Timer 2 Capture/Reload bit
If RCLK=1 or TCLK=1, CP/RL2# is ignored and timer is forced to auto-reload on timer 2
overflow.
Cleared to auto-reload on timer 2 overflows or negative transitions on T2EX pin if
EXEN2=1.
Set to capture on negative transitions on T2EX pin if EXEN2=1.
Reset Value = 0000 0000b
Bit addressable
105
7663E–8051–10/08
Table 77. PCON Register
PCON - Power Control Register (87h)
7
6
5
4
3
2
1
0
SMOD1_0
SMOD0_0
-
POF
GF1
GF0
PD
IDL
Bit
Bit
Number
Mnemonic
7
SMOD1_0
6
SMOD0_0
5
-
Description
Serial port Mode bit 1 for UART
Set to select double baud rate in mode 1, 2 or 3.
Serial port Mode bit 0 for UART
Cleared to select SM0 bit in SCON register.
Set to select FE bit in SCON register.
Reserved
The value read from this bit is indeterminate. Do not set this bit.
4
POF
Power-Off Flag
Cleared to recognize next reset type.
Set by hardware when VCC rises from 0 to its nominal voltage. Can also be set by
software.
3
GF1
General purpose Flag
Cleared by user for general purpose usage.
Set by user for general purpose usage.
2
GF0
General purpose Flag
Cleared by user for general purpose usage.
Set by user for general purpose usage.
1
PD
Power-Down mode bit
Cleared by hardware when reset occurs.
Set to enter power-down mode.
0
IDL
Idle mode bit
Cleared by hardware when interrupt or reset occurs.
Set to enter idle mode.
Reset Value = 00X1 0000b
Not bit addressable
Power-off flag reset value will be 1 only after a power on (cold reset). A warm reset doesn’t affect
the value of this bit.
106
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 78. BDRCON_0 Register
BDRCON_0 - Baud Rate Control Register (9Bh)
7
6
5
4
3
2
1
0
-
-
-
BRR_0
TBCK_0
RBCK_0
SPD_0
SRC_0
Bit
Number
Bit
Mnemonic
7
-
Reserved
The value read from this bit is indeterminate. Do not set this bit
6
-
Reserved
The value read from this bit is indeterminate. Do not set this bit
5
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
4
BRR_0
Baud Rate Run Control bit
Cleared to stop the internal Baud Rate Generator.
Set to start the internal Baud Rate Generator.
3
TBCK_0
Transmission Baud rate Generator Selection bit for UART
Cleared to select Timer 1 or Timer 2 for the Baud Rate Generator.
Set to select internal Baud Rate Generator.
2
RBCK_0
Reception Baud Rate Generator Selection bit for UART
Cleared to select Timer 1 or Timer 2 for the Baud Rate Generator.
Set to select internal Baud Rate Generator.
1
SPD_0
0
SRC_0
Description
Baud Rate Speed Control bit for UART
Cleared to select the SLOW Baud Rate Generator.
Set to select the FAST Baud Rate Generator.
Baud Rate Source select bit in Mode 0 for UART
Cleared to select FOSC/12 as the Baud Rate Generator (FCLK PERIPH/6 in X2 mode).
Set to select the internal Baud Rate Generator for UARTs in mode 0.
Reset Value = XXX0 0000b
Not bit addressable
107
7663E–8051–10/08
Table 79. BDRCON_1 Register
BDRCON - Baud Rate Control Register (BCh)
7
6
5
4
3
2
1
0
SMOD1_1
SMOD0_1
-
BRR_1
TBCK_1
RBCK_1
SPD_1
SRC_1
Bit
Number
Bit
Mnemonic
7
SMOD1_1
6
SMOD0_1
5
-
4
BRR_1
Baud Rate Run Control bit
Cleared to stop the internal Baud Rate Generator.
Set to start the internal Baud Rate Generator.
3
TBCK_1
Transmission Baud rate Generator Selection bit for UART 1
Cleared to select Timer 1 or Timer 2 for the Baud Rate Generator.
Set to select internal Baud Rate Generator.
2
RBCK_1
Reception Baud Rate Generator Selection bit for UART 1
Cleared to select Timer 1 or Timer 2 for the Baud Rate Generator.
Set to select internal Baud Rate Generator.
1
SPD_1
0
SRC_1
Description
Serial port Mode bit 1 for UART 1
Set to select double baud rate in mode 1, 2 or 3.
Serial port Mode bit 0 for UART 1
Cleared to select SM0 bit in SCON register.
Set to select FE bit in SCON register.
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Baud Rate Speed Control bit for UART 1
Cleared to select the SLOW Baud Rate Generator.
Set to select the FAST Baud Rate Generator.
Baud Rate Source select bit in Mode 0 for UART 1
Cleared to select FOSC/12 as the Baud Rate Generator (FCLK PERIPH/6 in X2 mode).
Set to select the internal Baud Rate Generator for UARTs in mode 0.
Reset Value = 0000 0000b
Not bit addressable
108
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Interrupt
System
The AT89C51RE2 has a total of 10 interrupt vectors: two external interrupts (INT0 and INT1),
three timer interrupts (timers 0, 1 and 2), two serial ports interrupts, SPI interrupt, Keyboard
interrupt and the PCA global interrupt. These interrupts are shown in Figure 44.
Figure 44. Interrupt Control System
High priority
interrupt
IPH, IPL
3
INT0
IE0
0
3
TF0
0
3
INT1
IE1
0
3
Interrupt
polling
sequence, decreasing from
high to low priority
TF1
0
3
PCA IT
0
RI
TI
3
TF2
EXF2
3
0
0
3
KBD IT
0
3
TWI IT
0
3
SPI IT
0
3
RI_1
TI_1
0
Low priority
interrupt
Individual Enable
Global Disable
Each of the interrupt sources can be individually enabled or disabled by setting or clearing a bit
in the Interrupt Enable register (Table 84 and Table 82). This register also contains a global disable bit, which must be cleared to disable all interrupts at once.
Each interrupt source can also be individually programmed to one out of four priority levels by
setting or clearing a bit in the Interrupt Priority register (Table 85) and in the Interrupt Priority
High register (Table 83 and Table 84) shows the bit values and priority levels associated with
each combination.
109
7663E–8051–10/08
Registers
Table 80. Priority Level Bit Values
iph. x
ipl. x
interrupt level priority
0
0
0 (lowest)
0
1
1
1
0
2
1
1
3 (highest)
A low-priority interrupt can be interrupted by a high priority interrupt, but not by another low-priority interrupt. A high-priority interrupt can’t be interrupted by any other interrupt source.
If two interrupt requests of different priority levels are received simultaneously, the request of
higher priority level is serviced. If interrupt requests of the same priority level are received simultaneously, an internal polling sequence determines which request is serviced. Thus within each
priority level there is a second priority structure determined by the polling sequence.
110
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 81. IEN0 Register
IEN0 - Interrupt Enable Register (A8h)
7
6
5
4
3
2
1
0
EA
EC
ET2
ES
ET1
EX1
ET0
EX0
Bit
Bit
Number
Mnemonic
7
EA
6
EC
Description
Enable All interrupt bit
Cleared to disable all interrupts.
Set to enable all interrupts.
PCA interrupt enable bit
Cleared to disable.
Set to enable.
5
ET2
Timer 2 overflow interrupt Enable bit
Cleared to disable timer 2 overflow interrupt.
Set to enable timer 2 overflow interrupt.
4
ES
Serial port 0 Enable bit
Cleared to disable serial port interrupt.
Set to enable serial port interrupt.
3
ET1
Timer 1 overflow interrupt Enable bit
Cleared to disable timer 1 overflow interrupt.
Set to enable timer 1 overflow interrupt.
2
EX1
External interrupt 1 Enable bit
Cleared to disable external interrupt 1.
Set to enable external interrupt 1.
1
ET0
Timer 0 overflow interrupt Enable bit
Cleared to disable timer 0 overflow interrupt.
Set to enable timer 0 overflow interrupt.
0
EX0
External interrupt 0 Enable bit
Cleared to disable external interrupt 0.
Set to enable external interrupt 0.
Reset Value = 0000 0000b
Bit addressable
111
7663E–8051–10/08
Table 82. IPL0 Register
IPL0 - Interrupt Priority Register (B8h)
7
6
5
4
3
2
1
0
-
PPCL
PT2L
PSL
PT1L
PX1L
PT0L
PX0L
Bit
Bit
Number
Mnemonic
7
-
6
PPCL
PCA interrupt Priority bit
Refer to PPCH for priority level.
5
PT2L
Timer 2 overflow interrupt Priority bit
Refer to PT2H for priority level.
4
PSL
Serial port 0 Priority bit
Refer to PSH for priority level.
3
PT1L
Timer 1 overflow interrupt Priority bit
Refer to PT1H for priority level.
2
PX1L
External interrupt 1 Priority bit
Refer to PX1H for priority level.
1
PT0L
Timer 0 overflow interrupt Priority bit
Refer to PT0H for priority level.
0
PX0L
External interrupt 0 Priority bit
Refer to PX0H for priority level.
Description
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Reset Value = X000 0000b
Bit addressable
112
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 83. IPH0 Register
IPH0 - Interrupt Priority High Register (B7h)
7
6
5
4
3
2
1
0
-
PPCH
PT2H
PSH
PT1H
PX1H
PT0H
PX0H
Bit
Number
Mnemonic
7
-
6
5
4
3
2
1
0
Bit
Description
Reserved
The value read from this bit is indeterminate. Do not set this bit.
PPCH
PCA interrupt Priority high bit.
PPCH PPCL Priority Level
0
0
Lowest
0
1
1
0
1
1
Highest
PT2H
Timer 2 overflow interrupt Priority High bit
PT2H PT2L Priority Level
0
0
Lowest
0
1
1
0
1
1
Highest
PSH
Serial port Priority High bit
PSH PSL
Priority Level
0
0
Lowest
0
1
1
0
1
1
Highest
PT1H
Timer 1 overflow interrupt Priority High bit
PT1H PT1L Priority Level
0
0
Lowest
0
1
1
0
1
1
Highest
PX1H
External interrupt 1 Priority High bit
PX1H PX1L Priority Level
0
0
Lowest
0
1
1
0
1
1
Highest
PT0H
Timer 0 overflow interrupt Priority High bit
PT0H PT0L Priority Level
0
0
Lowest
0
1
1
0
1
1
Highest
PX0H
External interrupt 0 Priority High bit
PX0H PX0L Priority Level
0
0
Lowest
0
1
1
0
1
1
Highest
Reset Value = X000 0000b
Not bit addressable
113
7663E–8051–10/08
Table 84. IEN1 Register
IEN1 - Interrupt Enable Register (B1h)
7
6
5
4
3
2
1
0
-
-
-
-
ES_1
ESPI
ETWI
EKBD
Bit
Bit
Number
Mnemonic
7
-
Reserved
6
-
Reserved
5
-
Reserved
4
-
Reserved
3
ES_1
2
ESPI
Description
Serial port 1 Enable bit
Cleared to disable serial port interrupt.
Set to enable serial port interrupt.
SPI interrupt Enable bit
Cleared to disable SPI interrupt.
Set to enable SPI interrupt.
TWI interrupt Enable bit
1
ETWI
Cleared to disable TWI interrupt.
Set to enable TWI interrupt.
0
EKBD
Keyboard interrupt Enable bit
Cleared to disable keyboard interrupt.
Set to enable keyboard interrupt.
Reset Value = XXXX 00x0b
Bit addressable
114
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 85. IPL1 Register
IPL1 - Interrupt Priority Register (B2h)
7
6
5
4
3
2
1
0
-
-
-
-
PSL_1
SPIL
TWIL
KBDL
Bit
Bit
Number
Mnemonic
7
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
6
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
5
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
4
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
3
PSL_1
2
SPIL
1
TWIL
0
KBDL
Description
Serial port 1 Priority bit
Refer to PSH_1 for priority level.
SPI interrupt Priority bit
Refer to SPIH for priority level.
TWI interrupt Priority bit
Refer to TWIH for priority level.
Keyboard interrupt Priority bit
Refer to KBDH for priority level.
Reset Value = XXXX 00X0b
Bit addressable
115
7663E–8051–10/08
Table 86. IPH1 Register
IPH1 - Interrupt Priority High Register (B3h)
7
6
5
4
3
2
1
0
-
-
-
-
PSH_1
SPIH
TWIH
KBDH
Bit
Number
Mnemonic
7
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
6
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
5
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
4
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
3
2
1
0
Bit
Description
PSH_1
Serial port 1 Priority High bit
PSH_1 PSL_1 Priority Level
0
0
Lowest
0
1
1
0
1
1
Highest
SPIH
SPI interrupt Priority High bit
SPIH SPIL Priority Level
0
0
Lowest
0
1
1
0
1
1
Highest
TWIH
TWI interrupt Priority High bit
TWIH TWIL Priority Level
0
0
Lowest
0
1
1
0
1
1
Highest
KBDH
Keyboard interrupt Priority High bit
KB DH
KBDL Priority Level
0
0
Lowest
0
1
1
0
1
1
Highest
Reset Value = XXXX 00X0b
Not bit addressable
116
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Interrupt Sources
and Vector
Addresses
Table 87. Interrupt Sources and Vector Addresses
Interrupt
Request
Vector
Number
Polling Priority
Interrupt Source
Address
0
0
Reset
1
1
INT0
IE0
0003h
2
2
Timer 0
TF0
000Bh
3
3
INT1
IE1
0013h
4
4
Timer 1
IF1
001Bh
5
6
UART0
RI+TI
0023h
6
7
Timer 2
TF2+EXF2
002Bh
7
5
PCA
CF + CCFn (n = 0-4)
0033h
8
8
Keyboard
KBDIT
003Bh
9
9
TWI
TWIIT
0043h
10
10
SPI
SPIIT
004Bh
11
11
UART1
RI_1+TI_1
0053h
0000h
117
7663E–8051–10/08
Power Management
Introduction
Two power reduction modes are implemented in the AT89C51RE2. The Idle mode and the
Power-Down mode. These modes are detailed in the following sections. In addition to these
power reduction modes, the clocks of the core and peripherals can be dynamically divided by 2
using the X2 mode detailed in Section “Enhanced Features”, page 13.
Idle Mode
Idle mode is a power reduction mode that reduces the power consumption. In this mode, program execution halts. Idle mode freezes the clock to the CPU at known states while the
peripherals continue to be clocked. The CPU status before entering Idle mode is preserved, i.e.,
the program counter and program status word register retain their data for the duration of Idle
mode. The contents of the SFRs and RAM are also retained. The status of the Port pins during
Idle mode is detailed in Table 88.
Entering Idle Mode
To enter Idle mode, set the IDL bit in PCON register (see Table 89). The AT89C51RE2 enters
Idle mode upon execution of the instruction that sets IDL bit. The instruction that sets IDL bit is
the last instruction executed.
Note:
Exiting Idle Mode
If IDL bit and PD bit are set simultaneously, the AT89C51RE2 enters Power-Down mode. Then it
does not go in Idle mode when exiting Power-Down mode.
There are two ways to exit Idle mode:
1. Generate an enabled interrupt.
–
Hardware clears IDL bit in PCON register which restores the clock to the CPU.
Execution resumes with the interrupt service routine. Upon completion of the
interrupt service routine, program execution resumes with the instruction
immediately following the instruction that activated Idle mode. The general purpose
flags (GF1 and GF0 in PCON register) may be used to indicate whether an interrupt
occurred during normal operation or during Idle mode. When Idle mode is exited by
an interrupt, the interrupt service routine may examine GF1 and GF0.
2. Generate a reset.
–
Note:
A logic high on the RST pin clears IDL bit in PCON register directly and
asynchronously. This restores the clock to the CPU. Program execution momentarily
resumes with the instruction immediately following the instruction that activated the
Idle mode and may continue for a number of clock cycles before the internal reset
algorithm takes control. Reset initializes the AT89C51RE2 and vectors the CPU to
address C:0000h.
During the time that execution resumes, the internal RAM cannot be accessed; however, it is possible for the Port pins to be accessed. To avoid unexpected outputs at the Port pins, the instruction
immediately following the instruction that activated Idle mode should not write to a Port pin or to
the external RAM.
Power-Down Mode The Power-Down mode places the AT89C51RE2 in a very low power state. Power-Down mode
stops the oscillator, freezes all clock at known states. The CPU status prior to entering PowerDown mode is preserved, i.e., the program counter, program status word register retain their
data for the duration of Power-Down mode. In addition, the SFR and RAM contents are preserved. The status of the Port pins during Power-Down mode is detailed in Table 88.
Note:
118
VCC may be reduced to as low as VRET during Power-Down mode to further reduce power dissipation. Take care, however, that VDD is not reduced until Power-Down mode is invoked.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Entering Power-Down
Mode
Exiting Power-Down
Mode
To enter Power-Down mode, set PD bit in PCON register. The AT89C51RE2 enters the PowerDown mode upon execution of the instruction that sets PD bit. The instruction that sets PD bit is
the last instruction executed.
Note:
If VCC was reduced during the Power-Down mode, do not exit Power-Down mode until VCC is
restored to the normal operating level.
There are two ways to exit the Power-Down mode:
1. Generate an enabled external interrupt.
–
The AT89C51RE2 provides capability to exit from Power-Down using INT0#, INT1#.
Hardware clears PD bit in PCON register which starts the oscillator and restores the
clocks to the CPU and peripherals. Using INTx# input, execution resumes when the
input is released (see Figure 45). Execution resumes with the interrupt service
routine. Upon completion of the interrupt service routine, program execution
resumes with the instruction immediately following the instruction that activated
Power-Down mode.
Note:
The external interrupt used to exit Power-Down mode must be configured as level sensitive
(INT0# and INT1#) and must be assigned the highest priority. In addition, the duration of the interrupt must be long enough to allow the oscillator to stabilize. The execution will only resume when
the interrupt is deasserted.
Note:
Exit from power-down by external interrupt does not affect the SFRs nor the internal RAM content.
Figure 45. Power-Down Exit Waveform Using INT1:0#
INT1:0#
OSC
Active phase
Power-down phase
Oscillator restart phase
Active phase
2. Generate a reset.
–
A logic high on the RST pin clears PD bit in PCON register directly and
asynchronously. This starts the oscillator and restores the clock to the CPU and
peripherals. Program execution momentarily resumes with the instruction
immediately following the instruction that activated Power-Down mode and may
continue for a number of clock cycles before the internal reset algorithm takes
control. Reset initializes the AT89C51RE2 and vectors the CPU to address 0000h.
Note:
During the time that execution resumes, the internal RAM cannot be accessed; however, it is possible for the Port pins to be accessed. To avoid unexpected outputs at the Port pins, the instruction
immediately following the instruction that activated the Power-Down mode should not write to a
Port pin or to the external RAM.
Note:
Exit from power-down by reset redefines all the SFRs, but does not affect the internal RAM
content.
119
7663E–8051–10/08
Table 88. Pin Conditions in Special Operating Modes
120
Mode
Port 0
Port 1
Port 2
Port 3
Port 4
ALE
PSEN#
Reset
Floating
High
High
High
High
High
High
Idle (internal
code)
Data
Data
Data
Data
Data
High
High
Idle (external
code)
Floating
Data
Data
Data
Data
High
High
Power-Down
(internal
code)
Data
Data
Data
Data
Data
Low
Low
Power-Down
(external
code)
Floating
Data
Data
Data
Data
Low
Low
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Registers
Table 89. PCON Register
PCON (87:h) Power configuration Register
7
6
5
4
3
2
1
0
SMOD1
SMOD0
-
POF
GF1
GF0
PD
IDL
Bit Number
Bit
Mnemonic
Description
7
SMOD1
Serial Port Mode bit 1
Set to select double baud rate in mode 1, 2 or 3.
6
SMOD0
Serial Port Mode bit 0
Cleared to select SM0 bit in SCON register.
Set to select FE bit in SCON register.
5
-
4
POF
Power-Off Flag
Cleared to recognize next reset type.
Set by hardware when VCC rises from 0 to its nominal voltage. Can also be set by
software.
3
GF1
General Purpose flag 1
One use is to indicate whether an interrupt occurred during normal operation or during
Idle mode.
2
GF0
General Purpose flag 0
One use is to indicate whether an interrupt occurred during normal operation or during
Idle mode.
1
PD
Power-Down Mode bit
Cleared by hardware when an interrupt or reset occurs.
Set to activate the Power-Down mode.
If IDL and PD are both set, PD takes precedence.
0
IDL
Idle Mode bit
Cleared by hardware when an interrupt or reset occurs.
Set to activate the Idle mode.
If IDL and PD are both set, PD takes precedence.
reserved
Reset Value= XXXX 0000b
121
7663E–8051–10/08
Oscillator
To optimize the power consumption and execution time needed for a specific task, an internal
prescaler feature has been implemented between the oscillator and the CPU and peripherals.
Registers
Table 90. CKRL Register
CKRL – Clock Reload Register (97h)
7
6
5
4
3
2
1
0
CKRL7
CKRL6
CKRL5
CKRL4
CKRL3
CKRL2
CKRL1
CKRL0
Bit Number
Mnemonic
7:0
CKRL
Description
Clock Reload Register
Prescaler value
Reset Value = 1111 1111b
Not bit addressable
Table 91. PCON Register
PCON – Power Control Register (87h)
7
6
5
4
3
2
1
0
SMOD1
SMOD0
-
POF
GF1
GF0
PD
IDL
Bit Number
Bit Mnemonic
Description
7
SMOD1
Serial Port Mode bit 1
Set to select double baud rate in mode 1, 2 or 3.
6
SMOD0
Serial Port Mode bit 0
Cleared to select SM0 bit in SCON register.
Set to select FE bit in SCON register.
5
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
4
POF
Power-off Flag
Cleared by software to recognize the next reset type.
Set by hardware when VCC rises from 0 to its nominal voltage. Can also be
set by software.
3
GF1
General-purpose Flag
Cleared by software for general-purpose usage.
Set by software for general-purpose usage.
2
GF0
General-purpose Flag
Cleared by software for general-purpose usage.
Set by software for general-purpose usage.
1
PD
Power-down Mode bit
Cleared by hardware when reset occurs.
Set to enter power-down mode.
0
IDL
Idle Mode bit
Cleared by hardware when interrupt or reset occurs.
Set to enter idle mode.
Reset Value = 00X1 0000b Not bit addressable
122
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Functional Block Diagram
Figure 46. Functional Oscillator Block Diagram
Reload
Reset
CKRL
FOSC
Xtal1
Osc
1
Xtal2
:2
8-bit
Prescaler-Divider
0
1
CLK
Periph
X2
0
CKCON0
CLK
CPU
Peripheral Clock
CPU Clock
Idle
CKRL = 0xFF?
Prescaler Divider
•
A hardware RESET puts the prescaler divider in the following state:
•
•
CKRL = FFh: FCLK CPU = FCLK PERIPH = FOSC/2 (Standard C51 feature)
Any value between FFh down to 00h can be written by software into CKRL register in order
to divide frequency of the selected oscillator:
•
CKRL = 00h: minimum frequency
FCLK CPU = FCLK PERIPH = FOSC/1020 (Standard Mode)
FCLK CPU = FCLK PERIPH = FOSC/510 (X2 Mode)
•
CKRL = FFh: maximum frequency
FCLK CPU = FCLK PERIPH = FOSC/2 (Standard Mode)
FCLK CPU = FCLK PERIPH = FOSC (X2 Mode)
FCLK CPU and FCLK PERIPH
In X2 Mode, for CKRL<>0xFF:
F OSC
F CPU = F CLKPERIPH = ----------------------------------------------
2 × ( 255 – CKRL )
In X1 Mode, for CKRL<>0xFF then:
F OSC
F CPU = F CLKPERIPH = ----------------------------------------------
4 × ( 255 – CKRL )
123
7663E–8051–10/08
Hardware
Watchdog
Timer
The WDT is intended as a recovery method in situations where the CPU may be subjected to
software upset. The WDT consists of a 14-bit counter and the WatchDog Timer ReSeT
(WDTRST) SFR. The WDT is by default disabled from exiting reset. To enable the WDT, user
must write 01EH and 0E1H in sequence to the WDTRST, SFR location 0A6H. When WDT is
enabled, it will increment every machine cycle while the oscillator is running and there is no way
to disable the WDT except through reset (either hardware reset or WDT overflow reset). When
WDT overflows, it will drive an output RESET HIGH pulse at the RST-pin.
Using the WDT
To enable the WDT, user must write 01EH and 0E1H in sequence to the WDTRST, SFR location 0A6H. When WDT is enabled, the user needs to service it by writing to 01EH and 0E1H to
WDTRST to avoid WDT overflow. The 14-bit counter overflows when it reaches 16383 (3FFFH)
and this will reset the device. When WDT is enabled, it will increment every machine cycle while
the oscillator is running. This means the user must reset the WDT at least every 16383 machine
cycle. To reset the WDT the user must write 01EH and 0E1H to WDTRST. WDTRST is a write
only register. The WDT counter cannot be read or written. When WDT overflows, it will generate
an output RESET pulse at the RST-pin. The RESET pulse duration is 96 x TCLK PERIPH, where
TCLK PERIPH= 1/FCLK PERIPH. To make the best use of the WDT, it should be serviced in those sections of code that will periodically be executed within the time required to prevent a WDT reset.
To have a more powerful WDT, a 27 counter has been added to extend the Time-out capability,
ranking from 16ms to 2s @ FOSCA = 12MHz. To manage this feature, refer to WDTPRG register
description, Table 92.
Table 92. WDTRST Register
WDTRST - Watchdog Reset Register (0A6h)
7
6
5
4
3
2
1
0
-
-
-
-
-
-
-
-
Reset Value = XXXX XXXXb
Write only, this SFR is used to reset/enable the WDT by writing 01EH then 0E1H in sequence.
124
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 93. WDTPRG Register
WDTPRG - Watchdog Timer Out Register (0A7h)
7
6
5
4
3
2
1
0
-
-
-
-
-
S2
S1
S0
Bit
Bit
Number
Mnemonic
7
-
6
-
5
-
4
-
3
-
2
S2
WDT Time-out select bit 2
1
S1
WDT Time-out select bit 1
0
S0
WDT Time-out select bit 0
Description
Reserved
The value read from this bit is undetermined. Do not try to set this bit.
S2
0
0
0
0
1
1
1
1
S1
0
0
1
1
0
0
1
1
S0
0
1
0
1
0
1
0
1
Selected Time-out
(214 - 1) machine cycles, 16. 3 ms @ FOSCA =12 MHz
(215 - 1) machine cycles, 32.7 ms @ FOSCA=12 MHz
(216 - 1) machine cycles, 65. 5 ms @ FOSCA=12 MHz
(217 - 1) machine cycles, 131 ms @ FOSCA=12 MHz
(218 - 1) machine cycles, 262 ms @ FOSCA=12 MHz
(219 - 1) machine cycles, 542 ms @ FOSCA=12 MHz
(220 - 1) machine cycles, 1.05 s @ FOSCA=12 MHz
(221 - 1) machine cycles, 2.09 s @ FOSCA=12 MHz
Reset value = XXXX X000
WDT During Power In Power Down mode the oscillator stops, which means the WDT also stops. While in Power
Down mode the user does not need to service the WDT. There are 2 methods of exiting Power
Down and Idle
Down mode: by a hardware reset or via a level activated external interrupt which is enabled prior
to entering Power Down mode. When Power Down is exited with hardware reset, servicing the
WDT should occur as it normally should whenever the AT89C51RE2 is reset. Exiting Power
Down with an interrupt is significantly different. The interrupt is held low long enough for the
oscillator to stabilize. When the interrupt is brought high, the interrupt is serviced. To prevent the
WDT from resetting the device while the interrupt pin is held low, the WDT is not started until the
interrupt is pulled high. It is suggested that the WDT be reset during the interrupt service routine.
To ensure that the WDT does not overflow within a few states of exiting of powerdown, it is better to reset the WDT just before entering powerdown.
In the Idle mode, the oscillator continues to run. To prevent the WDT from resetting the
AT89C51RE2 while in Idle mode, the user should always set up a timer that will periodically exit
Idle, service the WDT, and re-enter Idle mode.
125
7663E–8051–10/08
Reduced EMI
Mode
The ALE signal is used to demultiplex address and data buses on port 0 when used with external program or data memory. Nevertheless, during internal code execution, ALE signal is still
generated. In order to reduce EMI, ALE signal can be disabled by setting AO bit.
The AO bit is located in AUXR register at bit location 0. As soon as AO is set, ALE is no longer
output but remains active during MOVX and MOVC instructions and external fetches. During
ALE disabling, ALE pin is weakly pulled high.
Table 94. AUXR Register
AUXR - Auxiliary Register (8Eh)
7
6
5
4
3
2
1
0
-
-
M0
XRS2
XRS1
XRS0
EXTRAM
AO
Bit
Bit
Number
Mnemonic
7
-
6
-
Description
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Pulse length
5
M0
Cleared to stretch MOVX control: the RD/ and the WR/ pulse length is 6 clock periods
(default).
Set to stretch MOVX control: the RD/ and the WR/ pulse length is 30 clock periods.
4
XRS2
XRAM Size
3
XRS1
XRS2
0
XRS1
0
0
0
1
512 bytes
0
1
0
768 bytes(default)
0
1
1
1024 bytes
1
0
0
1792 bytes
2
XRS0
XRS0 XRAM size
0
256 bytes
EXTRAM bit
Cleared to access internal XRAM using movx @ Ri/ @ DPTR.
1
EXTRAM
Set to access external memory.
Programmed by hardware after Power-up regarding Hardware Security Byte (HSB),
default setting, XRAM selected.
0
AO
ALE Output bit
Cleared, ALE is emitted at a constant rate of 1/6 the oscillator frequency (or 1/3 if X2
mode is used). (default) Set, ALE is active only during a MOVX or MOVC instruction is
used.
Reset Value = XX00 10’HSB. XRAM’0b
Not bit addressable
126
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Keyboard
Interface
The AT89C51RE2 implements a keyboard interface allowing the connection of a
8 x n matrix keyboard. It is based on 8 inputs with programmable interrupt capability on both
high or low level. These inputs are available as alternate function of P1 and allow to exit from
idle and power down modes.
The keyboard interface interfaces with the C51 core through 3 special function registers: KBLS,
the Keyboard Level Selection register (Table 97), KBE, The Keyboard interrupt Enable register
(Table 96), and KBF, the Keyboard Flag register (Table 95).
Interrupt
The keyboard inputs are considered as 8 independent interrupt sources sharing the same interrupt vector. An interrupt enable bit (KBD in IE1) allows global enable or disable of the keyboard
interrupt (see Figure 47). As detailed in Figure 48 each keyboard input has the capability to
detect a programmable level according to KBLS. x bit value. Level detection is then reported in
interrupt flags KBF. x that can be masked by software using KBE. x bits.
This structure allow keyboard arrangement from 1 by n to 8 by n matrix and allow usage of P1
inputs for other purpose.
Figure 47. Keyboard Interface Block Diagram
Vcc
0
P1:x
KBF. x
1
Internal Pullup
KBE. x
KBLS. x
Figure 48. Keyboard Input Circuitry
P1.0
Input Circuitry
P1.1
Input Circuitry
P1.2
Input Circuitry
P1.3
Input Circuitry
P1.4
Input Circuitry
P1.5
Input Circuitry
P1.6
Input Circuitry
P1.7
Input Circuitry
KBDIT
Power Reduction
Mode
KBD
IE1
Keyboard Interface
Interrupt Request
P1 inputs allow exit from idle and power down modes as detailed in Section “Power Management”, page 118.
127
7663E–8051–10/08
Registers
Table 95. KBF Register
KBF-Keyboard Flag Register (9Eh)
7
6
5
4
3
2
1
0
KBF7
KBF6
KBF5
KBF4
KBF3
KBF2
KBF1
KBF0
Bit Number
Bit
Mnemonic
Description
7
6
5
4
3
2
1
0
KBF7
Keyboard line 7 flag
Set by hardware when the Port line 7 detects a programmed level. It generates a
Keyboard interrupt request if the KBKBIE. 7 bit in KBIE register is set.
Must be cleared by software.
KBF6
Keyboard line 6 flag
Set by hardware when the Port line 6 detects a programmed level. It generates a
Keyboard interrupt request if the KBIE. 6 bit in KBIE register is set.
Must be cleared by software.
KBF5
Keyboard line 5 flag
Set by hardware when the Port line 5 detects a programmed level. It generates a
Keyboard interrupt request if the KBIE. 5 bit in KBIE register is set.
Must be cleared by software.
KBF4
Keyboard line 4 flag
Set by hardware when the Port line 4 detects a programmed level. It generates a
Keyboard interrupt request if the KBIE. 4 bit in KBIE register is set.
Must be cleared by software.
KBF3
Keyboard line 3 flag
Set by hardware when the Port line 3 detects a programmed level. It generates a
Keyboard interrupt request if the KBIE. 3 bit in KBIE register is set.
Must be cleared by software.
KBF2
Keyboard line 2 flag
Set by hardware when the Port line 2 detects a programmed level. It generates a
Keyboard interrupt request if the KBIE. 2 bit in KBIE register is set.
Must be cleared by software.
KBF1
Keyboard line 1 flag
Set by hardware when the Port line 1 detects a programmed level. It generates a
Keyboard interrupt request if the KBIE. 1 bit in KBIE register is set.
Must be cleared by software.
KBF0
Keyboard line 0 flag
Set by hardware when the Port line 0 detects a programmed level. It generates a
Keyboard interrupt request if the KBIE. 0 bit in KBIE register is set.
Must be cleared by software.
Reset Value= 0000 0000b
128
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 96. KBE Register
KBE-Keyboard Input Enable Register (9Dh)
7
6
5
4
3
2
1
0
KBE7
KBE6
KBE5
KBE4
KBE3
KBE2
KBE1
KBE0
Bit
Number
Bit
Mnemonic
Description
7
KBE7
Keyboard line 7 Enable bit
Cleared to enable standard I/O pin.
Set to enable KBF. 7 bit in KBF register to generate an interrupt request.
6
KBE6
Keyboard line 6 Enable bit
Cleared to enable standard I/O pin.
Set to enable KBF. 6 bit in KBF register to generate an interrupt request.
5
KBE5
Keyboard line 5 Enable bit
Cleared to enable standard I/O pin.
Set to enable KBF. 5 bit in KBF register to generate an interrupt request.
4
KBE4
Keyboard line 4 Enable bit
Cleared to enable standard I/O pin.
Set to enable KBF. 4 bit in KBF register to generate an interrupt request.
3
KBE3
Keyboard line 3 Enable bit
Cleared to enable standard I/O pin.
Set to enable KBF. 3 bit in KBF register to generate an interrupt request.
2
KBE2
Keyboard line 2 Enable bit
Cleared to enable standard I/O pin.
Set to enable KBF. 2 bit in KBF register to generate an interrupt request.
1
KBE1
Keyboard line 1 Enable bit
Cleared to enable standard I/O pin.
Set to enable KBF. 1 bit in KBF register to generate an interrupt request.
0
KBE0
Keyboard line 0 Enable bit
Cleared to enable standard I/O pin.
Set to enable KBF. 0 bit in KBF register to generate an interrupt request.
Reset Value= 0000 0000b
129
7663E–8051–10/08
Table 97. KBLS Register
KBLS-Keyboard Level Selector Register (9Ch)
7
6
5
4
3
2
1
0
KBLS7
KBLS6
KBLS5
KBLS4
KBLS3
KBLS2
KBLS1
KBLS0
Bit Number
Bit
Mnemonic
Description
7
KBLS7
Keyboard line 7 Level Selection bit
Cleared to enable a low level detection on Port line 7.
Set to enable a high level detection on Port line 7.
6
KBLS6
Keyboard line 6 Level Selection bit
Cleared to enable a low level detection on Port line 6.
Set to enable a high level detection on Port line 6.
5
KBLS5
Keyboard line 5 Level Selection bit
Cleared to enable a low level detection on Port line 5.
Set to enable a high level detection on Port line 5.
4
KBLS4
Keyboard line 4 Level Selection bit
Cleared to enable a low level detection on Port line 4.
Set to enable a high level detection on Port line 4.
3
KBLS3
Keyboard line 3 Level Selection bit
Cleared to enable a low level detection on Port line 3.
Set to enable a high level detection on Port line 3.
2
KBLS2
Keyboard line 2 Level Selection bit
Cleared to enable a low level detection on Port line 2.
Set to enable a high level detection on Port line 2.
1
KBLS1
Keyboard line 1 Level Selection bit
Cleared to enable a low level detection on Port line 1.
Set to enable a high level detection on Port line 1.
0
KBLS0
Keyboard line 0 Level Selection bit
Cleared to enable a low level detection on Port line 0.
Set to enable a high level detection on Port line 0.
Reset Value= 0000 0000b
130
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
2-wire Interface (TWI)
This section describes the 2-wire interface. The 2-wire bus 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 serial data
transfer is limited to 400 Kbit/s in standard mode. Various communication configuration
can be designed using this bus. Figure 49 shows a typical 2-wire bus configuration. All
the devices connected to the bus can be master and slave.
Figure 49. 2-wire Bus Configuration
device1
device2
device3
...
deviceN
SCL
SDA
131
7663D–8051–10/08
Figure 50. Block Diagram
8
Address Register
SSADR
Comparator
Input
Filter
SDA
PI2.1
Output
Stage
SSDAT
ACK
Shift Register
Arbitration &
Sink Logic
Input
Filter
Timing &
Control
logic
SCL
PI2.0
Output
Stage
FCLK PERIPH/4
Internal Bus
8
Interrupt
Serial clock
generator
Timer 1
overflow
SSCON
Control Register
7
Status
Bits
SSCS
Status
Decoder
Status Register
8
132
AT89C51RE2
7663D–8051–10/08
AT89C51RE2
Description
The CPU interfaces to the 2-wire logic via the following four 8-bit special function registers: the Synchronous Serial Control register (SSCON; Table 107), the Synchronous
Serial Data register (SSDAT; Table 108), the Synchronous Serial Control and Status
register (SSCS; Table 109) and the Synchronous Serial Address register (SSADR Table
112).
SSCON is used to enable the TWI interface, to program the bit rate (see Table 100), to
enable slave modes, to acknowledge or not a received data, to send a START or a
STOP condition on the 2-wire bus, and to acknowledge a serial interrupt. A hardware
reset disables the TWI module.
SSCS contains a status code which reflects the status of the 2-wire logic and the 2-wire
bus. The three least significant bits are always zero. The five most significant bits contains the status code. There are 26 possible status codes. When SSCS contains F8h,
no relevant state information is available and no serial interrupt is requested. A valid status code is available in SSCS one machine cycle after SI is set by hardware and is still
present one machine cycle after SI has been reset by software. to Table 106. give the
status for the master modes and miscellaneous states.
SSDAT contains a byte of serial data to be transmitted or a byte which has just been
received. It is addressable while it is not in process of shifting a byte. This occurs when
2-wire logic is in a defined state and the serial interrupt flag is set. Data in SSDAT
remains stable as long as SI is set. While data is being shifted out, data on the bus is
simultaneously shifted in; SSDAT always contains the last byte present on the bus.
SSADR may be loaded with the 7-bit slave address (7 most significant bits) to which the
TWI module will respond when programmed as a slave transmitter or receiver. The LSB
is used to enable general call address (00h) recognition.
Figure 51 shows how a data transfer is accomplished on the 2-wire bus.
Figure 51. Complete Data Transfer on 2-wire Bus
SDA
MSB
acknowledgement
signal from receiver
acknowledgement
signal from receiver
SCL
1
2
7
S
start
condition
8
9
ACK
1
2
3-8
9
ACK
clock line held low
while interrupts are serviced
P
stop
condition
The four operating modes are:
•
Master Transmitter
•
Master Receiver
•
Slave transmitter
•
Slave receiver
Data transfer in each mode of operation is shown in Table to Table 106 and Figure 52.
to Figure 55.. These figures contain the following abbreviations:
S : START condition
R : Read bit (high level at SDA)
133
7663D–8051–10/08
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
In Figure 52 to Figure 55, circles are used to indicate when the serial interrupt flag is set.
The numbers in the circles show the status code held in SSCS. At these points, a service routine must be executed to continue or complete the serial transfer. These service
routines are not critical since the serial transfer is suspended until the serial interrupt
flag is cleared by software.
When the serial interrupt routine is entered, the status code in SSCS is used to branch
to the appropriate service routine. For each status code, the required software action
and details of the following serial transfer are given in Table to Table 106.
Master Transmitter Mode
In the master transmitter mode, a number of data bytes are transmitted to a slave
receiver (Figure 52). Before the master transmitter mode can be entered, SSCON must
be initialised as follows:
Table 98. SSCON Initialization
CR2
SSIE
STA
STO
SI
AA
CR1
CR0
bit rate
1
0
0
0
X
bit rate
bit rate
CR0, CR1 and CR2 define the internal serial bit rate if external bit rate generator is not
used. SSIE must be set to enable TWI. STA, STO and SI must be cleared.
The master transmitter mode may now be entered by setting the STA bit. The 2-wire
logic will now test the 2-wire bus and generate a START condition as soon as the bus
becomes free. When a START condition is transmitted, the serial interrupt flag (SI bit in
SSCON) is set, and the status code in SSCS will be 08h. This status must be used to
vector to an interrupt routine that loads SSDAT with the slave address and the data
direction bit (SLA+W).
When the slave address and the direction bit have been transmitted and an acknowledgement bit has been received, SI is set again and a number of status code in SSCS
are possible. There are 18h, 20h or 38h for the master mode and also 68h, 78h or B0h if
the slave mode was enabled (AA=logic 1). The appropriate action to be taken for each
of these status code is detailed in Table . This scheme is repeated until a STOP condition is transmitted.
SSIE, CR2, CR1 and CR0 are not affected by the serial transfer and are referred to
Table 7 to Table 11. After a repeated START condition (state 10h) the TWI module may
switch to the master receiver mode by loading SSDAT with SLA+R.
Master Receiver Mode
134
In the master receiver mode, a number of data bytes are received from a slave transmitter (Figure 53). The transfer is initialized as in the master transmitter mode. When the
START condition has been transmitted, the interrupt routine must load SSDAT with the
7-bit slave address and the data direction bit (SLA+R). The serial interrupt flag SI must
then be cleared before the serial transfer can continue.
AT89C51RE2
7663D–8051–10/08
AT89C51RE2
When the slave address and the direction bit have been transmitted and an acknowledgement bit has been received, the serial interrupt flag is set again and a number of
status code in SSCS are possible. There are 40h, 48h or 38h for the master mode and
also 68h, 78h or B0h if the slave mode was enabled (AA=logic 1). The appropriate
action to be taken for each of these status code is detailed in Table . This scheme is
repeated until a STOP condition is transmitted.
SSIE, CR2, CR1 and CR0 are not affected by the serial transfer and are referred to
Table 7 to Table 11. After a repeated START condition (state 10h) the TWI module may
switch to the master transmitter mode by loading SSDAT with SLA+W.
Slave Receiver Mode
In the slave receiver mode, a number of data bytes are received from a master transmitter (Figure 54). To initiate the slave receiver mode, SSADR and SSCON must be loaded
as follows:
Table 99. SSADR: Slave Receiver Mode Initialization
A6
A5
A4
A3
A2
A1
A0
GC
own slave address
The upper 7 bits are the address to which the TWI module will respond when addressed
by a master. If the LSB (GC) is set the TWI module will respond to the general call
address (00h); otherwise it ignores the general call address.
Table 100. SSCON: Slave Receiver Mode Initialization
CR2
SSIE
STA
STO
SI
AA
CR1
CR0
bit rate
1
0
0
0
1
bit rate
bit rate
CR0, CR1 and CR2 have no effect in the slave mode. SSIE must be set to enable the
TWI. The AA bit must be set to enable the own slave address or the general call address
acknowledgement. STA, STO and SI must be cleared.
When SSADR and SSCON have been initialised, the TWI module waits until it is
addressed by its own slave address followed by the data direction bit which must be at
logic 0 (W) for the TWI to operate in the slave receiver mode. After its own slave
address and the W bit have been received, the serial interrupt flag is set and a valid status code can be read from SSCS. This status code is used to vector to an interrupt
service routine.The appropriate action to be taken for each of these status code is
detailed in Table . The slave receiver mode may also be entered if arbitration is lost
while TWI is in the master mode (states 68h and 78h).
If the AA bit is reset during a transfer, TWI module will return a not acknowledge (logic 1)
to SDA after the next received data byte. While AA is reset, the TWI module does not
respond to its own slave address. However, the 2-wire bus is still monitored and
address recognition may be resume at any time by setting AA. This means that the AA
bit may be used to temporarily isolate the module from the 2-wire bus.
Slave Transmitter Mode
In the slave transmitter mode, a number of data bytes are transmitted to a master
receiver (Figure 55). Data transfer is initialized as in the slave receiver mode. When
SSADR and SSCON have been initialized, the TWI module waits until it is addressed by
135
7663D–8051–10/08
its own slave address followed by the data direction bit which must be at logic 1 (R) for
TWI to operate in the slave transmitter mode. After its own slave address and the R bit
have been received, the serial interrupt flag is set and a valid status code can be read
from SSCS. This status code is used to vector to an interrupt service routine. The appropriate action to be taken for each of these status code is detailed in Table . The slave
transmitter mode may also be entered if arbitration is lost while the TWI module is in the
master mode.
If the AA bit is reset during a transfer, the TWI module will transmit the last byte of the
transfer and enter state C0h or C8h. the TWI module is switched to the not addressed
slave mode and will ignore the master receiver if it continues the transfer. Thus the master receiver receives all 1’s as serial data. While AA is reset, the TWI module does not
respond to its own slave address. However, the 2-wire bus is still monitored and
address recognition may be resume at any time by setting AA. This means that the AA
bit may be used to temporarily isolate the TWI module from the 2-wire bus.
Miscellaneous States
There are two SSCS codes that do not correspond to a define TWI hardware state
(Table 106 ). These codes are discuss hereafter.
Status F8h indicates that no relevant information is available because the serial interrupt
flag is not set yet. This occurs between other states and when the TWI module is not
involved in a serial transfer.
Status 00h indicates that a bus error has occurred during a TWI serial transfer. A bus
error is caused when a START or a STOP condition occurs at an illegal position in the
format frame. Examples of such illegal positions happen 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 be set and SI must be cleared. This causes
the TWI module 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.
Notes
the TWI module interfaces to the external 2-wire bus via two port pins: SCL (serial clock
line) and SDA (serial data line). To avoid low level asserting on these lines when the
TWI module is enabled, the output latches of SDA and SLC must be set to logic 1.
Table 101. Bit Frequency Configuration
Bit Frequency ( kHz)
136
CR2
CR1
CR0
FOSCA= 12 MHz
FOSCA = 16 MHz
FOSCA divided by
0
0
0
47
62.5
256
0
0
1
53.5
71.5
224
0
1
0
62.5
83
192
0
1
1
75
100
160
1
0
0
-
-
Unused
1
0
1
100
133.3
120
1
1
0
200
266.6
60
1
1
1
0.5 <. < 62.5
0.67 <. < 83
96 · (256 - reload valueTimer 1)
(reload value range: 0-254 in mode 2)
AT89C51RE2
7663D–8051–10/08
AT89C51RE2
Figure 52. Format and State in the Master Transmitter Mode
MT
Successfull
transmission
to a slave
receiver
S
SLA
08h
W
A
Data
A
P
28h
18h
Next transfer
started with a
repeated start
condition
S
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
From slave to master
Other master
continues
38h
Other master
continues
A
68h
From master to slave
A or A
Data
n
78h
A
B0h
To corresponding
states in slave mode
Any number of data bytes and their associated
acknowledge bits
This number (contained in SSCS) corresponds
to a defined state of the 2-wire bus
137
7663D–8051–10/08
Table 102. Status in Master Transmitter Mode
Application software response
Status
Code
SSSTA
Status of the Twowire Bus and Twowire Hardware
To SSCON
To/From SSDAT
SSSTA
SSSTO
SSI
SSAA
Next Action Taken by Two-wire Hardware
08h
A START condition has
Write SLA+W
been transmitted
X
0
0
X
Write SLA+W
X
0
0
X
10h
A repeated START
condition has been
transmitted
Write SLA+R
X
0
0
X
Write data byte
0
0
0
X
No SSDAT action
1
0
0
X
No SSDAT action
0
1
0
X
STOP condition will be transmitted and SSSTO flag
will be reset.
No SSDAT action
1
1
0
X
STOP condition followed by a START condition will
be transmitted and SSSTO flag will be reset.
Write data byte
0
0
0
X
No SSDAT action
1
0
0
X
No SSDAT action
0
1
0
X
STOP condition will be transmitted and SSSTO flag
will be reset.
No SSDAT action
1
1
0
X
STOP condition followed by a START condition will
be transmitted and SSSTO flag will be reset.
Write data byte
0
0
0
X
No SSDAT action
1
0
0
X
No SSDAT action
0
1
0
X
STOP condition will be transmitted and SSSTO flag
will be reset.
No SSDAT action
1
1
0
X
STOP condition followed by a START condition will
be transmitted and SSSTO flag will be reset.
Write data byte
0
0
0
X
No SSDAT action
1
0
0
X
No SSDAT action
0
1
0
X
STOP condition will be transmitted and SSSTO flag
will be reset.
No SSDAT action
1
1
0
X
STOP condition followed by a START condition will
be transmitted and SSSTO flag will be reset.
No SSDAT action
0
0
0
X
Two-wire bus will be released and not addressed
slave mode will be entered.
No SSDAT action
1
0
0
X
A START condition will be transmitted when the bus
becomes free.
18h
20h
28h
30h
38h
138
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
Data byte has been
transmitted; NOT ACK
has been received
Arbitration lost in
SLA+W or data bytes
SLA+W will be transmitted.
SLA+W will be transmitted.
SLA+R will be transmitted.
Logic will switch to master receiver mode
Data byte will be transmitted.
Repeated START will be transmitted.
Data byte will be transmitted.
Repeated START will be transmitted.
Data byte will be transmitted.
Repeated START will be transmitted.
Data byte will be transmitted.
Repeated START will be transmitted.
AT89C51RE2
7663D–8051–10/08
AT89C51RE2
Figure 53. Format and State in the Master Receiver Mode
MR
Successfull
transmission
to a slave
receiver
S
SLA
08h
R
A
Data
A
50h
40h
Data
A
P
58h
Next transfer
started with a
repeated start
condition
S
SLA
R
10h
Not acknowledge
received after the
slave address
A
W
P
MT
48h
Arbitration lost in slave
address or acknowledge bit
A or A
Other master
continues
38h
Arbitration lost and
addressed as slave
From slave to master
Other master
continues
38h
Other master
continues
A
68h
From master to slave
A
Data
n
78h
A
B0h
To corresponding
states in slave mode
Any number of data bytes and their associated
acknowledge bits
This number (contained in SSCS) corresponds
to a defined state of the 2-wire bus
139
7663D–8051–10/08
Table 103. Status in Master Receiver Mode
Application software response
Status
Code
SSSTA
Status of the Twowire Bus and Twowire Hardware
To SSCON
To/From SSDAT
SSSTA
SSSTO
SSI
SSAA
Next Action Taken by Two-wire Hardware
08h
A START condition has
Write SLA+R
been transmitted
X
0
0
X
Write SLA+R
X
0
0
X
10h
A repeated START
condition has been
transmitted
Write SLA+W
X
0
0
X
SLA+W will be transmitted.
Logic will switch to master transmitter mode.
Arbitration lost in
SLA+R or NOT ACK
bit
No SSDAT action
0
0
0
X
Two-wire bus will be released and not addressed
slave mode will be entered.
No SSDAT action
1
0
0
X
A START condition will be transmitted when the bus
becomes free.
SLA+R has been
transmitted; ACK has
been received
No SSDAT action
0
0
0
0
Data byte will be received and NOT ACK will be
returned.
No SSDAT action
0
0
0
1
Data byte will be received and ACK will be returned.
No SSDAT action
1
0
0
X
No SSDAT action
0
1
0
X
STOP condition will be transmitted and SSSTO flag
will be reset.
No SSDAT action
1
1
0
X
STOP condition followed by a START condition will
be transmitted and SSSTO flag will be reset.
Read data byte
0
0
0
0
Data byte will be received and NOT ACK will be
returned.
Read data byte
0
0
0
1
Data byte will be received and ACK will be returned.
Read data byte
1
0
0
X
Read data byte
0
1
0
X
STOP condition will be transmitted and SSSTO flag
will be reset.
Read data byte
1
1
0
X
STOP condition followed by a START condition will
be transmitted and SSSTO flag will be reset.
38h
40h
48h
50h
58h
140
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
SLA+R will be transmitted.
SLA+R will be transmitted.
Repeated START will be transmitted.
Repeated START will be transmitted.
AT89C51RE2
7663D–8051–10/08
AT89C51RE2
Figure 54. Format and State in the Slave Receiver Mode
Reception of the own
slave address and one or
more data bytes. All are
acknowledged.
S
SLA
W
Data
A
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
Data
A
70h
Last data byte received is
not acknowledged.
A
90h
Data
A
P or S
90h
A0h
A
P or S
98h
A
Arbitration lost as master and
addressed as slave by general call
78h
From master to slave
From slave to master
Data
n
A
Any number of data bytes and their associated
acknowledge bits
This number (contained in SSCS) corresponds
to a defined state of the 2-wire bus
141
7663D–8051–10/08
Table 104. Status in Slave Receiver Mode
Application Software Response
Status
Code
(SSCS)
60h
68h
70h
78h
80h
88h
90h
142
To/from SSDAT
Status of the 2-wire bus and
2-wire hardware
To SSCON
STA
STO
SI
AA
Next Action Taken By 2-wire Software
Own SLA+W has been
received; ACK has been
returned
No SSDAT action or
X
0
0
0
Data byte will be received and NOT ACK will be
returned
No SSDAT action
X
0
0
1
Data byte will be received and ACK will be
returned
Arbitration lost in SLA+R/W as
master; own SLA+W has been
received; ACK has been
returned
No SSDAT action or
X
0
0
0
Data byte will be received and NOT ACK will be
returned
No SSDAT action
X
0
0
1
Data byte will be received and ACK will be
returned
General call address has been
received; ACK has been
returned
No SSDAT action or
X
0
0
0
Data byte will be received and NOT ACK will be
returned
No SSDAT action
X
0
0
1
Data byte will be received and ACK will be
returned
No SSDAT action or
X
0
0
0
Data byte will be received and NOT ACK will be
returned
No SSDAT action
X
0
0
1
Data byte will be received and ACK will be
returned
No SSDAT action or
X
0
0
0
Data byte will be received and NOT ACK will be
returned
No SSDAT action
X
0
0
1
Data byte will be received and ACK will be
returned
Read data byte or
0
0
0
0
Read data byte or
0
0
0
1
Arbitration lost in SLA+R/W as
master; general call address
has been received; ACK has
been returned
Previously addressed with
own SLA+W; data has been
received; ACK has been
returned
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
Switched to the not addressed slave mode; no
recognition of own SLA or GCA
Switched to the not addressed slave mode; own
SLA will be recognised; GCA will be recognised if
GC=logic 1
Read data byte or
1
0
0
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
0
1
Switched to the not addressed slave mode; own
SLA will be recognised; GCA will be recognised if
GC=logic 1. A START condition will be
transmitted when the bus becomes free
Read data byte or
X
0
0
0
Data byte will be received and NOT ACK will be
returned
Read data byte
X
0
0
1
Data byte will be received and ACK will be
returned
AT89C51RE2
7663D–8051–10/08
AT89C51RE2
Table 104. Status in Slave Receiver Mode (Continued)
Application Software Response
Status
Code
(SSCS)
98h
To/from SSDAT
Status of the 2-wire bus and
2-wire hardware
Previously addressed with
general call; data has been
received; NOT ACK has been
returned
STA
A0h
STO
SI
AA
Read data byte or
0
0
0
0
Read data byte or
0
0
0
1
Read data byte or
Read data byte
A STOP condition or repeated
START condition has been
received while still addressed
as slave
To SSCON
1
1
0
0
0
0
1
Switched to the not addressed slave mode; own
SLA will be recognised; GCA will be recognised if
GC=logic 1. A START condition will be
transmitted when the bus becomes free
0
0
0
No SSDAT action or
0
0
0
1
No SSDAT action
1
0
0
0
0
Switched to the not addressed slave mode; own
SLA will be recognised; GCA will be recognised if
GC=logic 1
0
0
1
Switched to the not addressed slave mode; no
recognition of own SLA or GCA
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 SSDAT action or
No SSDAT action or
Next Action Taken By 2-wire Software
Switched to the not addressed slave mode; no
recognition of own SLA or GCA
Switched to the not addressed slave mode; own
SLA will be recognised; GCA will be recognised if
GC=logic 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 recognised; GCA will be recognised if
GC=logic 1. A START condition will be
transmitted when the bus becomes free
143
7663D–8051–10/08
Figure 55. Format and State in the Slave Transmitter Mode
Reception of the
S
own slave address
and one or more
data bytes
SLA
A
R
Data
A
A8h
Arbitration lost as master
and addressed as slave
B8h
Data
A
P or S
C0h
A
B0h
Last data byte transmitted.
Switched to not addressed
slave (AA=0)
A
All 1’s P or S
C8h
From master to slave
Data
From slave to master
A
Any number of data bytes and their associated
acknowledge bits
This number (contained in SSCS) corresponds
to a defined state of the 2-wire bus
n
Table 105. Status in Slave Transmitter Mode
Application Software Response
Status
Code
(SSCS)
A8h
B0h
B8h
144
To/from SSDAT
Status of the 2-wire bus and
2-wire hardware
To SSCON
STA
STO
SI
AA
Next Action Taken By 2-wire Software
Own SLA+R has been
received; ACK has been
returned
Load data byte or
X
0
0
0
Last data byte will be transmitted and NOT ACK
will be received
Load data byte
X
0
0
1
Data byte will be transmitted and ACK will be
received
Arbitration lost in SLA+R/W as
master; own SLA+R has been
received; ACK has been
returned
Load data byte or
X
0
0
0
Last data byte will be transmitted and NOT ACK
will be received
Load data byte
X
0
0
1
Data byte will be transmitted and ACK will be
received
Data byte in SSDAT has been
transmitted; NOT ACK has
been received
Load data byte or
X
0
0
0
Last data byte will be transmitted and NOT ACK
will be received
Load data byte
X
0
0
1
Data byte will be transmitted and ACK will be
received
AT89C51RE2
7663D–8051–10/08
AT89C51RE2
Table 105. Status in Slave Transmitter Mode (Continued)
Application Software Response
Status
Code
(SSCS)
C0h
To/from SSDAT
Status of the 2-wire bus and
2-wire hardware
Data byte in SSDAT has been
transmitted; NOT ACK has
been received
To SSCON
STA
Last data byte in SSDAT has
been transmitted (AA=0); ACK
has been received
SI
AA
No SSDAT action or
0
0
0
0
No SSDAT action or
0
0
0
1
No SSDAT action or
No SSDAT action
C8h
STO
1
1
0
0
0
0
1
Switched to the not addressed slave mode; own
SLA will be recognised; GCA will be recognised if
GC=logic 1. A START condition will be transmitted
when the bus becomes free
0
0
0
No SSDAT action or
0
0
0
1
No SSDAT action
1
0
0
0
0
Switched to the not addressed slave mode; own
SLA will be recognised; GCA will be recognised if
GC=logic 1
0
0
1
Switched to the not addressed slave mode; no
recognition of own SLA or GCA
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 SSDAT action or
No SSDAT action or
Next Action Taken By 2-wire Software
Switched to the not addressed slave mode; no
recognition of own SLA or GCA
Switched to the not addressed slave mode; own
SLA will be recognised; GCA will be recognised if
GC=logic 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 recognised; GCA will be recognised if
GC=logic 1. A START condition will be transmitted
when the bus becomes free
Table 106. Miscellaneous Status
Application Software Response
To/from
SSDAT
Status
Code
(SSCS)
Status of the 2-wire
bus and 2-wire
hardware
F8h
No relevant state
information
available; SI= 0
No SSDAT
action
00h
Bus error due to an
illegal START or
STOP condition
No SSDAT
action
To SSCON
STA
STO
SI
Next Action Taken By 2-wire
AA Software
No SSCON action
Wait or proceed current transfer
0
Only the internal hardware is
affected, no STOP condition is
sent on the bus. In all cases,
the bus is released and STO is
reset.
1
0
X
145
7663D–8051–10/08
Registers
Table 107. SSCON Register
SSCON - Synchronous Serial Control register (93h)
7
6
5
4
3
2
1
0
CR2
SSIE
STA
STO
SI
AA
CR1
CR0
Bit
Number
Bit
Mnemonic Description
7
CR2
Control Rate bit 2
See Table 101.
6
SSIE
Synchronous Serial Interface Enable bit
Clear to disable the TWI module.
Set to enable the TWI module.
5
STA
Start flag
Set to send a START condition on the bus.
4
ST0
Stop flag
Set to send a STOP condition on the bus.
3
SI
Synchronous Serial Interrupt flag
Set by hardware when a serial interrupt is requested.
Must be cleared by software to acknowledge interrupt.
2
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 recognise 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.
1
CR1
Control Rate bit 1
See Table 101.
0
CR0
Control Rate bit 0
See Table 101.
Table 108. SSDAT (95h) - Syncrhonous Serial Data register (read/write)
SD7
SD6
SD5
SD4
SD3
SD2
SD1
SD0
7
6
5
4
3
2
1
0
Bit
Number
146
Bit
Mnemonic Description
7
SD7
Address bit 7 or Data bit 7.
6
SD6
Address bit 6 or Data bit 6.
5
SD5
Address bit 5 or Data bit 5.
4
SD4
Address bit 4 or Data bit 4.
3
SD3
Address bit 3 or Data bit 3.
2
SD2
Address bit 2 or Data bit 2.
AT89C51RE2
7663D–8051–10/08
AT89C51RE2
Bit
Number
Bit
Mnemonic Description
1
SD1
Address bit 1 or Data bit 1.
0
SD0
Address bit 0 (R/W) or Data bit 0.
Table 109. SSCS (094h) read - Synchronous Serial Control and Status Register
7
6
5
4
3
2
1
0
SC4
SC3
SC2
SC1
SC0
0
0
0
Table 110. SSCS Register: Read Mode - Reset Value = F8h
Bit
Number
Bit
Mnemonic Description
0
0
Always zero
1
0
Always zero
2
0
Always zero
3
SC0
4
SC1
5
SC2
Status Code bit 2
See to Table 106.
6
SC3
Status Code bit 3
See to Table 106.
7
SC4
Status Code bit 4
See to Table 106.
Status Code bit 0
See to Table 106.
Status Code bit 1
See to Table 106.
Table 111. SSADR (096h) - Synchronus Serial Address Register (read/write)
7
6
5
4
3
2
1
0
A7
A6
A5
A4
A3
A2
A1
A0
Table 112. SSADR Register - Reset value = FEh
Bit
Number
Bit
Mnemonic Description
7
A7
Slave Address bit 7
6
A6
Slave Address bit 6
5
A5
Slave Address bit 5
4
A4
Slave Address bit 4
3
A3
Slave Address bit 3
2
A2
Slave Address bit 2
1
A1
Slave Address bit 1
147
7663D–8051–10/08
Bit
Number
Bit
Mnemonic Description
General Call bit
0
GC
Clear to disable the general call address recognition.
Set to enable the general call address recognition.
148
AT89C51RE2
7663D–8051–10/08
AT89C51RE2
Serial Port
Interface (SPI)
The Serial Peripheral Interface Module (SPI) allows full-duplex, synchronous, serial communication between the MCU and peripheral devices, including other MCUs.
Features
Features of the SPI Module include the following:
•
Full-duplex, three-wire synchronous transfers
•
Master or Slave operation
•
Six programmable Master clock rates in master mode
•
Serial clock with programmable polarity and phase
•
Master Mode fault error flag with MCU interrupt capability
Signal Description Figure 56 shows a typical SPI bus configuration using one Master controller and many Slave
peripherals. The bus is made of three wires connecting all the devices.
Figure 56. SPI Master/Slaves Interconnection
Slave 1
MISO
MOSI
SCK
SS
MISO
MOSI
SCK
SS
VDD
Slave 4
Slave 3
MISO
MOSI
SCK
SS
0
1
2
3
MISO
MOSI
SCK
SS
MISO
MOSI
SCK
SS
PORT
Master
Slave 2
The Master device selects the individual Slave devices by using four pins of a parallel port to
control the four SS pins of the Slave devices.
Master Output Slave
Input (MOSI)
This 1-bit signal is directly connected between the Master Device and a Slave Device. 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 transmitted most
significant bit (MSB) first, least significant bit (LSB) last.
Master Input Slave
Output (MISO)
This 1-bit signal is directly connected between the Slave Device and a Master Device. The MISO
line is used to transfer data in series from the 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.
SPI Serial Clock (SCK)
This signal is used to synchronize the data transmission both in and out of the devices through
their MOSI and MISO lines. It is driven by the Master for eight clock cycles which allows to
exchange one Byte on the serial lines.
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 (SS high level) can drive the network.
The Master may select each Slave device by software through port pins (Figure 57). To prevent
bus conflicts on the MISO line, only one slave should be selected at a time by the Master for a
transmission.
149
7663E–8051–10/08
In a Master configuration, the SS line can be used in conjunction with the MODF flag in the SPI
Status register (SPSCR) 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 could be used as a general-purpose 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 SPSCR 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 includes 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 not to set SSDIS control bit when CPHA =’0’ because in this
mode, the SS is used to start the transmission.
Baud Rate
In Master mode, the baud rate can be selected from a baud rate generator which is controlled by
three bits in the SPCON register: SPR2, SPR1 and SPR0.The Master clock is selected from one
of seven clock rates resulting from the division of the internal clock by 4, 8, 16, 32, 64 or 128.
Table 113 gives the different clock rates selected by SPR2:SPR1:SPR0.
In Slave mode, the maximum baud rate allowed on the SCK input is limited to Fsys/4
Table 113. SPI Master Baud Rate Selection
150
SPR2
SPR1
SPR0
Clock Rate
Baud Rate Divisor (BD)
0
0
0
Don’t Use
No BRG
0
0
1
FCLK PERIPH /4
4
0
1
0
FCLK PERIPH/8
8
0
1
1
FCLK PERIPH /16
16
1
0
0
FCLK PERIPH /32
32
1
0
1
FCLK PERIPH /64
64
1
1
0
FCLK PERIPH /128
128
1
1
1
Don’t Use
No BRG
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Functional
Description
Figure 57 shows a detailed structure of the SPI Module.
Figure 57. SPI Module Block Diagram
Internal Bus
SPDAT
Transmit Data Register
Shift Register
7
6
5
4
3
2
1
0
Receive Data Register
SPSCR
SPIF
-
OVR
MODF SPTE
UARTM SPTEIE MODFIE
Clock
Logic
SPI
Control
SPCON
SPR2
SPEN SSDIS MSTR
CPOL
Pin
Control
Logic
CPHA
SPR1
SPR0
FCLK
PERIPH
M
S
MOSI
MISO
SCK
SS
SPI Interrupt
Request
8-bit bus
1-bit signal
Operating Modes
The Serial Peripheral Interface can be configured in one of the two modes: Master mode or
Slave mode. The configuration and initialization of the SPI Module is made through two
registers:
•
The Serial Peripheral Control register (SPCON)
•
The Serial Peripheral Status and Control Register (SPSCR)
Once the SPI is configured, the data exchange is made using:
•
The Serial Peripheral DATa register (SPDAT)
During an SPI transmission, data is simultaneously transmitted (shifted out serially) and
received (shifted in serially). A serial clock line (SCK) synchronizes shifting and sampling on the
two serial data lines (MOSI and MISO). A Slave Select line (SS) allows individual selection of a
Slave SPI device; Slave devices that are not selected do not interfere with SPI bus activities.
151
7663E–8051–10/08
When the Master device transmits data to the Slave device via the MOSI line, the Slave device
responds by sending data to the Master device via the MISO line. This implies full-duplex transmission with both data out and data in synchronized with the same clock (Figure 58).
Figure 58. Full-Duplex Master-Slave Interconnection
8-bit Shift register
SPI
Clock Generator
MISO
MISO
MOSI
MOSI
SCK
SS
Master MCU
8-bit Shift register
SCK
VDD
SS
VSS
Slave MCU
Master Mode
The SPI operates in Master mode when the Master bit, MSTR (1), in the SPCON register is set.
Only one Master SPI device can initiate transmissions. Software begins the transmission from a
Master SPI Module by writing to the Serial Peripheral Data Register (SPDAT). If the shift register
is empty, the Byte is immediately transferred to the shift register. The Byte begins shifting out on
MOSI pin under the control of the serial clock, SCK. Simultaneously, another Byte shifts in from
the Slave on the Master’s MISO pin. The transmission ends when the Serial Peripheral transfer
data flag, SPIF, in SPSCR becomes set. At the same time that SPIF becomes set, the received
Byte from the Slave is transferred to the receive data register in SPDAT. Software clears SPIF
by reading the Serial Peripheral Status register (SPSCR) with the SPIF bit set, and then reading
the SPDAT.
Slave Mode
The SPI operates in Slave mode when the Master bit, MSTR (2) , in the SPCON register is
cleared. Before a data transmission occurs, the Slave Select pin, SS, of the Slave device must
be set to’0’. SS must remain low until the transmission is complete.
In a Slave SPI Module, data enters the shift register under the control of the SCK from the Master SPI Module. After a Byte enters the shift register, it is immediately transferred to the receive
data register in SPDAT, and the SPIF bit is set. To prevent an overflow condition, Slave software
must then read the SPDAT before another Byte enters the shift register (3). A Slave SPI must
complete the write to the SPDAT (shift register) at least one bus cycle before the Master SPI
starts a transmission. If the write to the data register is late, the SPI transmits the data already in
the shift register from the previous transmission.
Transmission Formats
152
Software can select any of four combinations of serial clock (SCK) phase and polarity using two
bits in the SPCON: the Clock Polarity (CPOL (4)) and the Clock Phase (CPHA4). CPOL defines
the default SCK line level in idle state. It has no significant effect on the transmission format.
CPHA defines the edges on which the input data are sampled and the edges on which the output data are shifted (Figure 59 and Figure 60). The clock phase and polarity should be identical
for the Master SPI device and the communicating Slave device.
1.
The SPI Module should be configured as a Master before it is enabled (SPEN set). Also, the Master SPI should be configured before the Slave SPI.
2.
3.
4.
The SPI Module should be configured as a Slave before it is enabled (SPEN set).
The maximum frequency of the SCK for an SPI configured as a Slave is the bus clock speed.
Before writing to the CPOL and CPHA bits, the SPI should be disabled (SPEN =’0’).
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Figure 59. Data Transmission Format (CPHA = 0)
SCK Cycle Number
1
2
3
4
5
6
7
8
MSB
bit6
bit5
bit4
bit3
bit2
bit1
LSB
bit6
bit5
bit4
bit3
bit2
bit1
LSB
SPEN (Internal)
SCK (CPOL = 0)
SCK (CPOL = 1)
MOSI (from Master)
MISO (from Slave)
MSB
SS (to Slave)
Capture Point
Figure 60. Data Transmission Format (CPHA = 1)
1
2
3
4
5
6
7
8
MOSI (from Master)
MSB
bit6
bit5
bit4
bit3
bit2
bit1
LSB
MISO (from Slave)
MSB
bit6
bit5
bit4
bit3
bit2
bit1
SCK Cycle Number
SPEN (Internal)
SCK (CPOL = 0)
SCK (CPOL = 1)
LSB
SS (to Slave)
Capture Point
Figure 61. CPHA/SS Timing
MISO/MOSI
Byte 1
Byte 2
Byte 3
Master SS
Slave SS
(CPHA = 0)
Slave SS
(CPHA = 1)
As shown in Figure 59, the first SCK edge is the MSB capture strobe. Therefore, the Slave must
begin driving its data before the first SCK edge, and a falling edge on the SS pin is used to start
the transmission. The SS pin must be toggled high and then low between each Byte transmitted
(Figure 61).
Figure 60 shows an SPI transmission in which CPHA is’1’. In this case, the Master begins driving its MOSI pin on the first SCK edge. Therefore, the Slave uses the first SCK edge as a start
transmission signal. The SS pin can remain low between transmissions (Figure 61). This format
may be preferred in systems having only one Master and only one Slave driving the MISO data
line.
Queuing transmission
For an SPI configured in master or slave mode, a queued data byte must be transmitted/received immediately after the previous transmission has completed.
153
7663E–8051–10/08
When a transmission is in progress a new data can be queued and sent as soon as transmission
has been completed. So it is possible to transmit bytes without latency, useful in some
applications.
The SPTE bit in SPSCR is set as long as the transmission buffer is free. It means that the user
application can write SPDAT with the data to be transmitted until the SPTE becomes cleared.
Figure 62 shows a queuing transmission in master mode. Once the Byte 1 is ready, it is immediately sent on the bus. Meanwhile an other byte is prepared (and the SPTE is cleared), it will be
sent at the end of the current transmission. The next data must be ready before the end of the
current transmission.
Figure 62. Queuing Transmission In Master Mode
SCK
MOSI
MSB
B6
B5
B4
B3
B2
B1
LSB MSB
B6
B5
B4
B3
B2
B1
LSB
MISO
MSB
B6
B5
B4
B3
B2
B1
LSB MSB
B6
B5
B4
B3
B2
B1
LSB
Data
Byte 1
Byte 2
BYTE 1 under transmission
Byte 3
BYTE 2 under transmission
SPTE
In slave mode it is almost the same except it is the external master that start the transmission.
Also, in slave mode, if no new data is ready, the last value received will be the next data byte
transmitted.
154
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Error Conditions
The following flags in the SPSCR register indicate the SPI error conditions:
Mode Fault Error
(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.
•
Mode fault detection in Master mode:
MODF is set to warn that there may be a multi-master 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
Clearing the MODF bit is accomplished by a read of SPSCR 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.
Figure 63. Mode Fault Conditions in Master Mode (Cpha =’1’/Cpol =’0’)
0
1
2
1
z
0
MSB
B6
MISO
(from slave)
1
z
0
MSB
B6
SPI enable
1
z
0
SS
(master)
1
z
0
SS
(slave)
1
z
0
SCK cycle #
SCK
(from master)
MOSI
(from master)
•
0
3
1
z
0
MODF detected
Note:
0
B5
MODF detected
When SS is discarded (SS disabled) it is not possible to detect a MODF error in master mode
because the SPI is internally unselected and the SS pin is a general purpose I/O.
Mode fault detection in Slave mode
In slave mode, the MODF error is detected when SS goes high during a transmission.
A transmission begins when SS goes low and ends once the incoming SCK goes back to its idle
level following the shift of the eighteen data bit.
A MODF error occurs if a slave is selected (SS is low) and later unselected (SS is high) even if
no SCK is sent to that slave.
At any time, a’1’ on the SS pin of a slave SPI puts the MISO pin in a high impedance state and
internal state counter is cleared. Also, the slave SPI ignores all incoming SCK clocks, even if it
was already in the middle of a transmission. A new transmission will be performed as soon as
SS pin returns low.
155
7663E–8051–10/08
Figure 64. Mode Fault Conditions in Slave Mode
0
SCK cycle #
SCK
(from master)
MOSI
(from master)
0
OverRun Condition
2
3
4
MSB
B6
B5
B4
1
z
0
1
z
0
MISO
(from slave)
1
z
0
SS
(slave)
1
z
0
MSB
MSB
MODF detected
Note:
1
B6
MODF detected
when SS is discarded (SS disabled) it is not possible to detect a MODF error in slave mode
because the SPI is internally selected. Also the SS pin becomes a general purpose I/O.
This error mean that the speed is not adapted for the running application:
An OverRun condition occurs when a byte has been received whereas the previous one has not
been read by the application yet.
The last byte (which generate the overrun error) does not overwrite the unread data so that it
can still be read. Therefore, an overrun error always indicates the loss of data.
Interrupts
Three SPI status flags can generate a CPU interrupt requests:
Table 114. SPI Interrupts
Flag
Request
SPIF (SPI data transfer)
SPI Transmitter Interrupt Request
MODF (Mode Fault)
SPI mode-fault Interrupt Request
SPTE (Transmit register empty)
SPI transmit register empty Interrupt Request
Serial Peripheral data transfer flag, SPIF: This bit is set by hardware when a transfer has been
completed. SPIF bit generates transmitter CPU interrupt request only when SPTEIE is disabled.
Mode Fault flag, MODF: This bit is set to indicate that the level on the SS is inconsistent with the
mode of the SPI (in both master and slave modes).
Serial Peripheral Transmit Register empty flag, SPTE: This bit is set when the transmit buffer is
empty (other data can be loaded is SPDAT). SPTE bit generates transmitter CPU interrupt
request only when SPTEIE is enabled.
Note: While using SPTE interruption for “burst mode” transfers (SPTEIE=’1’), the user software application should take care to clear SPTEIE, during the last but one data reception (to
be able to generate an interrupt on SPIF flag at the end of the last data reception).
156
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Figure 65. SPI Interrupt Requests Generation
SPIF
SPTEIE
SPI
CPU Interrupt Request
SPTE
MODFIE
MODF
Registers
Three registers in the SPI module provide control, status and data storage functions. These registers are describe in the following paragraphs.
Serial Peripheral
Control Register
(SPCON)
•
The Serial Peripheral Control Register does the following:
•
Selects one of the Master clock rates
•
Configure the SPI Module as Master or Slave
•
Selects serial clock polarity and phase
•
Enables the SPI Module
•
Frees the SS pin for a general-purpose
Table 115 describes this register and explains the use of each bit
Table 115. SPCON Register
SPCON - Serial Peripheral Control Register (0D4H)
7
6
5
4
3
2
1
0
SPR2
SPEN
SSDIS
MSTR
CPOL
CPHA
SPR1
SPR0
Bit Number
Bit Mnemonic
7
SPR2
6
SPEN
Description
Serial Peripheral Rate 2
Bit with SPR1 and SPR0 define the clock rate (See bits SPR1 and SPR0 for
detail).
Serial Peripheral Enable
Cleared to disable the SPI interface (internal reset of the SPI).
Set to enable the SPI interface.
SS Disable
Cleared to enable SS in both Master and Slave modes.
5
SSDIS
4
MSTR
Set to disable SS in both Master and Slave modes. In Slave mode, this bit
has no effect if CPHA =’0’. When SSDIS is set, no MODF interrupt request
is generated.
Serial Peripheral Master
Cleared to configure the SPI as a Slave.
Set to configure the SPI as a Master.
157
7663E–8051–10/08
Bit Number
Bit Mnemonic
3
CPOL
Description
Clock Polarity
Cleared to have the SCK set to’0’ in idle state.
Set to have the SCK set to’1’ in idle state.
Clock Phase
2
Cleared to have the data sampled when the SCK leaves the idle state (see
CPOL).
CPHA
Set to have the data sampled when the SCK returns to idle state (see
CPOL).
1
SPR1
0
SPR0
SPR2
SPR1
0
0
SPR0 Serial Peripheral Rate
0
0
0
1
FCLK PERIPH /4
0
1
0
FCLK PERIPH /8
0
1
1
FCLK PERIPH /16
1
0
0
FCLK PERIPH /32
1
0
1
FCLK PERIPH /64
1
1
0
FCLK PERIPH /128
1
1
1
Invalid
Invalid
Reset Value = 0001 0100b
Not bit addressable
Serial Peripheral Status
Register and Control
(SPSCR)
The Serial Peripheral Status Register contains flags to signal the following conditions:
•
Data transfer complete
•
Write collision
•
Inconsistent logic level on SS pin (mode fault error)
Table 116. SPSCR Register
SPSCR - Serial Peripheral Status and Control register (C4H)
7
6
5
4
3
2
1
0
SPIF
-
OVR
MODF
SPTE
UARTM
SPTEIE
MODFIE
Bit Number
Bit
Mnemonic
Description
Serial Peripheral Data Transfer Flag
7
SPIF
Cleared by hardware to indicate data transfer is in progress or has been approved by a
clearing sequence.
Set by hardware to indicate that the data transfer has been completed.
This bit is cleared when reading or writing SPDATA after reading SPSCR.
6
-
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Overrun Error Flag
5
OVR
- Set by hardware when a byte is received whereas SPIF is set (the previous received
data is not overwritten).
- Cleared by hardware when reading SPSCR
158
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Bit Number
Bit
Mnemonic
Description
Mode Fault
- Set by hardware to indicate that the SS pin is in inappropriate logic level (in both master
and slave modes).
- Cleared by hardware when reading SPSCR
4
MODF
When MODF error occurred:
- In slave mode: SPI interface ignores all transmitted data while SS remains high. A new
transmission is perform as soon as SS returns low.
- In master mode: SPI interface is disabled (SPEN=0, see description for SPEN bit in
SPCON register).
Serial Peripheral Transmit register Empty
3
SPTE
- Set by hardware when transmit register is empty (if needed, SPDAT can be loaded with
another data).
- Cleared by hardware when transmit register is full (no more data should be loaded in
SPDAT).
Serial Peripheral UART mode
2
UARTM
Set and cleared by software:
- Clear: Normal mode, data are transmitted MSB first (default)
- Set: UART mode, data are transmitted LSB first.
Interrupt Enable for SPTE
Set and cleared by software:
1
SPTEIE
- Set to enable SPTE interrupt generation (when SPTE goes high, an interrupt is
generated).
- Clear to disable SPTE interrupt generation
Caution: When SPTEIE is set no interrupt generation occurred when SPIF flag goes high.
To enable SPIF interrupt again, SPTEIE should be cleared.
Interrupt Enable for MODF
0
MODFIE
Set and cleared by software:
- Set to enable MODF interrupt generation
- Clear to disable MODF interrupt generation
Reset Value = 00X0 XXXXb
Not Bit addressable
Serial Peripheral DATa
Register (SPDAT)
The Serial Peripheral Data Register (Table 117) is a read/write buffer for the receive data register. A write to SPDAT places data directly into the shift register. No transmit buffer is available in
this model.
A Read of the SPDAT returns the value located in the receive buffer and not the content of the
shift register.
Table 117. SPDAT Register
SPDAT - Serial Peripheral Data Register (C5H)
7
6
5
4
3
2
1
0
R7
R6
R5
R4
R3
R2
R1
R0
Reset Value = Indeterminate
R7:R0: Receive data bits
159
7663E–8051–10/08
SPCON, SPSTA and SPDAT registers may be read and written at any time while there is no ongoing exchange. However, special care should be taken when writing to them while a transmission is on-going:
160
•
Do not change SPR2, SPR1 and SPR0
•
Do not change CPHA and CPOL
•
Do not change MSTR
•
Clearing SPEN would immediately disable the peripheral
•
Writing to the SPDAT will cause an overflow.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Power Monitor
The POR/PFD function monitors the internal power-supply of the CPU core memories and the
peripherals, and if needed, suspends their activity when the internal power supply falls below a
safety threshold. This is achieved by applying an internal reset to them.
By generating the Reset the Power Monitor insures a correct start up when AT89C51RE2 is
powered up.
Description
In order to startup and maintain the microcontroller in correct operating mode, VCC has to be stabilized in the VCC operating range and the oscillator has to be stabilized with a nominal amplitude
compatible with logic level VIH/VIL.
These parameters are controlled during the three phases: power-up, normal operation and
power going down. See Figure 66.
Figure 66. Power Monitor Block Diagram
VCC
CPU core
Power On Reset
Power Fail Detect
Voltage Regulator
Regulated
Supply
Memories
Peripherals
XTAL1
(1)
Internal Reset
RST pin
PCA
Watchdog
Note:
Hardware
Watchdog
1. Once XTAL1 High and low levels reach above and below VIH/VIL. a 1024 clock period delay
will extend the reset coming from the Power Fail Detect. If the power falls below the Power Fail
Detect threshold level, the Reset will be applied immediately.
The Voltage regulator generates a regulated internal supply for the CPU core the memories and
the peripherals. Spikes on the external Vcc are smoothed by the voltage regulator.
161
7663E–8051–10/08
The Power fail detect monitor the supply generated by the voltage regulator and generate a
reset if this supply falls below a safety threshold as illustrated in the Figure 67 below.
Figure 67. Power Fail Detect
Vcc
t
Reset
Vcc
When the power is applied, the Power Monitor immediately asserts a reset. Once the internal
supply after the voltage regulator reach a safety level, the power monitor then looks at the XTAL
clock input. The internal reset will remain asserted until the Xtal1 levels are above and below
VIH and VIL. Further more. An internal counter will count 1024 clock periods before the reset is
de-asserted.
If the internal power supply falls below a safety level, a reset is immediately asserted.
162
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Power-off Flag
The power-off flag allows the user to distinguish between a “cold start” reset and a “warm start”
reset.
A cold start reset is the one induced by VCC switch-on. A warm start reset occurs while VCC is still
applied to the device and could be generated for example by an exit from power-down.
The power-off flag (POF) is located in PCON register (Table 118). POF is set by hardware when
VCC rises from 0 to its nominal voltage. The POF can be set or cleared by software allowing the
user to determine the type of reset.
Table 118. PCON Register
PCON - Power Control Register (87h)
7
6
5
4
3
2
1
0
SMOD1
SMOD0
-
POF
GF1
GF0
PD
IDL
Bit
Bit
Number
Mnemonic
7
SMOD1
Serial port Mode bit 1
Set to select double baud rate in mode 1, 2 or 3.
6
SMOD0
Serial port Mode bit 0
Cleared to select SM0 bit in SCON register.
Set to select FE bit in SCON register.
5
-
Description
Reserved
The value read from this bit is indeterminate. Do not set this bit.
4
POF
Power-Off Flag
Cleared to recognize next reset type.
Set by hardware when VCC rises from 0 to its nominal voltage. Can also be set by
software.
3
GF1
General purpose Flag
Cleared by user for general purpose usage.
Set by user for general purpose usage.
2
GF0
General purpose Flag
Cleared by user for general purpose usage.
Set by user for general purpose usage.
1
PD
Power-Down mode bit
Cleared by hardware when reset occurs.
Set to enter power-down mode.
0
IDL
Idle mode bit
Cleared by hardware when interrupt or reset occurs.
Set to enter idle mode.
Reset Value = 00X1 0000b
Not bit addressable
163
7663E–8051–10/08
Reset
Introduction
The reset sources are: Power Management, Hardware Watchdog, PCA Watchdog and Reset
input.
Figure 68. Reset schematic
Power
Monitor
Hardware
Watchdog
Internal Reset
PCA
Watchdog
RST
Reset Input
The Reset input can be used to force a reset pulse longer than the internal reset controlled by
the Power Monitor. RST input has a pull-down resistor allowing power-on reset by simply connecting an external capacitor to V CC as shown in Figure 69. Resistor value and input
characteristics are discussed in the Section “DC Characteristics” of the AT89C51RE2 datasheet.
Figure 69. Reset Circuitry and Power-On Reset
VDD
To internal reset
RST
R
RST
+
RST
VSS
a. RST input circuitry
164
b. Power-on Reset
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Reset Output
As detailed in Section “Hardware Watchdog Timer”, page 124, the WDT generates a 96-clock
period pulse on the RST pin. In order to properly propagate this pulse to the rest of the application in case of external capacitor or power-supply supervisor circuit, a 1 kΩ resistor must be
added as shown Figure 70.
Figure 70. Recommended Reset Output Schematic
VDD
+
RST
VDD
1K
RST
VSS
To other
on-board
circuitry
165
7663E–8051–10/08
Electrical Characteristics
Absolute Maximum Ratings
Note:
I = industrial ........................................................-40°C to 85°C
Storage Temperature .................................... -65°C to + 150°C
Voltage on VCC to VSS (standard voltage) .........-0.5V to + 6.5V
Voltage on VCC to VSS (low voltage)..................-0.5V to + 4.5V
Voltage on Any Pin to VSS ..........................-0.5V to VCC + 0.5V
Power Dissipation ........................................................... 1 W(2)
Stresses at or above 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 above those indicated in the operational
sections of this specification is not implied. Exposure
to absolute maximum rating conditions may affect
device reliability.
Power dissipation is based on the maximum allowable die temperature and the thermal resistance of
the package.
DC Parameters
TA = -40°C to +85°C; VSS = 0V; VCC =2.7V to 5.5V; F = 0 to 40 MHz
Symbol
Parameter
Min
VIL
Input Low Voltage
VIH
Input High Voltage except RST, XTAL1
VIH1
Input High Voltage RST, XTAL1
Typ
Max
Unit
Test Conditions
-0.5
0.2 VCC - 0.1
V
0.2 VCC + 0.9
VCC + 0.5
V
0.7 VCC
VCC + 0.5
V
0.3
V
IOL = 100 μA(4)
0.45
V
IOL = 1.6 mA(4)
1.0
V
IOL = 3.5 mA(4)
0.45
V
IOL = 0.8 mA(4)
0.3
V
IOL = 200 μA(4)
0.45
V
IOL = 3.2 mA(4)
1.0
V
IOL = 7.0 mA(4)
0.45
V
IOL = 1.6 mA(4)
VCC - 0.3
V
IOH = -10 μA
VCC - 0.7
V
IOH = -30 μA
VCC - 1.5
V
IOH = -60 μA
0.9 VCC
V
IOH = -10 μA
VCC - 0.3
V
IOH = -200 μA
VCC - 0.7
V
IOH = -3.2 mA
VCC - 1.5
V
IOH = -7.0 mA
0.9 VCC
V
IOH = -10 μA
VCC = 4.5V to 5.5V
VOL
Output Low Voltage, ports 1, 2, 3, 4 (6)
VCC = 2.7V to 5.5V
VCC = 4.5V to 5.5V
VOL1
Output Low Voltage, port 0, ALE, PSEN (6)
VCC = 2.7V to 5.5V
VCC = 5V ± 10%
VOH
Output High Voltage, ports 1, 2, 3, 4
VCC = 2.7V to 5.5V
VCC = 5V ± 10%
VOH1
Output High Voltage, port 0, ALE, PSEN
VCC = 2.7V to 5.5V
166
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
TA = -40°C to +85°C; VSS = 0V; VCC =2.7V to 5.5V; F = 0 to 40 MHz (Continued)
Symbol
RRST
Parameter
Min
Typ
Max
Unit
50
200(5)
250
kΩ
RST Pull-down Resistor
Test Conditions
IIL
Logical 0 Input Current ports 1, 2, 3, 4 and 5
-50
μA
VIN = 0.45V
ILI
Input Leakage Current
±10
μA
0.45V < VIN < VCC
ITL
Logical 1 to 0 Transition Current, ports 1, 2, 3, 4
-650
μA
VIN = 2.0V
CIO
Capacitance of I/O Buffer
10
pF
FC = 3 MHz
TA = 25°C
IPD
Power-down Current
150
μA
2.7 < VCC < 5.5V(3)
75
ICCOP
Power Supply Current on normal mode
0.4 x Frequency (MHz) + 5
mA
VCC = 5.5V(1)
ICCIDLE
Power Supply Current on idle mode
0.3 x Frequency (MHz) + 5
mA
VCC = 5.5V(2)
ICCWRITE
Power Supply Current on flash write
0.8 x Frequency (MHz) + 15
mA
VCC = 5.5V
10
ms
2.7 < VCC < 5.5V
tWRITE
Notes:
Flash programming time
7
1. Operating ICC is measured with all output pins disconnected; XTAL1 driven with TCLCH, TCHCL = 5 ns (see Figure 74), VIL =
VSS + 0.5V, VIH = VCC - 0.5V; XTAL2 N.C.; EA = RST = Port 0 = VCC. ICC would be slightly higher if a crystal oscillator used
(see Figure 71).
2. Idle ICC is measured with all output pins disconnected; XTAL1 driven with TCLCH, TCHCL = 5 ns, VIL = VSS + 0.5V, VIH = VCC 0.5V; XTAL2 N.C; Port 0 = VCC; EA = RST = VSS (see Figure 72).
3. Power-down ICC is measured with all output pins disconnected; EA = VCC, PORT 0 = VCC; XTAL2 NC.; RST = VSS (see Figure 73).
4. Capacitance loading on Ports 0 and 2 may cause spurious noise pulses to be superimposed on the VOLS of ALE and Ports 1
and 3. The noise is due to external bus capacitance discharging into the Port 0 and Port 2 pins when these pins make 1 to 0
transitions during bus operation. In the worst cases (capacitive loading 100 pF), the noise pulse on the ALE line may exceed
0.45V with maxi VOL peak 0.6V. A Schmitt Trigger use is not necessary.
5. Typical values are based on a limited number of samples and are not guaranteed. The values listed are at room temperature
and 5V.
6. Under steady state (non-transient) conditions, IOL must be externally limited as follows:
Maximum IOL per port pin: 10 mA
Maximum IOL per 8-bit port:
Port 0: 26 mA
Ports 1, 2 and 3: 15 mA
Maximum total IOL for all output pins: 71 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.
Figure 71. ICC Test Condition, Active Mode
VCC
ICC
VCC
P0
VCC
RST
(NC)
CLOCK
SIGNAL
VCC
EA
XTAL2
XTAL1
VSS
All other pins are disconnected.
167
7663E–8051–10/08
Figure 72. ICC Test Condition, Idle Mode
VCC
ICC
VCC
VCC
P0
RST
EA
XTAL2
XTAL1
VSS
(NC)
CLOCK
SIGNAL
All other pins are disconnected.
Figure 73. ICC Test Condition, Power-down Mode
VCC
ICC
VCC
VCC
P0
RST
(NC)
EA
XTAL2
XTAL1
VSS
All other pins are disconnected.
Figure 74. Clock Signal Waveform for ICC Tests in Active and Idle Modes
VCC-0.5V
0.45V
TCLCH
TCHCL
TCLCH = TCHCL = 5ns.
0.7VCC
0.2VCC-0.1
AC Parameters
Explanation of the AC
Symbols
Each timing symbol has 5 characters. The first character is always a “T” (stands for time). The
other characters, depending on their positions, stand for the name of a signal or the logical status of that signal. The following is a list of all the characters and what they stand for.
Example:TAVLL = Time for Address Valid to ALE Low.
TLLPL = Time for ALE Low to PSEN Low.
(Load Capacitance for port 0, ALE and PSEN = 100 pF; Load Capacitance for all other outputs =
80 pF.)
Table 119 Table 122, and Table 125 give the description of each AC symbols.
Table 120, Table 121, Table 123 and Table 126 gives the range for each AC parameter.
Table 120, Table 121 and Table 127 give the frequency derating formula of the AC parameter
for each speed range description. To calculate each AC symbols. Take the x value in the corresponding column (-M or -L) and use this value in the formula.
168
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Example: TLLIU for -M and 20 MHz, Standard clock.
x = 35 ns
T 50 ns
TCCIV = 4T - x = 165 ns
External Program
Memory
Characteristics
Table 119. Symbol Description
Symbol
Parameter
T
Oscillator clock period
TLHLL
ALE pulse width
TAVLL
Address Valid to ALE
TLLAX
Address Hold After ALE
TLLIV
ALE to Valid Instruction In
TLLPL
ALE to PSEN
TPLPH
PSEN Pulse Width
TPLIV
PSEN to Valid Instruction In
TPXIX
Input Instruction Hold After PSEN
TPXIZ
Input Instruction Float After PSEN
TAVIV
Address to Valid Instruction In
TPLAZ
PSEN Low to Address Float
Table 120. AC Parameters for a Fix Clock
-M(1)
Symbol
Min
Max
Min
Units
Max
T
25
25
ns
TLHLL
35
35
ns
TAVLL
5
5
ns
TLLAX
5
5
ns
n 65
TLLIV
65
ns
TLLPL
5
5
ns
TPLPH
50
50
ns
TPLIV
TPXIX
Notes:
-L(2)
30
0
30
0
ns
ns
TPXIZ
10
10
ns
TAVIV
80
80
ns
TPLAZ
10
10
ns
1. ‘ -L ‘ refers to 2V - 5.5V version.
2. ‘ -M ’ refers to 4.5V to 5.5V version.
169
7663E–8051–10/08
Table 121. AC Parameters for a Variable Clock
Symbol
Type
Standard
Clock
X2 Clock
X parameter for
-M(1) range
X parameter for
-L(2) range
Units
TLHLL
Min
2T-x
T-x
15
15
ns
TAVLL
Min
T-x
0.5 T - x
20
20
ns
TLLAX
Min
T-x
0.5 T - x
20
20
ns
TLLIV
Max
4T-x
2T-x
35
35
ns
TLLPL
Min
T-x
0.5 T - x
15
15
ns
TPLPH
Min
3T-x
1.5 T - x
25
25
ns
TPLIV
Max
3T-x
1.5 T - x
45
45
ns
TPXIX
Min
x
x
0
0
ns
TPXIZ
Max
T-x
0.5 T - x
15
15
ns
TAVIV
Max
5T-x
2.5 T - x
45
45
ns
TPLAZ
Max
x
x
10
10
ns
Notes:
170
1. ‘ -L ‘ refers to 2V - 5.5V version.
2. ‘ -M ’ refers to 4.5V to 5.5V version.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
External Program
Memory Read Cycle
12 TCLCL
TLHLL
TLLIV
ALE
TLLPL
TPLPH
PSEN
TLLAX
TAVLL
PORT 0
INSTR IN
TPXAV
TPXIZ
TPLIV
TPLAZ
A0-A7
TPXIX
INSTR IN
A0-A7
INSTR IN
TAVIV
PORT 2
External Data Memory
Characteristics
ADDRESS
OR SFR-P2
ADDRESS A8-A15
ADDRESS A8-A15
Table 122. Symbol Description
Symbol
Parameter
TRLRH
RD Pulse Width
TWLWH
WR Pulse Width
TRLDV
RD to Valid Data In
TRHDX
Data Hold After RD
TRHDZ
Data Float After RD
TLLDV
ALE to Valid Data In
TAVDV
Address to Valid Data In
TLLWL
ALE to WR or RD
TAVWL
Address to WR or RD
TQVWX
Data Valid to WR Transition
TQVWH
Data Set-up to WR High
TWHQX
Data Hold After WR
TRLAZ
RD Low to Address Float
TWHLH
RD or WR High to ALE high
171
7663E–8051–10/08
Table 123. AC Parameters for a Fix Clock
-M(1)
Symbol
Min
TRLRH
125
125
ns
TWLWH
125
125
ns
TRHDX
Max
Min
95
TRLDV
0
Max
95
0
Units
ns
ns
TRHDZ
25
25
ns
TLLDV
155
155
ns
TAVDV
160
160
ns
105
ns
TLLWL
45
TAVWL
70
70
ns
TQVWX
5
5
ns
TQVWH
155
155
ns
TWHQX
10
10
ns
TRLAZ
0
0
ns
TWHLH
5
Notes:
172
-L(2)
105
45
45
5
45
ns
1. ‘ -L ‘ refers to 2V - 5.5V version.
2. ‘ -M ’ refers to 4.5V to 5.5V version.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 124. AC Parameters for a Variable Clock
Symbol
Type
Standard
Clock
X2 Clock
X parameter for
-M(1) range
X parameter for
-L(2) range
Units
TRLRH
Min
6T-x
3T-x
25
25
ns
TWLWH
Min
6T-x
3T-x
25
25
ns
TRLDV
Max
5T-x
2.5 T - x
30
30
ns
TRHDX
Min
x
x
0
0
ns
TRHDZ
Max
2T-x
T-x
25
25
ns
TLLDV
Max
8T-x
4T -x
45
45
ns
TAVDV
Max
9T-x
4.5 T - x
65
65
ns
TLLWL
Min
3T-x
1.5 T - x
30
30
ns
TLLWL
Max
3T+x
1.5 T + x
30
30
ns
TAVWL
Min
4T-x
2T-x
30
30
ns
TQVWX
Min
T-x
0.5 T - x
20
20
ns
TQVWH
Min
7T-x
3.5 T - x
20
20
ns
TWHQX
Min
T-x
0.5 T - x
15
15
ns
TRLAZ
Max
x
x
0
0
ns
TWHLH
Min
T-x
0.5 T - x
20
20
ns
TWHLH
Max
T+x
0.5 T + x
20
20
ns
Notes:
1. ‘ -L ‘ refers to 2V - 5.5V version.
2. ‘ -M ’ refers to 4.5V to 5.5V version.
External Data Memory
Write Cycle
TWHLH
ALE
PSEN
TLLWL
TWLWH
WR
TLLAX
PORT 0
A0-A7
TQVWX
TQVWH
TWHQX
DATA OUT
TAVWL
PORT 2
ADDRESS
OR SFR-P2
ADDRESS A8-A15 OR SFR P2
173
7663E–8051–10/08
External Data Memory Read Cycle
TWHLH
TLLDV
ALE
PSEN
TLLWL
TRLRH
RD
TRHDZ
TAVDV
TLLAX
PORT 0
TRHDX
A0-A7
DATA IN
TRLAZ
TAVWL
PORT 2
Serial Port Timing Shift Register Mode
ADDRESS
OR SFR-P2
ADDRESS A8-A15 OR SFR P2
Table 125. Symbol Description
Symbol
Parameter
TXLXL
Serial port clock cycle time
TQVHX
Output data set-up to clock rising edge
TXHQX
Output data hold after clock rising edge
TXHDX
Input data hold after clock rising edge
TXHDV
Clock rising edge to input data valid
Table 126. AC Parameters for a Fix Clock
-M(1)
Symbol
Min
TXLXL
300
300
ns
TQVHX
200
200
ns
TXHQX
30
30
ns
TXHDX
0
0
ns
TXHDV
Notes:
174
-L(2)
Max
117
Min
Max
117
Units
ns
1. ‘ -L ‘ refers to 2V - 5.5V version.
2. ‘ -M ’ refers to 4.5V to 5.5V version.
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Table 127. AC Parameters for a Variable Clock
Symbol
Type
Standard
Clock
X2 Clock
TXLXL
Min
12 T
6T
TQVHX
Min
10 T - x
5T-x
50
50
ns
TXHQX
Min
2T-x
T-x
20
20
ns
TXHDX
Min
x
x
0
0
ns
TXHDV
Max
10 T - x
5 T- x
133
133
ns
Notes:
X Parameter For
-M(1) Range
X Parameter For
-L(2) Range
Units
ns
1. ‘ -L ‘ refers to 2V - 5.5V version.
2. ‘ -M ’ refers to 4.5V to 5.5V version.
Shift Register Timing
Waveforms
INSTRUCTION
0
1
2
3
4
5
6
7
8
ALE
TXLXL
CLOCK
TXHQX
TQVXH
0
OUTPUT DATA
WRITE to SBUF
1
2
4
5
6
7
TXHDX
TXHDV
INPUT DATA
3
VALID
VALID
VALID
SET TI
VALID
VALID
VALID
VALID
SET RI
CLEAR RI
External Clock Drive
Waveforms
VALID
VCC-0.5V
0.45V
0.7VCC
0.2VCC-0.1
TCHCL
TCHCX
TCLCH
TCLCX
TCLCL
AC Testing
Input/Output
Waveforms
VCC -0.5V
0.2 VCC + 0.9
INPUT/OUTPUT
0.2 VCC - 0.1
0.45V
AC inputs during testing are driven at VCC - 0.5 for a logic “1” and 0.45V for a logic “0”. Timing
measurement are made at VIH min. for a logic “1” and VIL max for a logic “0”.
Float Waveforms
FLOAT
VOH - 0.1V
VOL + 0.1V
VLOAD
VLOAD + 0.1V
VLOAD - 0.1V
175
7663E–8051–10/08
For timing purposes as port pin is no longer floating when a 100 mV change from load voltage
occurs and begins to float when a 100 mV change from the loaded VOH/VOL level occurs. IOL/IOH
≥ ± 20 mA.
Clock Waveforms
Valid in normal clock mode. In X2 mode XTAL2 must be changed to XTAL2/2.
Figure 75. Internal Clock Signals
INTERNAL
CLOCK
STATE4
STATE5
STATE6
STATE1
STATE2
STATE3
STATE4
STATE5
P1
P1
P1
P1
P1
P1
P1
P1
P2
P2
P2
P2
P2
P2
P2
P2
XTAL2
ALE
THESE SIGNALS ARE NOT ACTIVATED DURING THE
EXECUTION OF A MOVX INSTRUCTION
EXTERNAL PROGRAM MEMORY FETCH
PSEN
P0
DATA
SAMPLED
FLOAT
P2 (EXT)
PCL OUT
DATA
SAMPLED
FLOAT
PCL OUT
DATA
SAMPLED
FLOAT
PCL OUT
INDICATES ADDRESS TRANSITIONS
READ CYCLE
RD
PCL OUT (IF PROGRAM
MEMORY IS EXTERNAL)
P0
DPL OR Rt OUT
DATA
SAMPLED
FLOAT
INDICATES DPH OR P2 SFR TO PCH TRANSITION
P2
WRITE CYCLE
WR
P0
PCL OUT (EVEN IF PROGRAM
MEMORY IS INTERNAL)
DPL OR Rt OUT
PCL OUT (IF PROGRAM
MEMORY IS EXTERNAL)
DATA OUT
P2
INDICATES DPH OR P2 SFR TO PCH TRANSITION
PORT OPERATION
OLD DATA NEW DATA
MOV PORT SRC
P0 PINS SAMPLED
P0 PINS SAMPLED
MOV DEST P0
MOV DEST PORT (P1. P2. P3)
(INCLUDES INTO. INT1. TO T1)
SERIAL PORT SHIFT CLOCK
P1, P2, P3 PINS SAMPLED
RXD SAMPLED
P1, P2, P3 PINS SAMPLED
RXD SAMPLED
TXD (MODE 0)
This diagram indicates when signals are clocked internally. The time it takes the signals to propagate to the pins, however,
ranges from 25 to 125 ns. This propagation delay is dependent on variables such as temperature and pin loading. Propagation also varies from output to output and component. Typically though (TA = 25°C fully loaded) RD and WR propagation
delays are approximately 50 ns. The other signals are typically 85 ns. Propagation delays are incorporated in the AC
specifications.
176
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Flash Memory
Table 128. Timing Symbol Definitions
Signals
Conditions
S (Hardware
condition)
PSEN#,EA
L
Low
R
RST
V
Valid
B
FBUSY flag
X
No Longer Valid
Table 129. Memory AC Timing
VDD = 3V to 5.5V, TA = -40 to +85°C
Symbol
Parameter
Min
Typ
TSVRL
Input PSEN# Valid to RST Edge
50
ns
TRLSX
Input PSEN# Hold after RST Edge
50
ns
TBHBL
Flash Internal Busy (Programming) Time
NFCY
Number of Flash Erase/Write Cycles
TFDR
Flash Retention Time
10
Max
Unit
ms
100 000
cycles
10
years
Figure 76. Flash Memory – ISP Waveforms
RST
TSVRL
TRLSX
PSEN#1
Figure 77. Flash Memory – Internal Busy Waveforms
FBUSY bit
TBHBL
177
7663E–8051–10/08
Ordering Information
Table 130. Possible Order Entries
Part Number
Supply Voltage
Temperature Range
2.7V-5.5V
Industrial & Green
AT89C51RE2-SLSUM
PLCC44
AT89C51RE2-RLTUM
VQFP44
AT89C51RE2-SLSEM
PLCC44
2.7V-5.5V
AT89C51RE2-RLTEM
178
Package
Engineering Samples
VQFP44
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Packaging Information
PLCC44
179
7663E–8051–10/08
STANDARD NOTES FOR PLCC
1/ CONTROLLING DIMENSIONS : INCHES
2/ DIMENSIONING AND TOLERANCING PER ANSI Y 14.5M - 1982.
3/ "D" AND "E1" DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTUSIONS.
MOLD FLASH OR PROTUSIONS SHALL NOT EXCEED 0.20 mm (.008 INCH) PER
SIDE.
180
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
VQFP44
181
7663E–8051–10/08
STANDARD NOTES FOR PQFP/ VQFP / TQFP / DQFP
1/ CONTROLLING DIMENSIONS : INCHES
2/ ALL DIMENSIONING AND TOLERANCING CONFORM TO ANSI Y 14.5M 1982.
3/ "D1 AND E1" DIMENSIONS DO NOT INCLUDE MOLD PROTUSIONS.
MOLD PROTUSIONS SHALL NOT EXCEED 0.25 mm (0.010 INCH).
THE TOP PACKAGE BODY SIZE MAY BE SMALLER THAN THE BOTTOM
PACKAGE BODY SIZE BY AS MUCH AS 0.15 mm.
4/ DATUM PLANE "H" LOCATED AT MOLD PARTING LINE AND
COINCIDENT WITH LEAD, WHERE LEAD EXITS PLASTIC BODY AT
BOTTOM OF PARTING LINE.
5/ DATUM "A" AND "D" TO BE DETERMINED AT DATUM PLANE H.
6/ DIMENSION " f " DOES NOT INCLUDE DAMBAR PROTUSION ALLOWABLE
DAMBAR PROTUSION SHALL BE 0.08mm/.003" TOTAL IN EXCESS OF THE
" f " DIMENSION AT MAXIMUM MATERIAL CONDITION .
DAMBAR CANNOT BE LOCATED ON THE LOWER RADIUS OR THE FOOT.
182
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Document
Revision
History
Changes from
7663B to 7663C
1. Modified ordering information.
Changes from
7663C to 7663D
1. TWI interface added.
Changes from
7663D to 7663E
1. Removed 64 and 68 pins package product version.
2. Various grammatical corections throughout document.
2. Minor correction on Table 69 on page 102.
183
7663E–8051–10/08
Features ................................................................................................. 1
Description ............................................................................................ 2
Block Diagram ...................................................................................... 3
Pin Configurations ............................................................................... 4
SFR Mapping ......................................................................................... 7
Enhanced Features ............................................................................ 13
X2 Feature .......................................................................................................... 13
Dual Data Pointer Register DPTR ..................................................... 18
Memory Architecture ........................................................................................... 21
Expanded RAM (XRAM) ..................................................................... 22
Registers............................................................................................................. 24
Extended Stack................................................................................................... 25
Flash Memory ..................................................................................... 27
General Description ............................................................................................
Features..............................................................................................................
Flash memory organization ................................................................................
On-Chip Flash memory.......................................................................................
On-Chip ROM bootloader ...................................................................................
Boot process.......................................................................................................
Access and Operations Descriptions..................................................................
27
27
27
28
31
32
36
Operation Cross Memory Access ..................................................... 50
Sharing Instructions ........................................................................... 50
Flash Protection from Parallel Programming .................................. 52
Bootloader Architecture .................................................................... 53
Introduction .........................................................................................................
Bootloader Description .......................................................................................
ISP Protocol Description.....................................................................................
Protocol...............................................................................................................
ISP Commands description ................................................................................
53
54
56
57
61
Timers/Counters ................................................................................. 68
Timer/Counter Operations .................................................................................. 68
Timer 0................................................................................................................ 68
Timer 1................................................................................................................ 71
1
AT89C51RE2
7663E–8051–10/08
AT89C51RE2
Interrupt .............................................................................................................. 71
Registers............................................................................................................. 73
Timer 2 ................................................................................................. 77
Auto-Reload Mode.............................................................................................. 77
Programmable Clock-Output .............................................................................. 78
Registers............................................................................................................. 80
Programmable Counter Array PCA ................................................... 82
PCA Capture Mode.............................................................................................
16-bit Software Timer/ Compare Mode...............................................................
High Speed Output Mode ...................................................................................
Pulse Width Modulator Mode..............................................................................
PCA Watchdog Timer .........................................................................................
90
90
91
92
93
Serial I/O Port ...................................................................................... 94
Framing Error Detection ..................................................................................... 94
Automatic Address Recognition.......................................................................... 95
Registers............................................................................................................. 97
Baud Rate Selection for UART 0 for Mode 1 and 3............................................ 98
Baud Rate Selection for UART 1 for Mode 1 and 3............................................ 99
UART Registers................................................................................................ 103
Interrupt System ............................................................................... 109
Registers........................................................................................................... 110
Interrupt Sources and Vector Addresses.......................................................... 117
Power Management .......................................................................... 118
Introduction .......................................................................................................
Idle Mode ..........................................................................................................
Power-Down Mode ...........................................................................................
Registers...........................................................................................................
118
118
118
121
Oscillator ........................................................................................... 122
Registers........................................................................................................... 122
Functional Block Diagram .................................................................................123
Hardware Watchdog Timer .............................................................. 124
Using the WDT ................................................................................................. 124
WDT During Power Down and Idle................................................................... 125
Reduced EMI Mode ........................................................................... 126
Keyboard Interface ........................................................................... 127
Registers........................................................................................................... 128
2
7663E–8051–10/08
2-wire Interface (TWI) ....................................................................... 131
Description........................................................................................................ 133
Notes ................................................................................................................ 136
Registers........................................................................................................... 146
Serial Port Interface (SPI) ................................................................ 149
Features............................................................................................................ 149
Signal Description............................................................................................. 149
Functional Description ...................................................................................... 151
Power Monitor ................................................................................... 161
Description........................................................................................................ 161
Power-off Flag ................................................................................... 163
Reset .................................................................................................. 164
Introduction ....................................................................................................... 164
Reset Input ....................................................................................................... 164
Reset Output .....................................................................................................165
Electrical Characteristics ................................................................. 166
Absolute Maximum Ratings ..............................................................................166
DC Parameters .................................................................................................166
AC Parameters ................................................................................................. 168
Ordering Information ........................................................................ 178
Packaging Information ..................................................................... 179
PLCC44 ............................................................................................................ 179
VQFP44 ............................................................................................................ 181
Document Revision History ............................................................. 183
Changes from 7663B to 7663C ........................................................................ 183
Changes from 7663C to 7663D ........................................................................ 183
Changes from 7663D to 7663E ........................................................................ 183
3
AT89C51RE2
7663E–8051–10/08
Headquarters
International
Atmel Corporation
2325 Orchard Parkway
San Jose, CA 95131
USA
Tel: 1(408) 441-0311
Fax: 1(408) 487-2600
Atmel Asia
Room 1219
Chinachem Golden Plaza
77 Mody Road Tsimshatsui
East Kowloon
Hong Kong
Tel: (852) 2721-9778
Fax: (852) 2722-1369
Atmel Europe
Le Krebs
8, Rue Jean-Pierre Timbaud
BP 309
78054 Saint-Quentin-enYvelines Cedex
France
Tel: (33) 1-30-60-70-00
Fax: (33) 1-30-60-71-11
Atmel Japan
9F, Tonetsu Shinkawa Bldg.
1-24-8 Shinkawa
Chuo-ku, Tokyo 104-0033
Japan
Tel: (81) 3-3523-3551
Fax: (81) 3-3523-7581
Technical Support
[email protected]
Sales Contact
www.atmel.com/contacts
Product Contact
Web Site
www.atmel.com
Literature Requests
www.atmel.com/literature
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 ATMEL’S TERMS AND CONDITIONS OF SALE LOCATED ON ATMEL’S WEB SITE, 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 OF 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 product 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’s products are not intended, authorized, or warranted for use
as components in applications intended to support or sustain life.
© 2008 Atmel Corporation. All rights reserved. Atmel ®, logo and combinations thereof, and others are registered trademarks or trademarks of
Atmel Corporation or its subsidiaries. Other terms and product names may be trademarks of others.
7663E–8051–10/08