Dallas DS83C320-ECD High-speed microcontroller user guide Datasheet

User’s Guide
….
www.dalsemi.com
High-Speed Microcontroller
User Guide
SmartSocket 16K/64K
SECTION 1: INTRODUCTION
The Dallas Semiconductor High-Speed Microcontroller is an 8051-compatible device that provides
improved performance and power consumption compared to the original version. It retains instruction set
and object code compatibility with the 8051, yet performs the same operations in fewer clock cycles.
Consequently, more throughput is possible for the same crystal speed. As an alternative, the High-Speed
Microcontroller can be run slowly to save power. The more efficient design allows a much slower crystal
speed to get the same results as an original 8051, using much less power.
The fundamental innovation of the High-Speed Microcontroller is the use of only four clocks per
instruction cycle compared with twelve for the original 8051. This results in up to 3 times improvement
in performance. In addition, the High-Speed Microcontroller is updated with several new peripherals and
features while providing all of the standard features of an 80C32. These include 256 bytes of on-chip
RAM, 32 I/O ports, three 16-bit timer/counters, and an on-chip UART. All devices provide 256 bytes of
RAM for variables and stack. 128 bytes can be reached using direct addressing and 128 using indirect
addressing.
In addition to improved efficiency, members of the High-Speed Microcontroller family can operate at a
maximum clock rate of 33 or 40 MHz. Combined with the 3 times performance, this allows for a
maximum performance equivalent to a 99 or 120 MHz 8051. This level of computing power is
comparable to many 16-bit processors, but without the added expense and complexity if implementing a
16-bit interface.
A number of peripherals were added to the original 80C32 core when designing the High-Speed
Microcontroller family. Some devices have a programmable watchdog Timer to supervise the system. It
will count up to a user programmable interval and then reset the CPU unless cleared by software. Other
features such as a second, full-function UART and dual data pointers are available to minimize external
interrupts allows greater flexibility in dealing with external events.
Some members of the High-Speed Microcontroller family incorporate Power Management Modes which
allow the device to dynamically vary the internal clock speed from 4 clocks per cycle (default) to 64 or
1024 clocks per cycle. Because power consumption is directly proportional to clock speed, the device
can reduce its operating frequency during periods of little or no activity. This greatly reduces power
consumption. The switch-back feature allows the device to quickly return in divide by 4 mode upon
receipt of an interrupt or serial port activity, allowing the device to respond to external events while in
Power Management Mode.
Various memory configurations are available with the High-Speed Microcontroller family. EPROM and
Mask programmable ROM versions are available for program memory. Some versions incorporate
extended MOVX SRAM on-chip, reducing or eliminating the need for external data memory. This
memory can be made nonvolatile in the DS87C530 through the use of an external lithium battery.
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SECTION 2: ORDERING INFORMATION
The High-Speed Microcontroller family follows the part numbering convention shown below. Note that
all combinations of devices are not currently available. Please refer to individual data sheets for the
available versions.
DS80C320-MCG
SPEED:
D
G
L
R
18 MHz
25 MHz
33 MHz
40 MHz
TEMPERATURE:
C
N
0°C to 70°C
-40°C to +85°C
PACKAGE:
M
Q
E
F
W
K
PLASTIC
PLCC
THIN PLASTIC QUAD FLAT PACK (TQFP)
PLASTIC QUAD FLAT PACK (QFP)
WINDOWED CERDIP
WINDOWED CERQUAD
OPERATING VOLTAGE:
0
3
+5V
+3V OR WIDE VOLTAGE
MEMORY TYPE:
0
3
7
ROMless
ROM
EPROM
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SECTION 3: ARCHITECTURE
The High-Speed Microcontroller is based on the industry standard 80C52. The core is an accumulator
based architecture using internal registers for data storage and peripheral control. It executes the standard
8051 instruction set. This section provides a brief description of each architecture feature. Details
concerning the programming model, instruction set, and register description are provided in Section 4.
ALU
The ALU is responsible for math functions, comparisons, and general decision making in the High-Speed
Microcontroller. The ALU is not explicitly used by software. Instruction decoding prepares the ALU
automatically and passes it the appropriate data. The ALU primarily uses two special function registers
(SFRs) as the source and destination for all operations. These are the Accumulator and B register. The
ALU also provides status information in the Program Status Register. The SFRs are described below.
SPECIAL FUNCTION REGISTERS
All peripherals and operations that are not explicit instructions in the High-Speed Microcontroller are
controlled via Special Function Registers (SFRs). All SFRs are described in Section 4. The most
commonly used registers that are basic to the architecture are also described below.
Accumulator
The Accumulator is the primary register used in the High-Speed Microcontroller. It is the source and
destination of most math, data movement, decisions, and other operations. Although it can be bypassed,
most high-speed instructions require the use of the Accumulator (ACC) as one argument.
B Register
The B register is used as the second 8-bit argument in multiply and divide operations. When not used for
these purposes, the B register can be used as a general purpose register.
Program Status Word
The Program Status Word holds a selection of bit flags that include the Carry Flag, Auxiliary Carry Flag,
General Purpose Flag, Register Bank Select, Overflow Flag, and Parity Flag.
Data Pointer(s)
The Data Pointer is used to designate a memory address for the MOVX instruction. This address can
point to a MOVX RAM location, either on- or off-chip, or a memory mapped peripheral. When moving
data from one memory area to another or from memory to a memory mapped peripheral, a pointer is
needed for both the source and destination. Thus the High-Speed Microcontroller offers two data
pointers. The user selects the active pointer via a dedicated SFR bit.
Stack Pointer
The microcontroller provides a Stack in the scratchpad RAM area discussed below. The Stack Pointer
denotes the register location at the top of the Stack, which is the last used value. The user can place the
Stack anywhere in scratchpad RAM by setting the Stack Pointer to that location.
I/O Ports
The standard High-Speed Microcontroller offers four 8-bit I/O ports. ROM less versions use Port 0 and
Port 2 as address and data busses. In those versions, only two ports are available for general purpose I/O.
Each I/O port is a Special Function Register that can be written or read. The I/O port has a latch that
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High-Speed Microcontroller User’s Guide
retains the value which software writes. In general, during a read operation, software reads the state of
the external pin. Each port is represented by a SFR location.
Timer/Counters
Three 16-bit Timer/Counters are available in the High-Speed Microcontroller. Each timer is contained in
two SFR locations that can be written or read by software. The timers are controlled by other SFRs
described in Section 4.
UARTs
The High-Speed Microcontroller provides one or two UARTs. These are controlled and accessed as
SFRs. Each UART has an address that is used to read or write the UART. The same address is used for
both read and write operations. The microcontroller distinguishes between a read and a write by the
instruction. Each UART is controlled by its own SFR control register.
SCRATCHPAD REGISTERS (RAM)
The High-Speed Core provides 256 bytes of Scratchpad RAM for general purpose data and variable
storage. The first 128 bytes are directly available to software. The second 128 are available through
indirect addressing discussed below. Selected portions of this RAM have other optional functions.
Stack
The stack is a RAM area that the microcontroller uses to store return address information during Calls
and Interrupts. The user can also place variables on the stack when necessary. The Stack Pointer
mentioned above designates the RAM location that is the top of the stack. Thus, depending on the value
of the Stack Pointer, the stack can be located anywhere in the 256 bytes of RAM. A common location
would be in the upper 128 bytes of RAM, as these are accessible through indirect addressing only.
Working Registers
The first thirty-two bytes of the Scratchpad RAM can be used as four banks of eight Working Registers
for high speed data movement. Using four banks, software can quickly change context by simply
changing to a different bank. In addition to the Accumulator, the Working Registers are commonly used
as data source or destination. Some of the Working Registers can also be used as pointers to other RAM
locations (indirect addressing).
PROGRAM COUNTER
The Program Counter (PC) is a 16-bit value that designates the next program address to be fetched. Onchip hardware automatically increments the PC value to move to the next ROM location.
ADDRESS/DATA BUS
The High-Speed Microcontroller addresses a 64KB program and 64KB data memory area. In the
ROMless versions, all memory is outside. Other versions use a combination of internal and external
memory. When external memory is accessed, Ports 0 and 2 are used as a multiplexed address and data
bus. Port 2 provides the address MSB. Even versions with internal memory can use the bus on Ports 0
and 2 to access more memory.
WATCHDOG TIMER
The Watchdog Timer provides a supervisory function for applications that cannot afford to run out of
control. The Watchdog Timer is a programmable free running timer. If allowed to reach the termination
of its count, if enabled, the Watchdog will reset the CPU. Software must prevent this by cleaning or
resetting the Watchdog prior to its time-out.
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POWER MONITOR
Some members of the High-Speed Microcontroller family incorporate a band-gap reference and analog
circuitry to monitor the power supply conditions. VCC begins to drop out of tolerance, the Power Monitor
will issue an optional early warning Power-fail interrupt. If power continues to fall, the Power Monitor
will invoke a reset condition. This will remain until power returns to normal operating voltage. The
Power Monitor also functions on power-up, holding the microcontroller in a reset state until power is
stable.
INTERRUPTS
The High-Speed Microcontroller is capable of evaluating a number of interrupt sources simultaneously.
Each version of the High-Speed Microcontroller provides a different number of interrupt sources. Each
interrupt has an associated interrupt vector, flag, priority, and enable. These interrupts can be globally
enabled or disabled.
TIMING CONTROL
The High-Speed Microcontroller provides an on-chip oscillator for use with an external crystal. This can
be bypassed by injecting a clock source into the XTAL 1 pin. The clock source is used to create machine
cycle timing (four clocks), ALE, PSEN , Watchdog, Timer, and serial baud rate timing. In addition, some
devices incorporate an on-chip ring oscillator which can be used to provide an approximately 2-4 MHz
clock source.
REAL-TIME CLOCK
The DS87C530 incorporates a real-time clock (RTC), which is accessed via SFR locations. The RTC is
divided into hour, minute, second, and subsecond registers, and also incorporates a 65536 day calendar.
Alarm registers allow the RTC to issue interrupts at a specific time once a day, or as a recurring alarm
every hour, minute or second. An external watch crystal and lithium power source allow the processor to
maintain timekeeping in the absence of VCC.
FEATURE SUMMARY
The High-Speed Microcontroller family offers a combination of features and peripherals as shown in
Table 3-1. This User’s Guide is designed as a comprehensive guide covering all features available in the
High-Speed Microcontroller family. The designer should investigate the specific data sheet to determine
which features are available on a particular device. Detailed information about newer members of the
product family may be provided in separate documents until they can be assimlilated into the High-Speed
Microcontroller User’s Guide.
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PRODUCT FEATURE MATRIX
FEATURE
Table 3-1
DS80C310
DS80C320
DS80C323
Internal Program ROM
Internal Scratchpad RAM
256 bytes
256 bytes
256 bytes
DS83C520
DS87C520
DS87C530
DS87C550
16KB
Mask ROM
16KB
EPROM
16KB
EPROM
8KB
EPROM
256 bytes
256 bytes
256 bytes
256 bytes
1KB SRAM
1KB SRAM
Internal MOVX SRAM
Serial Ports
1
2
2
2
2
2
2
External Interrupts
6
6
6
6
6
6
6
16-bit Timers
3
3
3
3
3
3
3
Watchdog Timer
√
√
√
√
√
√
Power-fail/Precision Reset
√
√
√
√
√
√
Power-fail Interrupt
√
√
√
√
√
√
2
2
2
2
2
2
Data Pointers
2
√
Data Pointer Decrement
Power Management Modes
√
Ring Oscillator
√
EMI Reduction Mode
√
√
√
√
√
√
√
√
√
√
√
√
Real-Time Clock
√
Nonvolatile SRAM
√
4
Pulse Width Modulation
8-bit
or
2
8 Channels
10-bit
A/D Converter
Operating Voltage
16-bit
4.5V-5.5V
4.5V-5.5V
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2.7V-5.5V
4.5V-5.5V
4.5V-5.5V
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4.5V-5.5V
4.5V-5.5V
SECTION 4: PROGRAMMING MODEL
This section provides a programmer’s overview of the High-Speed Microcontroller core. It includes
information on the memory map, on-chip RAM, Special Function Registers (SFRs), and instruction set.
The programming model of the High-Speed Microcontroller is very similar to that of the industry
standard 80C52. The memory map is identical. It uses the same instruction set, though instruction timing
is improved. Several new SFRs have been added.
MEMORY ORGANIZATION
The High-Speed Microcontroller, like the 8052, uses several distant memory areas. These are Registers,
program memory, and data memory. Registers serve to control on-chip peripherals and as RAM. Note
that registers (on-chip RAM) are separate from data memory. Registers are divided into three categories
including directly addressed on-chip RAM, indirectly addressed on-chip RAM, and Special Function
Registers. The program and data memory areas are discussed under Memory Map. The Registers are
discussed under Registers Map.
MEMORY MAP
The High-Speed Microcontroller uses a memory addressing scheme that separates program memory
(ROM) from data memory (RAM). Each area is 64KB beginning at address 0000h and ending at FFFFh
as shown in Figure 4-1. The program and data segments can overlap since they are accessed in different
ways. Program memory is fetched by the microcontroller automatically. These addresses are never
written by software. In fact, there are no instructions that allow the ROM area to be written. There is one
instruction (MOVC) that is used to explicitly read the program area. This is commonly used to read lookup tables. The data memory area is accessed explicitly using the MOVX instruction. This instruction
provides multiple ways of specifying the target address. It is used to access the 64KB of data memory.
The address and data range of devices with on-chip program and data memory overlap the 64K memory
space. When on-chip memory is enabled, accessing memory in the on-chip range will cause the device to
access internal memory. Memory accesses beyond the internal range will be addressed externally via
ports 0 and 2.
The ROMSIZE feature allows software to dynamically configure the maximum address of on-chip
program memory. This allows the device to act as a bootstrap loader for an external Flash or Nonvolatile
SRAM. Secondly, this method can also be used to increase the amount of available program memory
from 64KB to 80KB without bank switching. For more information on this feature, please consult
Section 6.
Program and data memory can also be increased beyond the 64KB limit using bank switching techniques.
This is described in Application Note 81, Memory Expansion with the High-Speed Microcontroller
family.
REGISTER MAP
The Register Map is illustrated in Figure 4-2. It is entirely separate from the program and data memory
areas mentioned above. A separate class of instructions is used to access the registers. There are 256
potential register location values. In practice, the High-Speed Microcontroller has 256 bytes of
Scratchpad RAM and up to 128 Special Function Registers (SFRs). This is possible since the upper 128
Scratchpad RAM locations can only be accessed indirectly. That is, the contents of a Working Register
(described below) will designate the RAM location. Thus a direct reference to one of the upper 128
locations must be an SFR access. Direct RAM is reached at locations 0 to 7Fh (0 to 127).
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SFRs are accessed directly between 80h and FFh (128 to 255). The RAM locations between 128 and 255
can be reached through an indirect reference to those locations.
Scratchpad RAM is available for general purpose data storage. It is commonly used in place of off-chip
RAM when the total data contents are small. When off-chip RAM is needed, the Scratchpad area will
still provide the fastest general purpose access. Within the 256 bytes of RAM, there are several special
purpose areas. These are described as follows:
Bit Addressable Locations
In addition to direct register access, some individual bits are also accessible. These are individually
addressable bits in both the RAM and SFR area. In the Scratchpad RAM area, registers 20h to 2Fh are bit
addressable. This provides 126 (16 * 8) individual bits available to software. A bit access is
distinguished from a full register access by the type of instruction. Addressing modes are discussed in
Section 5. In the SFR area, any register location ending in a 0 or 8 is bit addressable. Figure 4-3 shows
details of the on-chip RAM addressing including the locations of individual RAM bits.
Working Registers
As part of the lower 128 bytes of RAM, there are four banks of Working Registers (each). The Working
registers are general purpose RAM locations that can be addressed in a special way. They are designated
R0 through R7. Since there are four banks, the currently selected bank will be used by any instruction
using R0-R7. This allows software to change context by simply switching banks. This is controlled via
the Program Status Word register in the SFR area described below. The Working Registers also allow
their contents to be used for indirect addressing of the upper 128 bytes of RAM. Thus an instruction can
designate the value stored in R0 (for example) to address the upper RAM. This value might be the result
of another calculation.
Stack
Another use of the Scratchpad area is for the programmer’s stack. This area is selected using the Stack
Pointer (SP;81h) SFR. Whenever a call or interrupt is invoked, the return address is placed on the Stack.
It also is available to the programmer for variables, etc. since the Stack can be moved, there is no fixed
location within the RAM designated as Stack. The Stack Pointer will default to 07h on reset. The user
can then move it as needed. A convenient location would be the upper RAM area (>7Fh) since this is
only available indirectly. The SP will point to the last used value. Therefore, the next value placed on
the Stack is put at SP + 1. Each PUSH or CALL will increment the SP by the appropriate value. Each
POP or RET will decrement as well.
MEMORY MAP Figure 4-1
FFFFh
64K
PROGRAM
MEMORY
DATA
MEMORY
0000h
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High-Speed Microcontroller User’s Guide
REGISTER MAP Figure 4-2
FFh
255
INDIRECT
RAM
128
7Fh
DIRECT
SPECIAL
FUNCTION
REGISTERS
DIRECT
RAM
0000h
SCRATCHPAD REGISTER ADDRESSING Figure 4-3
FFh
INDIRECT RAM
7Fh
DIRECT RAM
2Fh
2Eh
2Dh
2Ch
2Bh
2Ah
29h
28h
27h
26h
25h
24h
23h
22h
21h
20h
1Fh
7F
77
6F
67
5F
57
4F
47
3F
37
2F
27
1F
17
0F
07
7E
76
6E
66
5E
56
4E
46
3E
36
2E
26
1E
16
0E
06
7D
75
6D
65
5D
55
4D
45
3D
35
2D
25
1D
15
0D
05
7C
74
6C
64
5C
54
4C
44
3C
34
2C
24
1C
14
0C
04
7B
73
6B
63
5B
53
4B
43
3B
333
2B
23
1B
13
0B
03
7A
72
6A
62
5A
52
4A
42
3A
32
2A
22
1A
12
0A
02
79
71
69
61
59
51
49
41
39
31
29
21
19
11
09
01
78
70
68
60
58
50
48
40
38
30
28
20
18
10
08
00
BANK 3
18h
17h
BANK 2
10h
0Fh
BANK 1
08h
07h
BANK 0
00h
MSB
LSB
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FFh
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High-Speed Microcontroller User’s Guide
SPECIAL FUNCTION REGISTERS
The High-Speed Microcontroller, like the 8051, uses Special Function Registers (SFRs) to control
peripherals and modes. In many cases, an SFR will control individual functions or report status on
individual functions. The SFRs reside in register locations 80h-FFh and are reached using direct
addressing. SFRs that end in 0 or 8 are bit addressable.
All standard SFR locations from the original 8051 are duplicated in the High-Speed Microcontroller, with
several additions. Following tables illustrate the locations of the SFRs for various devices. Following
each tables a description of the default reset conditions of all SFR bits. The following section is a
detailed description of each Special Function Register.
DS80C310 SPECIAL FUNCTION REGISTER LOCATIONS Table 4-1
REGISTER
SP
DPL
DPH
DPL1
DPH1
DPS
PCON
TCON
TMOD
TL0
TL1
TH0
TH1
CKCON
P1
EXIF
SCON0
SBUF0
P2
IE
SADDR0
P3
IP
SADEN0
STATUS
T2CON
T2MOD
RCAP2L
RCAP2H
TL2
TH2
PSW
WDCON
ACC
EIE
B
EIP
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
SMOD-0
TF1
GATE
0
SMOD0
TR1
0
TF0
M1
0
TR0
M0
0
GF1
IE1
GATE
0
GF0
IT1
0
STOP
IE0
M1
SEL
IDLE
IT0
M0
C/ T
C/ T
P1.7
IE5
SM0/FE_0
P1.6
IE4
SM1_0
T2M
P1.5
IE3
SM2_0
T1M
P1.4
IE2
REN_0
T0M
P1.3
TB8_0
MD2
P1.2
RB8_0
MD1
P1.1
TI_0
MD0
P1.0
RI_0
P2.7
EA
P2.6
-
P2.5
ET2
P2.4
ES0
P2.3
ET1
P2.2
EX1
P2.1
ET0
P2.0
EX0
P3.7
-
P3.6
-
P3.5
PT2
P3.4
PS0
P3.3
PT1
P3.2
PX1
P3.1
PT0
P3.0
PX0
0
TF2
HIP
EXF2
LIP
RCLK
1
TCLK
1
EXEN2
1
TR2
1
1
-
-
-
-
-
-
C/ T2
T2OE
CP/ RL2
DCEN
CY
-
AC
POR
F0
-
RS1
-
RS0
-
OV
-
F1
-
P
-
-
-
-
-
EX5
EX4
EX3
EX2
-
-
-
-
PX5
PX4
PX3
PX2
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ADDRESS
81h
82h
83h
84h
85h
86h
87h
88h
89h
8Ah
8Bh
8Ch
8Dh
8Eh
90h
91h
98h
99h
A0h
A8h
A9h
B0h
B8h
B9h
C5h
C8h
C9h
CAh
CBh
CCh
CDh
D0h
D8h
E0h
E8h
F0h
F8h
High-Speed Microcontroller User’s Guide
S80C310 SPECIAL FUNCTION REGISTER RESET VALUES Tables 4-2
REGISTER
SP
DPL
DPH
DPL1
DPH1
DPS
PCON
TCON
TMOD
TL0
TL1
TH0
TH1
CKCON
P1
EXIF
SCON0
SBUF0
P2
IE
SADDR0
P3
IP
SADEN0
STATUS
T2CON
T2MOD
RCAP2L
RCAP2H
TL2
TH2
PSW
WDCON
ACC
EIE
B
EIP
BIT 7
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
1
0
0
0
0
0
0
0
0
0
0
-
BIT 6
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
1
0
0
0
0
0
0
0
0
SPECIAL
0
0
-
BIT 5
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
-
BIT 4
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
1
0
0
1
0
0
0
0
0
0
0
0
-
BIT 3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
1
0
0
1
0
0
1
0
0
0
0
0
0
0
0
0
0
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BIT 2
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
1
0
0
1
0
0
1
0
0
0
0
0
0
0
0
0
0
BIT 1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
1
0
0
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
BIT 0
1
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
0
1
0
0
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
ADDRESS
81h
82h
83h
84h
85h
86h
87h
88h
89h
8Ah
8Bh
8Ch
8Dh
8Eh
90h
91h
98h
99h
A0h
A8h
A9h
B0h
B8h
B9h
C5h
C8h
C9h
CAh
CBh
CCh
CDh
D0h
D8h
E0h
E8h
F0h
F8h
High-Speed Microcontroller User’s Guide
DS80C320/DS80C323 SPECIAL FUNCTION REGISTER LOCATIONS
Table 4-3
REGISTER
SP
DPL
DPH
DPL1
DPH1
DPS
PCON
TCON
TMOD
TL0
TL1
TH0
TH1
CKCON
P1
EXIF
SCON0
SBUF0
P2
IE
SADDR0
SADDR1
P3
IP
SADEN0
SADEN1
SCON1
SBUF1
STATUS
TA
T2CON
T2MOD
RCAP2L
RCAP2H
TL2
TH2
PSW
WDCON
ACC
EIE
B
EIP
BIT 7
0
SMOD_0
TF1
GATE
BIT 6
0
SMOD0
TR1
C/ T
BIT 5
0
TF0
M1
BIT 4
0
TR0
M0
BIT 3
0
GF1
IE1
GATE
BIT 2
0
GF0
IT1
C/ T
BIT 1
0
STOP
IE0
M1
BIT 0
SEL
IDLE
IT0
M0
WD1
P1.7
IE5
SM0/FE_0
WD0
P1.6
IE4
SM1_0
T2M
P1.5
IE3
SM2_0
T1M
P1.4
IE2
REN_0
T0M
P1.3
TB8_0
MD2
P1.2
RGMD
RB8_0
MD1
P1.1
RGSL
TI_0
MD0
P1.0
BGS
RI_0
P2.7
EA
P2.6
ES1
P2.5
ET2
P2.4
ES0
P2.3
ET1
P2.2
EX1
P2.1
ET0
P2.0
EX0
P3.7
-
P3.6
PS1
P3.5
PT2
P3.4
PS0
P3.3
PT1
P3.2
PX1
P3.1
PT-
P3.0
PX0
SMO/FE_1
SM1_1
SM2_1
REN_1
TB8_1
RB8_1
I1_1
R1_1
PIP
HIP
LIP
1
1
1
1
1
TF2
EXF2
RCLK
TCLK
EXEN2
TR2
-
-
-
-
-
-
C/T2
T2OE
CP/RL2
DCEN
CY
SMOD_1
AC
POR
F0
EPF1
RS1
PF1
RS0
WDIF
OV
WTRF
F1
EWT
P
RWT
-
-
-
EWDI
EX5
EX4
EX3
EX2
-
-
-
PWDI
PX5
PX4
PX3
PX2
Shaded bits are Timed Access protected
12 of 175
ADDRESS
81h
82h
83h
84h
85h
86h
87h
88h
89h
8Ah
8Bh
8Ch
8Dh
8Eh
90h
91h
98h
99h
A0h
A8h
A9h
AAh
B0h
B8h
B9h
Bah
C0h
C1h
C5h
C7h
C8h
C9h
CAh
CBh
CCh
CDh
D0h
D8h
E0h
E8h
F0h
F8h
High-Speed Microcontroller User’s Guide
DS80C320/DS80C323 SPECIAL FUNCTION REGISTER RESET VALUES
Table 4-4
REGISTER
SP
DPL
DPH
DPL1
DPH1
DPS
PCON
TCON
TMOD
TL0
TL1
TH0
TH1
CKCON
P1
EXIF
SCON0
SBUF0
P2
IE
SADDR0
SADDR1
P3
IP
SADEN0
SADEN1
SCON1
SBUF1
STATUS
TA
T2CON
T2MOD
RCAP2L
RCAP2H
TL2
TH2
PSW
WDCON
ACC
EIE
B
EIP
BIT 7
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
1
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
BIT 6
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
SPECIAL
0
0
BIT 5
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
BIT 4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
1
1
0
0
0
0
0
0
SPECIAL
0
0
BIT 3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
1
1
0
0
0
0
0
0
0
0
0
0
BIT 2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
1
1
0
0
0
0
0
0
SPECIAL
0
0
0
BIT 1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
1
1
0
0
0
0
0
0
0
SPECIAL
0
0
0
BIT 0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
1
1
0
0
0
0
0
0
0
0
0
0
0
ADDRESS
81h
82h
83h
84h
85h
86h
87h
88h
89h
8Ah
8Bh
8Ch
8Dh
8Eh
90h
91h
98h
99h
A0h
A8h
A9h
AAh
B0h
B8h
B9h
BAh
C0h
C1h
C5h
C7h
C8h
C9h
CAh
CBh
CCh
CDh
D0h
D8h
E0h
E8h
F0h
--
-
-
0
0
0
0
0
F8h
13 of 175
High-Speed Microcontroller User’s Guide
DS83C520/DS87C520 SPECIAL FUNCTION REGISTER LOCATIONS
Table 4-5
REGISTER
P0
SP
DPL
DPH
DPL1
DPH1
DPS
PCON
TCON
TMOD
BIT 7
P0.7
BIT 6
P0.6
BIT 5
P0.5
BIT 4
P0.4
BIT 3
P0.3
BIT 2
P0.2
BIT 1
P0.1
BIT 0
P0.0
0
SMOD_0
TF1
GATE
0
SMOD0
TR1
0
TF0
M1
0
TR0
M0
0
GF1
IE1
GATE
0
GF0
IT1
0
STOP
IE0
M1
SEL
IDLE
IT0
M0
ADDRESS
80h
81h
82h
83h
84h
85h
86h
87h
88h
89h
8Ah
8Bh
8Ch
8Dh
8Eh
C/ T
C/ T
TL0
TL1
TH0
TH1
CKCON
WD1
WD0
T2M
T1M
T0M
MD2
MD1
MD0
P1
P1.7
P1.6
P1.5
P1.4
P1.3
P1.2
P1.1
P1.0
RGMD
RB8_0
RGSL
TI_0
BGS
RI_0
EXIF
SCON0
SBUF0
P2
IE
SADDR0
SADDR1
P3
IP
SADEN0
SADEN1
SCON1
SBUF1
ROMSIZE
PMR
STATUS
TA
T2CON
T2MOD
RCAP2L
RCAP2H
TL2
TH2
PSW
WDCON
ACC
EIE
B
EIP
IE5
SM0/FE_0
IE4
SM1_0
IE3
SM2_0
IE2
REN_0
XT/ RG
TB8_0
P2.7
EA
P2.6
ES1
P2.5
ET2
P2.4
ES0
P2.3
ET1
P2.2
EX1
P2.1
ET0
P2.0
EX0
P3.7
-
P3.6
PS1
P3.5
PT2
P3.4
PS0
P3.3
PT1
P3.2
PX1
P3.1
PT0
P3.0
PX0
SM0/FE_1
SM1_1
SM2_1
REN_1
TB8_1
RB8_1
TI_1
RI_1
CD1
PIP
CD0
HIP
SWB
LIP
XTUP
XTOFF
SPTA1
RMS2
ALEOFF
SPRA1
RMS1
DME1
SPTA0
RMS0
DME0
SPRA0
TF2
-
EXF2
-
RCLK
-
TCLK
-
EXEN2
-
TR2
-
C/ T2
T2OE
CP/ RL2
DCEN
CY
SMOD_1
AC
POR
F0
EPFI
RS1
PFI
RS0
WDIF
OV
WTRF
F1
EWT
P
RWT
-
-
-
EWDI
EX5
EX4
EX3
EX2
-
-
-
PWD1
PX5
PX4
PX3
PX2
Shaded bits are Timed Access protected
14 of 175
90h
91h
98h
99h
A0h
A8h
A9h
AAh
B0h
B8h
B9h
BAh
C0h
C1h
C2h
C4h
C5h
C7h
C8h
C9h
CAh
CBh
CCh
CDh
D0h
D8h
E0h
E8h
F0h
F8h
High-Speed Microcontroller User’s Guide
DS83C520/DS87C520 SPECIAL FUNCTION REGISTER RESET VALUES
Table 4-6
REGISTER
P0
SP
DPL
DPH
DPL1
DPH1
DPS
PCON
TCON
TMOD
TL0
TL1
TH0
TH1
CKCON
P1
EXIF
SCON0
SBUF0
P2
IE
SADDR0
SADDR1
P3
IP
SADEN0
SADEN1
SCON1
SBUF1
ROMSIZE
PMR
STATUS
TA
T2CON
T2MOD
RCAP2L
RCAP2H
TL2
TH2
PSW
WDCON
ACC
EIE
B
EIP
BIT 7
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
-
BIT 6
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
1
0
0
0
0
0
1
0
1
0
0
0
0
0
0
SPECIAL
0
0
-
BIT 5
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
1
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
-
BIT 4
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
1
0
0
0
0
0
SPECIAL
1
0
0
0
0
0
0
SPECIAL
0
0
0
0
BIT 3
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
SPECIAL
0
0
1
0
0
0
1
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
15 of 175
BIT 2
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
SPECIAL
0
0
1
0
0
0
1
0
0
0
0
0
1
0
0
1
0
0
0
0
0
0
SPECIAL
0
0
0
0
BIT 1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
SPECIAL
0
0
1
0
0
0
1
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
SPECIAL
0
0
0
0
BIT 0
1
1
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
0
0
1
0
0
0
1
0
0
0
0
0
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
ADDRESS
80h
81h
82h
83h
84h
85h
86h
87h
88h
89h
8Ah
8Bh
8Ch
8Dh
8Eh
90h
91h
98h
99h
A0h
A8h
A9h
AAh
B0h
B8h
B9h
BAh
C0h
C1h
C2h
C4h
C5h
C7h
C8h
C9h
CAh
CBh
CCh
CDh
D0h
D8h
E0h
E8h
F0h
F8h
High-Speed Microcontroller User’s Guide
DS87C530 SPECIAL FUNCTION REGISTER LOCATION Tables 4-7
REGISTER
P0
SP
DPL
DPH
DPL1
DPH1
DPS
PCON
TCON
TMOD
BIT 7
P0.7
BIT 6
P0.6
BIT 5
P0.5
BIT 4
P0.4
BIT 3
P0.3
BIT 2
P0.2
BIT 1
P0.1
BIT 0
P0.0
0
SMOD_0
TF1
GATE
0
SMOD0
TR1
0
TF0
M1
0
TR0
M0
0
GF1
IE1
GATE
0
GF0
IT1
0
STOP
IE0
M1
SEL
IDLE
IT0
M0
C/ T
C/ T
TL0
TL1
TH0
TH1
CKCON
P1
WD1
P1.7
WD0
P1.6
T2M
P1.5
T1M
P1.4
T0M
P1.3
MD2
P1.2
MD1
P1.1
MD0
P1.0
EXIF
IE5
IE4
IE3
IE2
XT/ RG
RGMD
RGSL
BGS
TRIM
SCON0
SBUF0
P2
IE
SADDR0
SADDR1
P3
IP
SADEN0
SADEN1
SCON1
SBUF1
ROMSIZE
PMR
STATUS
TA
T2CON
T2MOD
RCAP2L
RCAP2H
TL2
TH2
PSW
WDCON
ACC
EIE
B
RTASS
RTAS
RTAM
RTAH
E4K
SM0/FE_0
X12/ 6
SM1_0
TRM2
SM2_0
TRM2
REN_0
TRM1
TB8_0
TRM1
RB8_0
TRM0
TI_0
TRM0
RI_0
P2.7
EA
P2.6
ES1
P2.5
ET2
P2.4
ES0
P2.3
ET1
P2.2
EX1
P2.1
ET0
P2.0
EX0
P3.7
-
P3.6
PS1
P3.5
PT2
P3.4
PS0
P3.3
PT1
P3.2
PX1
P3.1
PT0
P3.0
PX0
SM0/FE_1
SM1_1
SM2_1
REN_1
TB8_1
RB8_1
TI_1
RI_1
CD1
PIP
CD0
HIP
SWB
LIP
XTUP
XTOFF
SPTA1
RMS2
ALEOFF
SPRA1
RMS1
DME1
SPTA0
RMS0
DME0
SPRA0
TF2
-
EXF2
-
RCLK
-
TCLK
-
EXEN2
-
TR2
-
C/ T2
T2OE
CP/ RL2
DCEN
CY
SMOD_0
AC
POR
F0
EPFI
RS1
PFI
RS0
WDIF
OV
WTRF
F1
EWT
P
RWT
-
-
ERTCI
EWDI
EX5
EX4
EX3
EX2
0
0
0
0
0
0
0
16 of 175
ADDRESS
80h
81h
82h
83h
84h
85h
86h
87h
88h
89h
8Ah
8Bh
8Ch
8Dh
8Eh
90h
91h
96h
98h
99h
A0h
A8h
A9h
AAh
B0h
B8h
B9h
BAh
C0h
C1h
C2h
C4h
C5h
C7h
C8h
C9h
CAh
CBh
CCh
CDh
D0h
D8h
E0h
E8h
F0h
F2h
F3h
F4h
F5h
High-Speed Microcontroller User’s Guide
DS87C530 SPECIAL FUNCTION REGISTER LOCATION Tables 4-7( Cont.)
REGISTER
EIP
RTCC
RTCSS
RTCS
RTCM
RTCH
RTCD0
RTCD1
BIT 7
SSCE
BIT 6
SCE
0
0
0
0
BIT 5
PRTCI
MCE
BIT 4
PWDI
HCE
BIT 3
PX5
RTCE
Shaded bits are Timed Access protected
17 of 175
BIT 2
PX4
RTCWE
BIT 1
PX3
RTCIF
BIT 0
PX2
RTCE
ADDRESS
F8h
F9h
FAh
FBh
FCh
FDh
FEh
FFh
High-Speed Microcontroller User’s Guide
DS87C530 SPECIAL FUNCTION REGISTER RESET VALUES Tables 4-8
REGISTER
PO
SP
DPL
DPH
DPL1
DPH1
DPS
PCON
TCON
TMOD
TL0
TL1
TH0
TH1
CKCON
P1
BIT 7
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
BIT 6
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
BIT 5
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
BIT 4
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
BIT 3
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
BIT 2
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
BIT 1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
BIT 0
1
1
0
0
0
0
0
0
0
0
0
0
0
0
1
1
ADDRESS
80h
81h
82h
83h
84h
85h
86h
87h
88h
89h
8Ah
8Bh
8Ch
8Dh
8Eh
90h
0
SPECIAL
0
SPECIAL
0
SPECIAL
0
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
0
SPECIAL
91h
96h
0
0
1
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
1
0
1
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
-
0
0
1
0
0
0
1
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
1
0
0
1
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
1
0
0
1
0
0
0
0
0
0
0
98h
99h
A0h
A8h
A9h
AAh
B0h
B8h
B9h
BAh
C0h
C1h
C2h
C4h
C5h
C7h
C8h
C9h
CAh
CBh
CCh
CDh
D0h
WDCON
0
SPECIAL
0
SPECIAL
0
SPECIAL
SPECIAL
0
D8h
ACC
EIE
B
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
E0h
E8h
F0h
RTASS
RTAS
RTAM
RTAH
SPECIAL
0
0
0
SPECIAL
0
0
0
SPECIAL
SPECIAL
SPECIAL
0
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
F2h
F3h
F4h
F5h
EXIF
TRIM
SCON0
SBUF0
P2
IE
SADDR0
SADDR1
P3
IP
SADEN0
SADEN1
SCON1
SBUF1
ROMSIZE
PMR
STATUS
TA
T2CON
T2MOD
RCAP2L
RCAP2H
TL2
TH2
PSW
EIP
RTCC
RTCSS
RTCS
RTCM
RTCH
RTCD0
SPECIAL
1
0
0
0
0
0
0
-
-
0
0
0
0
0
0
F8h
SPECIAL
SPECIAL
0
0
SPECIAL
SPECIAL
SPECIAL
SPECIAL
0
0
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
0
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
0
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
F9h
FAh
FBh
FCh
FDh
FEh
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High-Speed Microcontroller User’s Guide
RTCD1
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
SPECIAL
FFh
SPECIAL FUNCTION REGISTERS
Most of the unique features of the High-Speed Microcontroller family are controlled by bits in special
function registers (SFRs) located in unused locations in the 8051 SFR map. This allows for increased
functionality while maintaining complete instruction set compatibility.
The description for each bit indicates its read and write access, as well as its state after a power on reset.
Bits which are affected by a no-battery reset are also indicated. Note that many bits and registers are
unique to specific devices, and their functions will vary between different members of the High-Speed
Microcontroller family.
Port 0 (P0)
SFR 80h
7
6
5
4
3
2
1
0
P0.7
P0.6
P0.5
P0.4
P0.3
P0.2
P0.1
P0.0
RW-1
RW-1
RW-1
RW-1
RW-1
RW-1
RW-1
RW-1
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Port 0. This port functions as a multiplexed address/data bus during external
memory access, and as a general purpose I/O port on devices which incorporate
internal program memory. During external memory cycles, this port will contain
the LSB of the address when ALE is high, and data when ALE is low.
P0.7-0
Stack Pointer (SP)
SFR 81h
7
6
5
4
3
2
1
0
SP.7
SP.6
SP.5
SP.4
SP.3
SP.2
SP.1
SP.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-1
RW-1
RW-1
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Stack Pointer. This stack pointer identifies the location where the stack will
begin. The stack pointer is incremented before every PUSH operation. This
register defaults to 07h after reset.
SP.7-0
Bits 7-0
Data Pointer Low 0 (DPL)
SFR 82h
7
6
5
4
3
PDL.7
PDL.6
PDL.5
PDL.4
PDL.3
RW-0
RW-0
RW-0
RW-0
RW-0
2
PDL.2
RW-0
1
0
PDL.1
PDL.0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
DPL.7-0
Bits 7-0
Data Pointer Low 0. This register is the low byte of the standard 80C32 16-bit
data pointer. DPL and DPH are used to point to non-scratchpad data RAM.
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High-Speed Microcontroller User’s Guide
Data Pointer High 0 (DPH)
SFR 83h
7
6
5
4
3
DPH.7
DPH.6
DPH.5
DPH.4
DPH.3
RW-0
RW-0
RW-0
RW-0
RW-0
2
DPH.2
RW-0
1
0
DPH.1
DPH.0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Data Pointer High 0. This register is the high byte of the standard 80C32 16-bit
data pointer. DPL and DPH are used to point to non-scratchpad data RAM.
DPH.7-0
Bits 7-0
Data Pointer Low 1 (DPL1)
SFR 84h
7
6
5
4
3
DPL1.7
DPL1.6
DPL1.5
DPL1.4
DPL1.3
RW-0
RW-0
RW-0
RW-0
RW-0
2
DPL1.2
RW-0
1
0
DPL1.1
DL1H.0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Data Pointer Low 1. This register is the low byte of the auxiliary 16-bit data
pointer. When the SEL bit (DPS.0) is set, DPL1 and DPH1 are used in place of
DPL and DPH during DPTR operations.
DPL1.7-0
Bits 7-0
Data Pointer High 1 (DPH1)
Data
Pointer
High 1
(DPH1)
7
6
5
4
3
SFR 85h
DPH1.7
DPH1.6
DPH1.5
DPH1.4
DPH1.3
RW-0
RW-0
RW-0
RW-0
RW-0
2
DPH1.2
RW-0
1
0
DPH1.1
DPH1.0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Data Pointer High 1. This register is the high byte of the auxiliary 16-bit data
pointer. When the SEL bit (DPS.0) is set, DPL1 and DPH1 are used in place of
DPL and DPH during DPTR operations.
DPH1.7-0
Bits 7-0
Data Pointer Select (DPS)
SFR 86h
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
SEL
R-0
R-0
R-0
R-0
R-0
R-0
R-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Bits 7-0
Reserved. These bits will read 0.
SEL
Bit 0
Data Pointer Select. This bit selects the active data pointer.
0 = Instructions that use the DPTR will use PDL and PDH.
1= Instructions that use the DPTR will use PDL1 and PDH1.
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Power Control (PCON)
SFR 87h
7
6
5
4
3
2
1
0
SMOD_0
SMOD0
-
-
GF1
GF0
STOP
IDLE
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
SMOD_0
Bit 7
Serial Port 0 Baud Rate Doubler Enable. This bit enables/disables the
serial baud rate doubling function for Serial Port 0.
0 = Serial Port 0 baud rate will be that defined by baud rate generation
equation.
1 = Serial Port 0 baud rate will be double that defined by baud rate generation
equation.
GF1
Bit 3
Framing Error Detection Enable. This bit selects function of the
SCON0.7 and SCON1.7 bits.
0 = SCON0.7 and SCON1.7 control the SM0 function defined for the
SCON0 and SCON1 registers.
1 = SCON0.7 and SCON1.7 are converted to the Framing Error (FE) flag for the
respective Serial Port.
Reserved. Read data is indeterminate.
General Purpose User Flag 1. This is a general purpose flag for software
control.
GF0
Bit 2
General Purpose User Flag 0. This is a general purpose flag for software
control.
STOP
Bit 1
Stop Mode Select. Setting this bit will stop program execution, halt the CPU
oscillator, and internal timers, and place the CPU in a low-power mode. This bit
will always be read as a 0. Setting this bit while the Idle bit is set will place the
device in an undefined state.
Idle Mode Select. Setting this bit will stop program execution but leave the
CPU oscillator, timers, serial ports, and interrupts active. This bit will always be
read as a 0.
SMOD0
Bit 6
Bits 5-4
IDLE
Bit 0
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High-Speed Microcontroller User’s Guide
Timer/Counter Control (TCON)
SFR 88h
7
6
5
4
3
2
1
0
TF1
TR1
TF0
TR0
IE1
IT1
IE0
IT0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
TF1
Bit 7
TR1
Bit 6
TF0
Bit 5
TR0
Bit 4
IE1
Bit 3
IT1
Bit 2
Timer 1 Overflow Flag. This bit indicates when Timer 1 overflows its
maximum count as defined by the current mode. This bit can be cleared by
software and is automatically cleared when the CPU vectors to the Timer
1 interrupt service routine.
0 = No Timer 1 overflow has been detected.
1 = Timer 1 has overflowed its maximum count.
Timer 1 Run Control. This bit enables/disables the operation of Timer 1.
0 = Timer 1 is halted.
1 = Timer 1 is enabled.
Timer 0 Overflow Flag. This bit indicates when Timer 0 overflows its
maximum count as defined by the current mode. This bit can be cleared by
software and is automatically cleared when the CPU vectors to the Timer 0
interrupt service routine or by software.
0 = No Timer 0 overflow has been detected.
1 = Timer 0 has overflowed its maximum count.
Timer 0 Run Control. This bit enables/disables the operation of Timer 0.
0 = Timer 0 is halted.
1 = Timer 0 is enabled.
Interrupt 1 Edge Detect. This bit is set when an edge/level of the type defined
by IT1 is detected. If IT1=1, this bit will remain set until cleared in software or
the start of the External Interrupt 1 service routine. If IT1=0, this bit will
inversely reflect the state of the INT1 pin.
Interrupt 1 Type Select. This bit selects whether the INT1 pin will detect edge
or level triggered interrupts.
0 = INT1 is level triggered.
IE0
Bit 1
1 = INT1 is edge triggered.
Interrupt 0 Edge Detect. This bit is set when an edge/level of the type defined
by IT0 is detected. If IT0=1, this bit will remain set until cleared in software or
the start of the External Interrupt 0 service routine. If IT0=0, this bit will
inversely reflect the state of the INT0 pin
IT0
Bit 0
Interrupt 0 Type Select. This bit selects whether the INT0 pin will detect edge
or level triggered interrupts.
0 = INT0 is level triggered.
1 = INT0 is edge triggered.
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High-Speed Microcontroller User’s Guide
Timer Mode Control (TMOD)
SFR 89h
7
6
5
4
3
2
1
0
GATE
C/ T
M1
M0
GATE
C/ T
M1
M0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
GATE
Bit 7
Timer 1 Gate Control. This bit enable/disables the ability of Timer 1 to
increment.
0 = Timer 1 will clock when TR1=1, regardless of the state of INT .
1 = Timer 1 will clock only when TR1=1 and INT1 =1.
C/T
Bit 6
M1, M0
Bits 5-4
Timer 1 Counter/Timer Select.
0 = Timer 1 is incremented by internal clocks.
1 = Timer 1 is incremented by pulses on T1 when TR1 (TCON.6) is 1.
Timer 1 Mode Select. These bits select the operating mode of Timer 1.
M1 M0
Mode
0
0
Mode 0: 8 bits with 5-bit prescale
0
1
Mode 1: 16 bits
1
0
Mode 2: 8 bits with auto-reload
1
1
Mode 3: Timer 1 is halted, but holds its
count
GATE
Bit 3
Timer 0 Gate Control. This bit enables/disables that ability of Timer 0 to
increment.
0 = Timer 0 will clock when TR0=1, regardless of the state of INT0 .
1 = Timer 0 will clock only when TR0=1 and INT0 =1.
C/ T
Bit 2
M1, M0
Bits 1-0
Timer 0 Counter/Timer Select.
0 = Timer incremented by internal clocks.
1 = Timer 1 is incremented by pulses on T0 when TR0 (TCON.4) is 1.
Timer 0 Mode Select. These bits select the operating mode of Timer 0.
When Timer 0 is in mode 3, TL0 is started/stopped by TR0 and TH0 is
started/stopped by TR1. Run control from Timer 1 is then provided via the
Timer 1 mode selection.
M1
0
0
1
1
M0
0
1
0
1
Mode
Mode 0: 8 bits with 5-bit prescale
Mode 1: 16 bits
Mode 2: 8 bits with auto-reload
Mode 3: Timer 0 is two 8 bit counters.
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High-Speed Microcontroller User’s Guide
Timer 0 LSB (TL0)
SFR 8Ah
7
6
5
4
3
2
1
0
TL0.7
TL0.6
TL0.5
TL0.4
TL0.3
TL0.2
TL0.1
TL0.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Timer 0 LSB. This register contains the least significant byte of Timer 0.
TL0.7-0
Bits 7-0
Timer 1 LSB (TL1)
SFR 8Bh
7
6
5
4
3
2
1
0
TL1.7
TL1.6
TL1.5
TL1.4
TL1.3
TL1.2
TL1.1
TL1.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Timer 1 LSB. This register contains the least significant byte of Timer 1.
TL1.7-0
Bits 7-0
Timer 0 MSB (TH0)
SFR 8Ch
7
6
5
4
3
2
1
0
TH0.7
TH0.6
TH0.5
TH0.4
TH0.3
TH0.2
TH0.1
TH0.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Timer 0 MSB. This register contains the most significant byte of Timer 0.
TH0.7-0
Bits 7-0
Timer 1 MSB (TH1)
SFR 8Dh
7
6
5
4
3
2
1
0
TH1.7
TH1.6
TH1.5
TH1.4
TH1.3
TH1.2
TH1.1
TH1.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Timer 1 MSB. This register contains the most significant byte of Timer 1.
TH1.7-0
Bits 7-0
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High-Speed Microcontroller User’s Guide
Clock Control (CKCON)
SFR 8Eh
7
6
5
4
3
2
1
0
WD1
WD0
T2M
T1M
T0M
MD2
MD1
MD0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-1
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
WD1, WD0
Bits 7-6
T2M
Bit 5
T1M
Bit 4
T0M
Bit 3
Watchdog Timer Mode Select 1-0. These bits determine the watchdog timer
time-out period. The timer divides the crystal frequency by a programmable
value as shown below. The divider value is expressed in clock (crystal) cycles.
The use of PMM1 or PMM2 will further divide the clock cycle count by either
16 or 256, respectively. Note that the reset time-out is 512 clocks longer than
the interrupt, regardless of whether the interrupt is enabled.
WD1
WD0
Interrupt Divider Reset Divider
0
0
217
217 + 512
20
220 + 512
0
1
2
1
0
223
223 + 512
1
1
226
226 + 512
Timer 2 Clock Select. This bit controls the division of the system clock that
drives Timer 2. This bit has no effect when the timer is in baud rate generator or
clock output modes. Clearing this bit to 0 maintains 80C32 compatibility. This
bit has no effect on instruction cycle timing.
0 = Timer 2 uses a divide by 12 of the crystal frequency.
1 = Timer 2 uses a divide by 4 of the crystal frequency.
Timer 1 Clock Select. This bit controls the division of the system clock that
drives Timer 1. Clearing this bit to 0 maintains 80C32 compatibility. This bit
has no effect on instruction cycle timing.
0 = Timer 1 uses a divide by 12 of the crystal frequency.
1 = Timer 1 uses a divide by 4 of the crystal frequency.
Timer 0 Clock Select. This bit controls the division of the system clock that
drives Timer 0. Clearing this bit to 0 maintains 80C32 compatibility. This bit
has no effect on instruction cycle timing.
0 = Timer 0 uses a divide by 12 of the crystal frequency.
1 = Timer 0 uses a divide by 4 of the crystal frequency.
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High-Speed Microcontroller User’s Guide
MD2, MD1, MD0
Bits 2-0
Stretch MOVX Select 2-0. These bits select the time by which external MOVX
cycles are to be stretched. This allows slower memory or peripherals to be
accessed without using ports or manual software intervention. The RD or WR
strobe will be stretched by the specified interval, which will be transparent to the
software except for the increased time to execute to MOVX instruction. All
internal MOVX instructions on devices containing MOVX SRAM are
performed at the 2 machine cycle rate.
MD2
MD1
MD0
Stretch Value MOVX Duration
0
0
0
0
2 Machine Cycles
0
0
1
1
3 Machine Cycles
(reset default)
0
1
0
2
4 Machine Cycles
0
1
1
3
5 Machine Cycles
1
0
0
4
6 Machine Cycles
1
0
1
5
7 Machine Cycles
1
1
0
6
8 Machine Cycles
1
1
1
7
9 Machine Cycles
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High-Speed Microcontroller User’s Guide
Port 1 (P1)
SFR 90h
7
6
5
4
3
2
1
0
P1.7
P1.5
INT5
P1.6
INT4
INT3
P1.4
INT2
P1.3
TXD1
P1.2
RXD1
P1.1
T2EX
P1.0
T2
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-1
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
P1.7-0
Bits 7-0
INT5
Bit 7
INT4
Bit 6
INT3
Bit 5
INT2
Bit 4
TXD1
Bit 3
RXD1
Bit 2
T2EX
Bit 1
T2
Bit 0
General Purpose I/O Port 1. This register functions as a general purpose I/O
port. In addition, all the pins have an alternative function listed below. P1.2-7
contain functions that are new to the 80C32 architecture. The Timer 2 functions
on pins P1.1-0 are available on the 80C32, but not the 80C31. Each of the
functions is controlled by several other SFRs. The associated Port 1 latch bit
must contain a logic one before the pin can be used in its alternate function
capacity.
External Interrupt 5. A falling edge on this pin will cause an external interrupt
5 if enabled.
External Interrupt 4. A rising edge on this pin will cause an external interrupt
4 if enabled.
External Interrupt 3. A falling edge on this pin will cause an external interrupt
3 if enabled.
External Interrupt 2. A rising edge on this pin will cause an external interrupt
2 if enabled.
Serial Port 1 Transmit. This pin transmits the serial port 1 data in serial port
modes 1, 2, 3 and emits the synchronizing clock in serial port mode 0.
Serial Port 1 Receive. This pin receives the serial port 1 data in serial port
modes 1, 2, 3 and is a bi-directional data transfer pin in serial port mode 0.
Timer 2 Capture/Reload Trigger. A 1 to 0 transition on this pin will cause the
value in the T2 registers to be transferred into the capture registers if enabled by
EXEN2 (T2CON.3). When in auto–reload mode, a 1 to 0 transition on this pin
will reload the timer 2 registers with the value in RCAP2L and RCAP2H if
enabled by EXEN2 (T2CON.3).
Timer 2 External Input. A 1 to 0 transition on this pin will cause timer 2
increment or decrement depending on the timer configuration.
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High-Speed Microcontroller User’s Guide
External Interrupt Flag (EXIF)
SFR 91h
7
6
5
4
3
2
1
0
IE5
IE4
IE3
IE2
XT/ RG
RGMD
RGSL
BGS
RW-0
RW-0
RW-0
RW-0
RW-*
R-*
RW-*
RT-0
R=Unrestricted Read, W=Unrestricted Write, T=Timed Access Write Only-n=Value after Reset,
*=See description
IE5
Bit 7
IE4
Bit 6
IE3
Bit 5
IE2
Bit 4
XT/ RG
Bit 3
RGMD
Bit 2
External Interrupt 5 Flag. This bit will be set when a falling edge is detected
on INT5 . This bit must be cleared manually by software. Setting this bit in
software will cause an interrupt if enabled.
External Interrupt 4 Flag. This bit will be set when a rising edge is detected on
INT4. This bit must be cleared manually by software. Setting this bit in software
will cause an interrupt if enabled.
External Interrupt 3 Flag. This bit will be set when a falling edge is detected
on INT3 . This bit must be cleared manually by software. Setting this bit in
software will cause an interrupt if enabled.
External Interrupt 2 Flag. This bit will be set when a rising edge is detected on
INT2. This bit must be cleared manually by software. Setting this bit in software
will cause an interrupt if enabled.
Crystal/Ring Source Select. This bit selects the crystal oscillator or ring
oscillator as the desired clock source. This bit will be the inverse of RGMD
except during the crystal warm-up period when executing a ring oscillator
resume from Stop. XTUP (STATUS.4) must be set to 1 and XTOFF (PMR.3)
must be cleared to 0 before this bit can be set. Attempts to modify this bit when
these conditions are not met will be ignored. This bit must be cleared before
XTOFF can be set to 1. This bit is set to 1 after a power-on reset, and unchanged
by all other forms of reset. This bit is not used on the DS80C310 or DS80C320
and will be 1 when read.
0 = The ring oscillator is selected as the clock source. This setting is unaffected
by XTUP (STATUS.4) and XTOFF (PMR.3).
1 = The crystal oscillator is selected as the clock source. This setting is invalid
unless XTUP=1 and XTOFF=0.
Ring Mode Status. This bit indicates the current clock source for the
device. This bit is cleared to 0 after a power-on reset, and unchanged by all
other forms of reset. The state of this bit will be undefined on devices which
do not incorporate a ring oscillator.
0 = Device is operating from the external crystal or oscillator.
1 = Device is operating from the ring oscillator.
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High-Speed Microcontroller User’s Guide
RGSL
Bit 1
BGS
Bit 0
Ring Oscillator Select. This bit selects the clock source following a resume
from Stop mode. Using the ring oscillator to resume from Stop mode allows
almost instantaneous start-up. This bit is cleared to 0 after a power-on reset, and
unchanged by all other forms of reset. The state of this bit will be undefined on
devices which do not incorporate a ring oscillator.
0 = The device will hold operation until the crystal oscillator has warmed-up.
1 = The device will begin operating from the ring oscillator, and when the crystal
warm-up is complete, will switch to the clock source indicated by the XT/ RG
bit.
Band-gap Select. This bit enables/disables the band-gap reference during Stop
mode. Disabling the band-gap reference provides significant power savings in
Stop mode, but sacrifices the ability to perform a power fail interrupt or powerfail reset while stopped. This bit can only be modified with a Timed Access
procedure. The state of this bit will be undefined on devices which do not
incorporate a band-gap reference.
0 = The band-gap reference is disabled in Stop mode but will function during
normal operation.
1 = The band-gap reference will operate in Stop mode.
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High-Speed Microcontroller User’s Guide
RTC Trim Register (TRIM)
SFR 91h
7
6
5
4
3
E4K
X12/ 6
TRM2
TRM2
TRM1
2
TRM1
1
0
TRM0
TRM0
RT-*
RT-*
RT-*
RT-*
RT-*
RT-*
RT-*
RT-*
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset, *=See description
E4K
Bit 7
X12/ 6
Bit 6
TRM2
Bit 5
TRM2
Bit 4
TRM1
Bit 3
TRM1
Bit 2
TRM0
Bit 1
TRM0
Bit 0
External 4096 Hz RTC Signal Enable. This bit enables the output of a
4096 Hz signal on pin P1.7 derived from the RTC. Setting this bit overrides
any other function of the pin. It is used for adjusting the frequency of the
32.768 RTC crystal oscillator using the trim bits. This bit is cleared to 0
after any reset, including a no-battery reset.
0 = Calibration function disabled. P1.7 pin will function per the normal pin
description.
1 = 4096 Hz signal output on P1.7
RTC Crystal Capacitance Select. This bit selects the internal loading
capacitance of the RTC crystal amplifier. This bit is set to 1 after a no-battery
reset, and unchanged by all other forms of reset.
0 = RTC loading is set for 6 pF crystal.
1 = RTC loading is set for 12.5 pF crystal.
RTC Trim Bit 2. This bit controls the relative adjustment of the RTC internal
capacitance. It is used to calibrate the RTC oscillator frequency. This bit is set to
1 after a no-battery reset, and unchanged by all other forms of reset.
RTC Trim Bit 2. This bit controls the relative adjustment of the RTC internal
capacitance. It is used to calibrate the RTC oscillator frequency. This bit is set to
1 after a no-battery reset, and unchanged by all other forms of reset.
RTC Trim Bit 1. This bit controls the relative adjustment of the RTC internal
capacitance. It is used to calibrate the RTC oscillator frequency. This bit is set to
0 after a no-battery reset, and unchanged by all other forms of reset.
RTC Inverted Trim Bit 1. This bit must always be set to the complement of
the TRM1 bit. Incorrectly writing this bit will default bits TRIM.7, TRIM.5-0 to
their no-battery reset value. This bit is cleared to 1 after a no-battery reset, and
unchanged by all other forms of reset.
RTC Trim Bit 0. This bit controls the relative adjustment of the RTC internal
capacitance. It is used to calibrate the RTC oscillator frequency. This bit is set to
0 after a no-battery reset, and unchanged by all other forms of reset.
RTC Inverted Trim Bit 0. This bit must always be set to the complement of
the TRM0 bit. Incorrectly writing this bit will default bits TRIM.7, TRIM.5-0 to
their no-battery reset value. This bit is cleared to 1 after a no-battery reset, and
unchanged by all other forms of reset.
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Serial Port 0 Control (SCON0)
SFR 98h
7
6
5
4
3
SM0/FE_0
SM1_0
SM2_0
REN_0
TB8_0
RW-0
RW-0
RW-0
RW-0
RW-0
2
RB8_0
RW-0
1
0
T1_0
R1_0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Serial Port Mode These bits control the mode of serial port 0. In addition the
SM0 and SM2_0 bits have secondary functions as shown below.
SM0-2
Bits 7-5
SM0
SM1
SM2
MODE
FUNCTION
LENGTH
PERIOD
0
0
0
0
Synchronous
8 bits
12 tCLK
0
0
1
0
Synchronous
8 bits
4 tCLK
0
1
X
1
Asynchronous
10 bits
Timer 1 or 2 baud rate equation
1
0
0
2
Asynchronous
11 bits
64 tCLK (SMOD=0)
32 tCLK (SMOD=1)
1
0
1
1
Asynchronous w/ Multiprocessor
communication
11 bits
64 tCLK (SMOD=0)
32 tCLK (SMOD=1)
1
1
0
3
Asynchronous
11 bits
Timer 1 or 2 baud rate equation
1
1
1
3
Asynchronous w/ Multiprocessor
communication
11 bits
Timer 1 or 2 baud rate equation
SM0/FE_0
Bit 7
SM1_0
Bit 6
SM2_0
Bit 5
Framing Error Flag. When SMOD0 (PCON.6)=0, this bit (SM0) is used to
select the mode for serial port 0. When SMOD0 (PCON.6)=1, this bit (FE) will
be set upon detection of an invalid stop bit. When used as FE, this bit must be
cleared in software. Once the SMOD0 bit is set, modifications to this bit will not
affect the serial port mode settings. Although accessed from the same register,
internally the data for bits SM0 and FE are stored in different locations.
No alternate function.
Multiple CPU Communications. The function of this bit is dependent on the
serial port 0 mode.
Mode 0: Selects 12 tCLK or 4 tCLK period for synchronous serial port 0 data
transfers.
Mode 1: When set, reception is ignored (RI_0 is not set) if invalid stop bit
received.
Mode 2/3: When this bit is set, multiprocessor communications are enabled in
modes 2 and 3. This will prevent the RI_0 bit from being set, and an interrupt
being asserted, if the 9th bit received is not 1.
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Receiver Enable. This bit enable/disables the serial port 0 receiver shift
register.
0 = Serial port 0 reception disabled.
1= Serial port 0 receiver enabled (modes 1, 2, 3). Initiate synchronous reception
(mode 0).
9th Transmission Bit State. This bit defines the state of the 9th transmission bit
in serial port 0 modes 2 and 3.
REN_0
Bit 4
TB8_0
Bit 3
RB8_0
Bit 2
9th Received Bit State. This bit identifies that state of the 9th reception bit of
received data in serial port 0 modes 2 and 3. In serial port mode 1, when
SM2_0=0, RB8_0 is the state of the stop bit. RB8_0 is not used in mode 0.
TI_0
Bit 1
Transmitter Interrupt Flag. This bit indicates that data in the serial port 0
buffer has been completely shifted out. In serial port mode 0, TI_0 is set at the
end of the 8th data bit. In all other modes, this bit is set at the end of the last data
bit. This bit must be manually cleared by software.
Receiver Interrupt Flag. This bit indicates that a byte of data has been
received in the serial port 0 buffer. In serial port mode 0, RI_0 is set at the end of
the 8th bit. In serial port mode 1, RI_0 is set after the last sample of the incoming
stop bit subject to the state of SM2_0. In modes 2 and 3, RI_0 is set after the last
sample of RB8_0. This bit must be manually cleared by software.
RI_0
Bit 0
Serial Data Buffer 0 (SBUF0)
7
SFR 99h SBUF0.7
RW-0
6
5
4
SBUF0.6
SBUF0.5
SBUF0.4
RW-0
RW-0
RW-0
3
2
SBUF0.3 SBUF0.2
RW-0
RW-0
1
0
SBUF0.1
SBUF0.0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Serial Data Buffer 0. Data for serial port 0 is read from or written to this
location. The serial transmit and receive buffers are separate registers, but both
are addressed at this location.
SBUF0.7-0
Bits 7-0
Port 2 (P2)
SFR A0h
7
6
5
4
3
2
1
0
P2.7
P2.6
P2.5
P2.4
P2.3
P2.2
P2.1
P2.0
RW-1
RW-1
RW-1
RW-1
RW-1
RW-1
RW-1
RW-1
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
P2.7-0
Bits 7-0
Port 2. This port functions as an address bus during external memory access,
and as a general purpose I/O port on devices which incorporate internal program
memory. During external memory cycles, this port will contain the MSB of the
address. The Port 2 latch does not control general purpose I/O pins on the
DS80C310 and DS80C320, but is still used to hold the address MSB during
register-indirect data memory operations such as MOVX A, @R1.
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Interrupt Enable (IE)
SFR A8h
7
6
5
4
3
2
1
0
EA
ES1
ET2
ES0
ET1
EX1
ET0
EX0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
EA
Bit 7
ES1
Bit 6
ET2
Bit 5
ES0
Bit 4
ET1
Bit 3
EX1
Bit 2
ET0
Bit 1
EX0
Bit 0
Global Interrupt Enable. This bit controls the global masking of all interrupts
except Power-Fail Interrupt, which is enabled by the EPFI bit (WDCON.5).
0 = Disable all interrupt sources. This bit overrides individual interrupt mask
settings.
1 = Enable all individual interrupt masks. Individual interrupts will occur if
enabled.
Enable Serial Port 1 Interrupt. This bit controls the masking of the serial port
1 interrupt.
0 = Disable all serial port 1 interrupts.
1 = Enable interrupt requests generated by the RI_1 (SCON1.0) or TI_1
(SCON1.1) flags.
Enable Timer 2 Interrupt. This bit controls the masking of the Timer 2
interrupt.
0 = Disable all Timer 2 interrupts.
1 = Enable interrupt requests generated by the TF2 flag (T2CON.7).
Enable Serial Port 0 Interrupt. This bit controls the masking of the serial port
0 interrupt.
0 = Disable all serial port 0 interrupts.
1 = Enable interrupt requests generated by the RI_0 (SCON0.0) or TI_0
(SCON0.1) flags.
Enable Timer 1 Interrupt. This bit controls the masking of the Timer 1
interrupt.
0 = Disable all Timer 1 interrupts.
1 = Enable all interrupt requests generated by the TF1 flag (TCON.7).
Enable External Interrupt 1. This bit controls the masking of external
interrupt 1.
0 = Disable external interrupt 1.
1 = Enable all interrupt requests generated by the INT0 pin.
Enable Timer 0 Interrupt. This bit controls the masking of the Timer 0
interrupt.
0 = Disable all Timer 0 interrupts.
1 = Enable all interrupt requests generated by the TF0 flag (TCON.5).
Enable External Interrupt 0. This bit controls the masking of external
interrupt 0.
0 = Disable external interrupt 0.
1 = Enable all interrupt requests generated by the INT0 pin.
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Slave Address Register 0 (SADDR0)
7
SFR A9h SADDR0.7
RW-0
6
5
4
3
2
1
0
SADDR0.6
SADDR0.5
SADDR0.4
SADDR0.3
SADDR0.2
SADDR0.1
SADDR0.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Slave Address Register 0. This register is programmed with the given or
broadcast address assigned to serial port 0.
SADDR0.7-0
Bits 7-0
Slave Address Register 1 (SADDR1)
SFR AAh
7
6
5
4
3
2
1
0
SADDR1.7
SADDR1.6
SADDR1.5
SADDR1.4
SADDR1.3
SADDR1.2
SADDR1.1
SADDR1.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
SADDR1.7-0
Bits 7-0
Slave Address Register 1. This register is programmed with the given or
broadcast address assigned to serial port 1.
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Port 3 (P3)
SFR B0h
7
6
5
4
3
2
1
0
P3.7
P3.5
T1
P3.4
T0
P3.3
P3.2
RD
P3.6
WR
INT 1
INT 0
P3.1
TXD0
P3.0
RXD0
RW-1
RW-1
RW-1
RW-1
RW-1
RW-1
RW-1
RW-1
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
P3.7-0
Bits 7-0
RD
Bit 7
Purpose I/O Port 3. This register functions as a general purpose I/O port. In
addition, all the pins have an alternative function listed below. Each of the
functions is controlled by several other SFRs. The associated Port 1 latch bit
must contain a logic one before the pin can be used in its alternate function
capacity.
External Data Memory Read Strobe. This pin provides an active low read
strobe to an external memory device.
Bit 6
External Data Memory Write Strobe. This pin provides an active low write
strobe to an external memory device.
T1
Bit 5
Timer/Counter External Input. A 1 to 0 transition on this pin will increment
Timer 1.
T0
Bit 4
Counter External Input. A 1 to 0 transition on this pin will increment Timer 0.
INT1
External Interrupt 1. A falling edge/low level on this pin will cause an
external interrupt 1 if enabled.
WR
Bit 3
INT0
Bit 2
TXD0
Bit 1
RXD0
Bit 0
External Interrupt 0. A falling edge/low level on this pin will cause an
external interrupt 0 if enabled.
Serial Port 0 Transmit. This pin transmits the serial port 0 data in serial port
modes 1, 2, 3 and emits the synchronizing clock in serial port mode 0.
Serial Port 0 Receive. This pin receives the serial port 0 data in serial port
modes 1, 2, 3 and is a bi-directional data transfer pin in serial port mode 0.
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Interrupt Priority (IP)
SFR B8h
7
6
5
4
3
2
1
0
-
PS1
PT2
PS0
PT1
PX1
PT0
PX0
-
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Bit 7
PS1
Bit 6
PT2
Bit 5
PS0
Bit 4
PT1
Bit 3
PX1
Bit 2
PT0
Bit 1
PX0
Bit 0
Reserved. Read data is indeterminate.
Serial Port 1 Interrupt. This bit controls the priority of the serial port 1
interrupt.
0 = Serial port 1 priority is determined by the natural priority order.
1 = Serial port 1 is a high priority interrupt.
Timer 2 Interrupt. This bit controls the priority of Timer 2 interrupt.
0 = Timer 2 is determined by the natural priority order.
1 = Timer 2 is a high priority interrupt.
Serial Port 0 Interrupt. This bit controls the priority of the serial port 0
interrupt.
0 = Serial port 0 priority is determined by the natural priority order.
1 = Serial port 0 is a high priority interrupt.
Timer 1 Interrupt. This bit controls the priority of Timer 1 interrupt.
0 = Timer 1 is determined by the natural priority order.
1 = Timer 1 is a high priority interrupt.
External Interrupt 1. This bit controls the priority of external interrupt 1.
0 = External interrupt 1 is determined by the natural priority order.
1 = External interrupt 1 is a high priority interrupt.
Timer 0 Interrupt. This bit controls the priority of Timer 0 interrupt.
0 = Timer 0 is determined by the natural priority order.
1 = Timer 0 is a high priority interrupt.
External Interrupt 0. This bit controls the priority of external interrupt 0.
0 = External interrupt 0 is determined by the natural priority order.
1 = External interrupt 0 is a high priority interrupt.
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Slave Address Mask Enable Register 0 (SADEN0)
SFR B9h
7
6
5
4
3
2
1
0
SADEN0.7
SADEN0.6
SADEN0.5
SADEN0.4
SADEN0.3
SADEN0.2
SADEN0.1
SADEN0.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Slave Address Mask Enable Register 0. This register functions as a mask
when comparing serial port 0 addresses for automatic address recognition.
When a bit in this register is set, the corresponding bit location in the SADDR0
register will be exactly compared with the incoming serial port 0 data to
determine if a receiver interrupt should be generated. When a bit in this register
is cleared, the corresponding bit in the SADDR0 register becomes a don‘t care
and is not compared against the incoming data. All incoming data will generate
a receiver interrupt when this register is cleared.
SADEN0.7-0
Bits 7-0
Slave Address Mask Enable Register 1 (SADEN1)
7
SFR BAh SADEN1.7
RW-0
6
5
4
3
2
1
0
SADEN1.6
SADEN1.5
SADEN1.4
SADEN1.3
SADEN1.2
SADEN1.1
SADEN1.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
SADEN1.7-0
Bits 7-0
Slave Address Mask Enable Register 1. This register functions as a mask
when comparing serial port 1 addresses for automatic address recognition. When
a bit in this register is set, the corresponding bit location in the SADDR1 register
will be exactly compared with the incoming serial port 1 data to determine if a
receiver interrupt should be generated. When a bit in this register is cleared, the
corresponding bit in the SADDR1 register becomes a don’t care and is not
compared against the incoming data. All incoming data will generate a receiver
interrupt when this register is cleared.
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Serial Port Control (SCON1)
SFR C0h
7
6
5
4
3
SM0/FE_1
SM1_1
SM2_1
REN_1
TB8_1
RW-0
RW-0
RW-0
RW-0
RW-0
2
RB8_1
RW-0
1
0
TI_1
RI_1
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Serial Port 1 Mode. These bits control the mode of serial port 1 as shown
below. In addition, the SM0 and SM2 bits have secondary functions as Shown
below.
SM0-2
Bits 7-5
SM0
SM1
SM2
MODE
0
0
0
0
Synchronous
8 bits
12tCLK
0
0
1
0
Synchronous
8 bits
4tCLK
0
1
X
1
Asynchronous
10 bits
Timer 1 baud rate
equation
1
0
0
2
Asynchronous
11 bits
64tCLK (SMOD=0)
32tCLK (SMOD=1)
1
0
1
2
Asynchronous w/ Multiprocessor
communication
11 bits
64tCLK (SMOD=0)
32tCLK (SMOD=1)
1
1
0
3
Asynchronous
11 bits
Timer 1 baud rate
equation
1
1
1
3
Asynchronous w/ Multiprocessor
communication
11 bits
Timer 1 baud rate
equation
SM0/FE_1
Bit 7
SM1_1
Bit 6
SM2-2
Bit 5
FUNCTION
LENGTH
PERIOD
Framing Error Flag. When SMOD0 (PCON.6)=0, this bit (SM0) is used to
select the mode for serial port 1. When SMOD0 (PCON.6)=1, this bit (FE) will
be set upon detection of an invalid stop bit. When used as FE, this bit must be
cleared in software. Once the SMOD0 bit is set, modifications to this bit will
not affect the serial port mode settings. Although accessed from the same
register, internally the data for bits SM0 and FE are stored in different locations.
No alternate function.
Multiple CPU Communications. The function of this bit is dependent on the
serial port 1 mode.
Mode 0: Selects 12 tCLK or 4tCLK period for synchronous port 1 data transfers.
Mode 1: When this bit is set, reception is ignored (RI_1) is not set) if invalid
stop bit received.
Mode 2/3: when this bit is set, multiprocessor communications are enabled in
mode 2 and 3. This will prevent RI_1 from being set, and an interrupt being
asserted, if the 9th bit received is not 1.
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Receive Enable. This bit enables/disables the serial port 1 receiver shift
register.
0 = Serial port 1 reception disabled.
1 = Serial port 1 receiver enabled (modes 1, 2, 3). Initiate synchronous reception
(mode 0).
9th Transmission Bit State. This bit defines the state of the 9th transmission bit
in serial port 1 modes 2 and 3.
REN_1
Bit 4
TB8_1
Bit 3
9th Received Bit State. This bit identifies the state for the 9th reception bit
received data in serial pot 1 modes 2 and 3. In serial port mode 1, when
SM2_1=0, RB8_1 is the state of the stop bit. RB8_1 is not used in mode 0.
Transmitter Interrupt Flag. This bit indicates that data in the serial port 1
buffer has been completely shifted out. In serial port mode 0, TI_1 is set at the
end of the 8th data bit. In all other modes, this bit is set at the end of the last data
bit. This bit must be manually cleared by software.
Transmitter Interrupt Flag. This bit indicates that a byte of data has been
received in the serial port 1 buffer. In serial port mode 1, RI_1 is set at the end
of the 8th bit. In serial port mode 1, RI_1 is set after the last sample of the
incoming stop bit subject to the state of SM2_1. In modes 2 and 3, RI_1 is set
after the last sample of RB8_1. This bit must be manually cleared by software.
RB8_1
Bit 2
TI_1
Bit 1
RI_1
Bit 0
Serial Data Buffer 1 (SBUF1)
7
SFR C1h SBUF1.7
RW-0
6
5
4
3
2
SBUF1.6
SBUF1.5
SBUF1.4
SBUF1.3
SBUF1.2
RW-0
RW-0
RW-0
RW-0
RW-0
1
0
SBUF1.1 SBUF1.0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
SBUF1.7-0
Bits 7-0
Serial Data Buffer 1. Data for serial port 1 is read from or written to this
location. The serial transmit and receive buffers are separate registers, but both
are addressed at this location.
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ROM Size Select (ROMSIZE)
SFR C2h
7
6
5
4
3
2
1
0
-
-
-
-
-
RS2
RS1
RS0
RT-1
RT-0
RT-1
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Bits 7-3
These bits are reserved. Read data is indeterminate.
ROMSIZE.2-0
ROM Size Select 2-0. This register is used to select the maximum on-chip
decoded address for ROM. Care must be taken that the memory location of the
current program counter will be valid both before and after modification. These
bits can only be modified using a timed access procedure. The EA pin will
override the function of these bits when asserted, forcing the device to access
external program memory only. Configuring this register to a setting that
exceeds the maximum amount of internal memory may corrupt device operation.
These bits will default on reset to the maximum amount of internal program
memory (i.e., 16K for DS87C520).
Bits 2-0
RS2
RS1
RS0
MAXIMUM ON-CHIP ROM ADDRESS
0
0
0
0KB/Disable on-chip ROM
0
0
1
1KB/03FFh
0
1
0
2KB/07FFh
0
1
1
4KB/0FFFh
1
0
0
8KB/1FFFh
1
0
1
16KB/3FFFh
1
1
0
132KB/7FFFh
1
1
1
64KB/FFFFh
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Power Management Register (PMR)
SFR C4h
7
6
5
4
3
2
1
0
CD1
CD0
SWB
-
XTOFF
ALEOFF
DME1
DME0
RW-0
RW-1
RW-0
RW*-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset, *=See description
Clock Divide Control 1-0. These bits select the number of crystal oscillator
clocks required to generate one machine cycle. Switching between modes
requires a transition through the divide by 4 mode (CD1, CD0=01). For
example, to go from 64 to 1024 clocks per cycle the device must first go from 64
to 4 clocks per cycle, and then from 4 to 1024 clocks per cycle. Attempts to
perform an invalid transition will be ignored. The setting of these bits will effect
the timers and serial ports as shown below.
CD1, CD0
Bits 7-6
OSC
CYCLES
PER
MACH.
CYCLE
OSC CYCLES
PER TIMER 2
CLK, BAUD
RATE GEN.
TxM=0
TxM=1
OSC CYCLES
PER SERIAL
PORT CLK,
MODE 0
CD1
CD0
T2M=0
0
0
0
1
4
12
4
2
1
0
64
192
64
1
1
1024
3072
1024
T2M=1
OSC CYCLES
PER TIMER 2
CLK, BAUD
RATE GEN.
OSC CYCLES PER
SERIAL PORT CLK,
MODE 2
SM2=0
SM2=1
SDMO=0
SMOD=1
2
12
4
64
32
32
32
194
64
1024
512
512
512
3072
1024
16384
8192
RESERVED
SWB
Bit 5
Switchback Enable. This bit allows an enabled external interrupt or serial port
activity to force the Clock Divide Control bits to the divide by 4 state (01).
Upon internal acknowledgement of an external interrupt, the device will switch
modes at the start of the jump to the interrupt service routine. Note that this
means that an external interrupt must actually be recognized (i.e., be enabled and
not masked by higher priority interrupts) for the switchback to occur. For serial
port reception, the switch occurs at the start of the instructions following the
falling edge of the start bit.
Bit 4
Reserved. When modifying the PMR register, software must write a 0 to this
bit. Read data will be indeterminate.
XTOFF
Bit 3
Crystal Oscillator Disable. This bit disables the CPU crystal oscillator. It can
only be set to 1 while running the ring oscillator (XT/ RG =0). Clearing this bit
restarts the crystal amplifier, reset the crystal warm-up counter, and after 65,536
external crystal cycles the XTUP bit will be set.
0 = Crystal oscillator is enabled.
1 = Crystal oscillator is disabled.
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ALE Disable. This bit disables the expression of the ALE signal on the device
pin during all on-board program and data memory accesses. External memory
accesses will automatically enable ALE independent of ALEOFF.
0 = ALE expression is enabled.
1 = ALE expression is disabled.
Data Memory Enable 1-0. These bits determine the functional relationship of
the first 1024 bytes of data memory. Three memory configurations are
supported to allow either external data memory access through the expanded
multiplexed address/data bus of Ports 0 and Port 2, internal SRAM data memory
access, or read-only access to EPROM programming information. Note these
bits are cleared after a reset, so access to the internal SRAM is prohibited until
these bits are modified.
ALEOFF
Bit 2
DME1, DME0
Bit 1
DME1
0
0
DME0
0
1
1
1
0
1
DATA MEMORY
ADDRESS RANGE
0000h – FFFFh
0000h – 03FFh
0400h - FFFFh
Reserved
0000h – 03FFh
0400h – FFFBh
FFFCh
FFFDh - FFFFh
MEMORY ACCESS
External Data Memory (default)
Internal SRAM data Memory
External Data Memory
Reserved
Internal SRAM data Memory
Reserved
System Control Byte (EPROM Read Only)
Reserved
The System Control Byte is a special EPROM location that contains nonvolatile
system information. This byte is set during EPROM programming and is not
alterable by software. This register can only be read when both Data Memory
Enable bits are set. The user must be sure that this location is programmed by the
of a special programming utility supplied with the programming device.
System Control Byte Description 9EPROM; FFFCh)
Bits 7-3
Reserved. These bits will read 1. These bits should be set to 1 during EPROM
programming.
EPROM Program Lock Bit 301. These bits show the status of the firmware
security of the on-board EPROM. Bit combinations other than shown are illegal.
LB3, LB2, LB1
Bits 2-0
LB3 LB2 LB1
0
0
0
0
0
1
0
1
1
1
1
1
EPROM PROTECTION MODE
Unconditional verification, full external operation. Additional EPROM programming
allowed without full device erasure.
Verification using encryption, execution of external MOVC instruction on internal
program memory is disabled. All other program execution and data memory access
allowed. Device must be fully erased before EPROM can be programmed again.
Verification disabled, execution of external MOVC instruction on internal program
memory is disabled, and access to internal MOVX data from external program is
prohibited. All other program execution and data memory access allowed. Device must
be fully erased before EPROM can be programmed again.
Verification disabled, external program execution prohibited. Device must be fully
erased before EPROM can be programmed again.
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Status Register (STATUS)
SFR C5
7
6
5
4
3
2
1
0
PIP
HIP
LIP
XTUP
SPTA1
SPRA1
SPTA0
SPRA0
R-0
R-0
R-0
R-0*
R-0
R-0
R-0
R-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset, *=See description
PIP
Bit 7
HP
Bit 6
LIP
Bit 5
XTUP
Bit 4
SPTA1
Bit 3
SPRA1
Bit 2
SPTA0
Bit 1
SPRA0
Bit 0
Power Fail Priority Interrupt Status. When set, this bit indicates that software
is currently servicing a power-fail interrupt. It is cleared when the program
executes the corresponding RETI instruction. This bit is indeterminate on
devices which do not incorporate the power-fail interrupt.
High Priority Interrupt Status. When set, this bit indicates that software is
currently servicing a high priority interrupt. It is cleared when the program
executes the corresponding RETI instruction.
Low Priority Interrupt Status. When set, this bit indicates that software is
currently servicing a low priority interrupt. It is cleared when the program
executes the corresponding RETI instruction.
Crystal Oscillator Warm-up Status. This bit indicates whether the CPU
crystal oscillator has completed the 65,536 cycle warm-up and is ready to
operate from the external crystal or oscillator. This bit is cleared each time the
crystal oscillator is restarted following an exit from Stop mode or the XTOFF bit
(PMR.3) is set. While cleared, this bit prevents software from setting the XT/ RG
bit (EXIF.3) to enable operation from the crystal. Note that XTUP differs from
the RGMD bit (EXIF.2) in that XTUP shows the status of the crystal while
RGMD shows the current clock source. This bit is set to 1 following a power–on
reset, but is unaffected by other forms of reset.
Serial Port 1 Transmit Activity Monitor. When set, this bit indicates that data
is currently being transmitted by serial port 1. It is cleared when the internal
hardware sets the TI_1 bit. Do not alter the Clock Divide Control bits (PMR.7-6)
while this bit is set or serial port data may be lost.
Serial Port 1 Receive Activity Monitor. When set, this bit indicates that data is
currently being received by serial port 1. It is cleared when the internal hardware
sets the RI_1 bit. Do not alter the Clock Divide Control bits (PMR.7–6) while
this bit is set or serial port data may be lost.
Serial Port 0 Transmit Activity Monitor. When set, this bit indicates that data
is currently being transmitted by serial port 0. It is cleared when the internal
hardware sets the TI_1 bit. Do not alter the Clock Divide Control bits (PMR.7-6)
while this bit is set or serial port data may be lost.
Serial Port 0 Receive Activity Monitor. When set, this bit indicates that data is
currently being received by serial port 0. It is cleared when the internal hardware
sets the RI_1 bit. Do not alter the Clock Divide Control bits (PMR.7-6) while
this bit is set or serial port data may be lost.
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Time Access Register (TA)
SFR C7h
7
6
5
4
3
2
1
0
TA.7
TA.6
TA.5
TA.4
TA.3
TA.2
TA.1
TA.0
W-1
W-1
W-1
W-1
W-1
W-1
W-1
W-1
W=Unrestricted Write, -n=Value after Reset
Timed Access. Correctly accessing this register permits modification of timed
access protected bits. Write AAh to this register first, followed within 3 cycles
by writing 55h. Timed access protected bits can then be modified for a period of
3 cycles measured from the writing of the 55h.
TA.7-0
Bits 7-0
Time 2 Control (T2CON)
SFR C8h
7
6
5
4
3
2
1
0
TF2
EXF2
RCLK
TCLK
EXEN2
TR2
C/ T2
CP/RL2
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
TF2
Bit 7
EXF2
Bit 6
CP/ RL2
1
1
0
0
0
RCLK
Bit 5
Timer 2 Overflow Flag. This flag will be set when Timer 2 overflows from
FFFFh or the count equal to the capture register in down count mode. It must be
cleared by software. TF2 will only be set if RCLK and TCLK are both cleared to
0.
Timer 2 External Flag. A negative transition on the T2EX pin (P1.1) or timer 2
underflow/overflow will cause this flag to set based on the CP/ RL2 (T2CON.0),
EXEN2 (T2CON.3), and DCEN (T2MOD.0) bits. If set by a negative transition,
this flag must be cleared to 0 by software. Setting this bit in software or
detection of a negative transition on the T2EX pin will force a timer interrupt if
enabled.
EXEN2
0
1
0
1
X
DCEN
X
X
0
0
1
RESULT
Negative transitions on P1.1 will not affect this bit.
Negative transitions on P1.1 will set this bit.
Negative transitions on P1.1 will not affect this bit.
Negative transitions on P1.1 will set this bit.
Bit toggles whenever timer 2 underflows/overflows
and can be used as a 17th bit of resolution. In this
mode, EXF2 will not cause an interrupt.
Receive Clock Flag. This bit determines the serial port 0 timebase when
receiving data in serial modes 1 or 3.
0 = Timer 1 overflow is used to determine receiver baud rate for serial port 0.
1 = Timer 2 overflow is used to determine receiver baud rate for serial port 0.
Setting this bit will force timer 2 into baud rate generation mode. The timer
will operate from a divide by 2 of the external clock.
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TCLK
Bit 4
EXEN2
Bit 3
TR2
Bit 2
C/ T2
Bit 1
CP/ RL2
Bit 0
Transmit Clock Flag. This bit determines the serial port 0 timebase when
transmitting data in serial modes 1 or 3.
0 = Timer 1 overflow is used to determine transmitter baud rate for serial port 0.
1 = Timer 2 overflow is used to determine transmitter baud rate for serial port 0.
Setting this bit will force timer 2 into baud rate generation mode. The timer will
operate from a divide by 2 of the external clock.
Timer 2 External Enable. This bit enables the capture/ reload function on the
T2EX pin if Timer 2 is not generating baud rates for the serial port.
0 = Timer 2 will ignore all external events at T2EX.
1 = Timer 2 will capture or reload a value if a negative transition is detected on
the T2EX pin.
Timer 2 Run Control. This bit enables/disables the operation of timer 2.
Halting this timer will preserve the current count in TH2, TL2.
0 = Timer 2 is halted.
1 = Timer 2 is enabled.
Counter/Timer Select. This bit determines whether timer 2 will function as a
timer or counter. Independent of this bit, timer 2 runs at 2 clocks per tick when
used in either baud rate generator or clock output mode.
0 = Timer 2 function as a timer. The speed of timer 2 is determined by the T2M
bit (CKCON.5).
1 = Timer 2 will count negative transitions on the T2 pin (P1.0).
Capture/Reload Select. This bit determines whether the capture or reload
function will be used for timer 2. If either RCLK or TCLK is set, this bit will not
function and the timer will function in an auto-reload mode following each
overflow.
0 = Auto-reloads will occur when timer 2 overflows or a falling edge is detected
on T2EX if EXEN2=1.
1 = Timer 2 captures will occur when a falling edge is detected on T2EX if
EXEN2 = 1.
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Timer 2 Mode (T2MOD)
SFR C9h
7
6
5
4
3
2
1
0
-
-
-
-
-
-
T2OE
DCEN
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Bits 7-2
T2OE
Bit 1
Reserved. Read data will be indeterminate.
Timer 2 Output Enable. This bit enables/disables the clock output function of
the T2 pin (P1.0). 0 = The T2 pin functions as either a standard port pin or as a
counter input for timer 2. 1 = Timer 2 will drive the T2 pin with a clock output
if C/ T2 =0. Also, timer 2 rollovers will not cause interrupts.
Down Count Enable. This bit, in conjunction with the T2EX pin, controls the
direction that timer 2 counts in 16-bit auto-reload mode.
DCEN
Bit 0
DCEN
1
1
0
T2EX
1
0
X
DIRECTION
Up
Down
Up
Timer 2 Capture LSB (RCAP2L)
SFR CAh
7
6
5
4
3
2
1
0
RCAP2L.7
RCAP2L.6
RCAP2L.5
RCAP2L.4
RCAP2L.3
RCAP2L.2
RCAP2L.1
RCAP2L.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Timer 2 Capture LSB. This register is used to capture the TL2 value when
timer 2 is configured in capture mode. RCAP2L is also used as the LSB of a 16bit reload value when timer 2 is configured in auto-reload mode.
RCAP2L.7-0
Bits 7-0
Timer 2 Capture MSB (RCAP2H)
7
SFR CBh RCAP2H.7
RW-0
6
5
4
3
2
1
0
RCAP2H.6
RCAP2H.5
RCAP2H.4
RCAP2H.3
RCAP2H.2
RCAP2H.1
RCAP2H.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
RCAP2H.7-0
Bits 7-0
Timer 2 Capture MSB. This register is used to capture the TH2 value when
timer 2 is configured in capture mode. RCAP2H is also used as the MSB of a 16bit reload value when timer 2 is configured in auto-reload mode.
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Timer 2 LSB (TL2)
SFR CCh
7
6
5
4
3
2
1
0
TL2.7
TL2.6
TL2.5
TL2.4
TL2.3
TL2.2
TL2.1
TL2.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Timer 2 LSB. This register contains the least significant byte of Timer 2.
TL2.7-0
Bits 7-0
Timer 2 MSB (TH2)
SFR CDh
7
6
5
4
3
2
1
0
TH2.7
TH2.6
TH2.5
TH2.4
TH2.3
TH2.2
TH2.1
TH2.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
TL2.7-0
Bits 7-0
Timer 2 MSB. This register contains the least significant byte of Timer 2.
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Program Status Word (PSW)
SFR D0h
7
6
5
4
3
2
1
0
CY
AC
F0
RS1
RS0
0V
F1
PARITY
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
CY
Bit 7
Carry Flag. This bit is set when if the last arithmetic operation resulted in a
carry (during addition) or a borrow (during subtraction). Otherwise it is cleared
to 0 by all arithmetic operations.
AC
Bit 6
Auxiliary Carry Flag. This bit is set to 1 if the last arithmetic operation
resulted in a carry into (during addition), or a borrow (during subtraction) from
the high order nibble. Otherwise it is cleared to 0 by all arithmetic operations.
F0
Bit 5
User Flag 0. This is a bit-addressable, general purpose flag for software control.
RS1, RS0
Bits 4-3
Register Bank Select 1–0. These bits select which register bank is addressed
during register accesses.
OV
Bit 2
F1
Bit 1
PARITY
Bit 0
RS1
RS0
REGISTER BANK
ADDRESS
0
0
0
00h – 07h
0
1
1
08h – 0Fh
1
0
2
10h – 17h
1
1
3
18h – 1Fh
Overflow Flag. This bit is set to 1 if the last arithmetic operation resulted in a
carry (addition), borrow (subtraction), or overflow (multiply or divide).
Otherwise it is cleared to 0 by all arithmetic operations.
User Flag 1. This is a bit-addressable, general purpose flag for software control.
Parity Flag. This bit is set to 1 if the modulo-2 sum of the eight bits of the
accumulator is 1 (odd parity); and cleared to 0 on even parity.
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Watchdog Control (WDCON)
SFR D8h
7
6
5
4
3
2
1
0
SMOD
POR
EPF1
PFI
WDIF
WTRF
EWT
RWT
RW-0
RW-*
RW-0
RW-*
RW-0
RW-*
RW-*
RW-0
R=Unrestricted Read, W=Unrestricted Write, T=Timed Access Write Only,
-n=Value after Reset, *=See Description
SMOD
Bit 7
Serial Modification. This bit controls the doubling of the serial port 1 baud rate
in modes 1, 2, and 3.
0 = Serial port 1 baud rate operates at normal speed
1 = Serial port 1 baud rate is doubled.
POR
Bit 6
Power-on Reset Flag. This bit indicates whether the last reset was a power-on
reset. This bit is typically interrogated following a reset to determine if the reset
was caused by a power-on reset. It must be cleared by a Timed Access write
before the next reset of any kind or the software may erroneously determine that
another power-on reset has occurred. This bit is set following a power-on reset
and unaffected by all other resets. Note: This bit is not Timed Access protected
on the DS80C310.
0 = Last reset was from a source other than a power-on reset
EPFI
Bit 5
1 = Last reset was a power-on reset.
Enable Power fail Interrupt. This bit enables/disables the ability of the internal
band-gap reference to generate a power-fail interrupt when VCC falls below
approximately 4.5 volts. While in Stop mode, both this bit and the Band-gap
Select bit, BGS (EXIF.0), must be set to enable the power-fail interrupt.
0 = Power-fail interrupt disabled.
1 = Power-fail interrupt enabled during normal operation. Power-fail interrupt
enabled in Stop mode if BGS is set.
PFI
Bit 4
Power fail Interrupt Flag. When set, this bit indicates that a power-fail
interrupt has occurred. This bit must be cleared in software before exiting the
interrupt service routine, or another interrupt will be generated. Setting this bit in
software will generate a power-fail interrupt, if enabled.
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WDIF
Bit 3
Watchdog Interrupt Flag. This bit, in conjunction with the Watchdog Timer
Interrupt Enable bit, EWDI (EIE.4), and Enable Watchdog Timer Reset bit
(WDCON.1), indicates if a watchdog timer event has occurred and what action
will be taken. This bit must be cleared in software before exiting the interrupt
service routine, or another interrupt will be generated. Setting this bit in
software will generate a watchdog interrupt if enabled. This bit can only be
modified using a Timed Access Procedure.
EWT
X
0
EWDI
X
0
WDIF
0
1
0
1
1
0
1
1
1
1
1
RESULT
No watchdog event has occurred.
Watchdog time-out has expired. No interrupt has been
generated.
Watchdog interrupt has occurred.
Watchdog time-out has expired. No interrupt has been
generated. Watchdog timer reset will occur in 512 cycles
if RWT is not strobed.
Watchdog interrupt has occurred. Watchdog timer reset
will occur in 512 cycles if RWT is not set using a Timed
Access procedure.
WTRF
Bit 2
Watchdog Timer Reset Flag. When set, this bit indicates that a watchdog timer
reset has occurred. It is typically interrogated to determine if a reset was caused
by watchdog timer reset. It is cleared by a power- on reset, but otherwise must be
cleared by software before the next reset of any kind or software may
erroneously determine that a watchdog timer reset has occurred. Setting this bit
in software will not generate a watchdog timer reset. If the EWT bit is cleared,
the watchdog timer will have no effect on this bit.
EWT
Bit 1
Enable Watchdog Timer Reset. This bit enables/disables the ability of the
watchdog timer to reset the device. This bit has no effect on the ability of the
watchdog timer to generate a watchdog interrupt. The time-out period of the
watchdog timer is controlled by the Watchdog Timer Mode Select bits
(CKCON.7-6). Clearing this bit will disable the ability of the watchdog timer to
generate a reset, but have no affect on the timer itself, or its ability to generate a
watchdog timer interrupt. This bit can only be modified using a Timed Access
Procedure. The default power-on reset state of this bit is 0 on the ROMless
devices. If the device contains internal program memory, the default power-on
reset state of EWT is determined by the Watchdog Default POR State bit
(WDPOR) located in the System Control Byte or a mask option. This bit is
unaffected by all other resets.
0 = A timeout of the watchdog timer will not cause the device to reset.
1 = A timeout of the watchdog timer will cause the device to reset.
RWT
Bit 0
Reset Watchdog Timer. Setting this bit will reset the watchdog timer count.
This bit must be set using a Timed Access procedure before the watchdog timer
expires, or a watchdog timer reset and/or interrupt will be generated if enabled.
The time-out period is defined by the Watchdog Timer Mode Select bits
(CKCON.7-6). This bit will always be 0 when read.
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Accumulator (A or ACC)
SFR E0h
7
6
5
4
3
2
1
0
ACC.7
ACC.6
ACC.5
ACC.4
ACC.3
ACC.2
ACC.1
ACC.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Accumulator. This register serves as the accumulator for arithmetic operations.
It is functionally identical to the accumulator found in the 80C32.
ACC.7-0
Bits 7-0
Extended Interrupt Enable (EIE)
SFR E8h
7
6
5
4
3
2
1
0
-
-
ERTCI
EWDI
EX5
EX4
EX3
EX0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
Bit 7-0
Reserved. Read data will be indeterminate.
ERTCI
Bit 5
Real Time Clock Interrupt Enable. This bit enables/disables the real-time
clock interrupt on the DS87C530. This bit will read 0 on all other devices.
0 = Disable the real-time clock interrupt.
1 = Enable interrupt requests generated by the real-time clock.
EWDI
Bit 4
Watchdog Interrupt Enable. This bit enables/disables the watchdog interrupt.
0 = Disable the watchdog interrupt.
1 = Enable interrupt requests generated by the watchdog timer.
EX5
Bit 3
External Interrupt 5 Enable. This bit enables/disables external interrupt 5.
0 = Disable external interrupt 5.
EX4
Bit 2
EX3
Bit 1
EX2
Bit 0
1 = Enable interrupt requests generated by the INT5 pin.
External Interrupt 4 Enable. This bit enables/disables external interrupt 4.
0 = Disable external interrupt 4.
1 = Enable interrupt requests generated by the INT4 pin.
External Interrupt 3 Enable. This bit enables/disables external interrupt 3.
0 = Disable external interrupt 3. 1 = Enable interrupt requests generated by the
INT3 pin.
External Interrupt 2 Enable. This bit enables/disables external interrupt 2.
0 = Disable external interrupt 2.
1 = Enable interrupt requests generated by the INT2 pin.
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B Register (B)
SFR F0h
7
6
5
4
3
2
1
0
B.7
B.6
B.5
B.4
B.3
B.2
B.1
B.0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
B Register. This register serves as a second accumulator for certain arithmetic
operations. It is functionally identical to the B register found in the 80C32.
B.7-0
Bits 7-0
Real Time Alarm Subsecond Register (RTASS)
SFR F2h
7
6
5
4
3
2
1
0
RTASS.7
RTASS.6
RTASS.5
RTASS.4
RTASS.3
RTASS.2
RTASS.1
RTASS.0
RW-*
RW-*
RW-*
RW-*
RW-*
RW-*
RW-*
RW-*
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset, * = See description
Real Time Alarm Subsecond. These bits represent the subsecond alarm which
will be compared against the RTC Subsecond register (RTCSS;FAh). The
ability of a match between the two registers to cause an alarm is controlled by
the RTC Subsecond Register Compare Enable bit (RTCC.7). The contents of
this register will be indeterminate following a no-battery reset, and unchanged
by all other forms of reset.
RTASS.7-0
Bits 7-0
Real Time Alarm Second Register (RTAS)
SFR F3h
7
6
5
4
3
2
1
0
0
0
RTAS.5
RTAS.4
RTAS.3
RTAS.2
RTAS.1
RTAS.0
RW-0
RW-0
RW-*
RW-*
RW-*
RW-*
RW-*
RW-*
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset, * = See description
Bits 7-6
RTAS.5-0
Bits 5-0
Reserved. These bits will be 0 when read.
Real Time Alarm Second. These bits represent the second alarm which will be
compared against the RTC Second register (RTCS;FBh). The ability of a match
between the two registers to cause an alarm is controlled by the RTC Second
Register Compare Enable bit (RTCC.6). This register should only be loaded
with values from 0 to 3Bh (0 to 59 seconds). The contents of this register will be
indeterminate following a no-battery reset (except bits 7, 6), and unchanged by
all other forms of reset.
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Real Time Alarm Minute Register (RTAM)
SFR F4h
7
6
5
4
3
2
1
0
0
0
RTAM.5
RTAM.4
RTAM.3
RTAM.2
RTAM.1
RTAM.0
R-0
R-0
RW-*
RW-*
RW-*
RW-*
RW-*
RW-*
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset, * = See Description
Bits 7-6
Reserved. These bits will be 0 when read.
RTAM.5-0
Bits 5-0
Real Time Alarm Minute. These bits represent the minute alarm which will be
compared against the RTC Minute register (RTCM;FCh). The ability of a match
between the two registers to cause an alarm is controlled by the RTC Minute
Register Compare Enable bit (RTCC.5). This register should only be loaded
with values from 0 to 3Bh (0 to 59 minutes). The contents of this register will be
indeterminate following a no-battery reset (except bits 7, 6), and unchanged by
all other forms of reset.
Real Time Alarm Hour Register (RTAH)
SFR F5h
7
6
5
4
3
2
1
0
0
0
0
RTAH.4
RTAH.3
RTAH.2
RTAH.1
RTAH.0
R-0
R-0
R-0
RW-*
RW-*
RW-*
RW-*
RW-*
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset, * = See Description
Bits 7-5
Reserved. These bits will be 0 when read.
RTAH.4-0
Bits 4-0
Real Time Alarm Hour. These bits represent the hour alarm which will be
compared against the RTC Hour register (RTCH;FDh). The ability of a match
between the two registers to cause an alarm is controlled by the RTC Hour
Register Compare Enable bit (RTCC.4). This register should only be loaded
with values from 0 to 17h (0 to 23 hours). The day of week bits DOW2-0,
located in RTCH.7-5 do not have a corresponding alarm feature. The contents
of this register will be indeterminate following a no-battery reset (except bits 7,
6, 5), and unchanged by all other forms of reset.
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Extended Interrupt Priority (EIP)
SFR F8h
7
6
5
4
3
2
1
0
-
-
PRTCI
PWDI
PX5
PX4
PX3
PX2
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
R=Unrestricted Read, W=Unrestricted Write, -n = Value after Reset
Bits 7-6
Reserved. These bits will be 0 when read.
PRTCI
Bit 5
Real Time Clock Interrupt Priority. This bit controls the priority of the real–
time clock interrupt on the DS87C530. This bit will read 0 on all other devices.
0 = The real-time clock interrupt is a low priority interrupt.
1 = The real-time clock interrupt is a high priority interrupt.
PWDI
Bit 4
Interrupt Priority. This bit controls the priority of the watchdog interrupt.
0 = The watchdog interrupt is a low priority interrupt.
1 = The watchdog interrupt is a high priority interrupt.
PX5
Bit 3
External Interrupt 5 Priority. This bit controls the priority of external interrupt
5.
0 = External interrupt 5 is a low priority interrupt.
1 = External interrupt 5 is a high priority interrupt.
PX4
Bit 2
External Interrupt 4 Priority. This bit controls the priority of external interrupt
4.
0 = External interrupt 4 is a low priority interrupt.
1 = External interrupt 4 is a high priority interrupt.
PX3
Bit 1
External Interrupt 3 Priority. This bit controls the priority of external interrupt
3.
0 = External interrupt 3 is a low priority interrupt.
1 = External interrupt 3 is a high priority interrupt.
PX2
Bit 0
External Interrupt 2 Priority. This bit controls the priority of external interrupt
2.
0 = External interrupt 2 is a low priority interrupt.
1 = External interrupt 2 is a high priority interrupt.
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Real Time Clock Control Register (RTCC)
SFR F9h
7
6
5
4
3
2
1
0
SSCE
SCE
MCE
HCE
RTCRE
RTCWE
RTCIF
RTCE
RW-*
SSCE
Bit 7
RW-*
RW-*
RW-*
RW*-0
RT*-0
R*-*
RT-*
R=Unrestricted Read, W=Unrestricted Write, T=Timed Access Write Only,
-n =Value after Reset, * = See Description
RTC Subsecond Register Compare Enable. This bit enables a match Bit 7
between the Real Time Alarm Subsecond Register (RTASS;F2h) and the Real
Time Clock Subsecond Register (RTCSS;FAh) to contribute to the RTC
interrupt request. This bit will be indeterminate following a no-battery reset,
and is unaffected by all other resets.
0 = The subsecond value is a Don’t Care when evaluating the RTC alarm. If
any other alarm register compare bits are enabled, this will cause one interrupt
per subsecond tick (1/256 second) for as long as the other registers match.
1 = Include the subseconds along with any other registers when evaluating alarm
compare conditions.
SCE
Bit 6
RTC Second Register Compare Enable. This bit enables a match between the
Real Time Alarm Second Register (RTAS;F3h) and the Real Time Clock
Second Register (RTCS;FBh) to contribute to the RTC interrupt request. This
bit will be indeterminate following a no-battery reset, and is unaffected by all
other resets.
0 = The second value is a Don’t Care when evaluating an RTC alarm. If any
other alarm register compare bits are enabled, this will cause one interrupt per
second as long as the other registers match.
1 = Include the second along with any other registers when evaluating alarm
compare conditions.
MCE
Bit 5
RTC Minute Register Compare Enable. This bit enables a match between Bit
5 the Real Time Alarm Minute Register (RTAM;F4h) and the Real Time Clock
Minute Register (RTCM;FCh) to contribute to the RTC interrupt request. This
bit will be indeterminate following a no-battery reset, and is unaffected by all
other resets.
0 = The minute value is a Don’t Care when evaluating an RTC alarm. If any
other alarm register compare bits are enabled, this will cause one interrupt per
minute as long as the other registers match.
1 = Include the minute along with any other registers when evaluating alarm
compare conditions.
HCE
Bit 4
RTC Hour Register Compare Enable. This bit enables a match between the
Real Time Alarm Hour Register (RTAH;F5h) and the Real Time Clock Hour
Register (RTCH;FDh) to contribute to the RTC interrupt request. This bit will
be indeterminate following a no-battery reset, and is unaffected by all other
resets.
0 = The hour value is a Don’t Care when evaluating an RTC alarm. If any other
alarm register compare bits are enabled, this will cause one interrupt per hour for
as long as the other registers match.
1 = Include the hour along with any other registers when evaluating alarm
compare conditions.
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RTCRE
Bit 3
RTC Read Enable. This bit temporarily halts internal updating of the RTC to
allow software to read the current time. No loss of time will occur. This bit will
be cleared to 0 following any reset. Attempts to set the RTCRE and RTCWE
bits simultaneously will be ignored. When this bit is cleared, software must wait
4 machine cycles before setting either the RTCRE or RTCWE bit again.
0 = Reads of the RTC clock registers (RTCSS;FAh, RTCS;FBh, RTCM;FCh,
RTCH;FDh, RTCD0;FEh, RTCD1;FFh) are prohibited and will return erroneous
values.
1 = Reads of the RTC clock registers are permitted during a 1 ms window
starting from the time the bit is set. Immediately after setting this bit, software
must wait 4 machine cycles to allow all time registers to synchronize. This bit
should be cleared by the user when the desired reads are complete, although it
will clear automatically within 1.95 ms if not cleared in software.
RTCWE
Bit 2
RTC Write Enable. This bit temporarily halts the RTC to allow software to
update the current time. No loss of time will occur. This bit can only be
modified using a Timed Access procedure. Changing this bit from 1 to 0 will
reset the RTCSS register to 00h.This bit will be cleared to 0 following any reset.
0 = Writes to the RTC clock registers (RTCSS;FAh, RTCS;FBh, RTCM;FCh,
RTCH;FDh, RTCD0;FEh, RTCD1;FFh) are ignored. Attempts to set the
RTCRE and RTCWE bits simultaneously will be ignored. When this bit is
cleared, software must wait 4 machine cycles before setting either the RTCRE
or RTCWE bit again.
1 = Writes to the RTC clock registers are permitted during a 1 ms window
starting from the time this bit is set. Immediately after setting this bit, software
must wait 4 machine cycles to allow all time registers to synchronize. This bit
should be cleared by the user when the desired updates are complete, although it
will clear automatically after 1.95 ms if not cleared in software.
RTCIF
Bit 1
RTC Interrupt Flag. This bit indicates that a RTC alarm match has been made
between all the enabled alarm registers and their corresponding clock registers.
This bit will generate an RTC Interrupt if the ERTCI bit (EIE.5) is set, and must
be cleared by software following an interrupt. RTC interrupts cannot be
generated by setting this bit. Clearing all alarm compare enable bits (RTCC.7-4)
will also clear this bit. This bit will be indeterminate following a no–battery
reset, and is unaffected by all other resets. This bit cannot be set in software.
0 = No RTC interrupts are pending.
1 = RTC Interrupt is pending/active.
RTCE
Bit 0
RTC Enable. This bit enables/disables the RTC oscillator, halting the RTC.
This bit must be accessed using a Timed Access procedure. This bit will be
indeterminate following a no-battery reset, and is unaffected by all other resets.
If RTC operation is desired, it must be enabled following battery application.
0 = RTC oscillator is disabled.
1 = RTC oscillator is enabled.
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Real Time Clock Subsecond Register (RTCSS)
7
SFR FAh RTCSS.7
R*-*
6
5
4
3
2
1
0
RTCSS.6
RTCSS.5
RTCSS.4
RTCSS.3
RTCSS.2
RTCSS.1
RTCSS.0
R*-*
R*-*
R*-*
R*-*
R*-*
R*-*
R*-*
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset, *=See Description
Real Time Clock Subseconds. This register represents the subsecond value of
the RTC. It can be read only when the RTCRE bit is set, and writes are not
permitted. It is reset to 00h when the RTCWE bit is cleared. The register counts
from 0h to FFh.
RTCSS.7-0
Bits 7-0
Real Time Clock Second Register (RTCS)
SFR FBh
7
6
5
4
3
2
1
0
0
0
RTCS.5
RTCS.4
RTCS.3
RTCS.2
RTCS.1
RTCS.0
R*-0
R*-0
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset, *=See Description
Bits 7-6
Reserved. These bits will be 0 when read.
RTCS.5-0
Bits 5-0
Real Time Clock Seconds. This register represents the second value of the
RTC. This register can be read only when the RTCRE bit is set, and can only be
modified when the RTWE bit is set. Consult the description of the RTCWE bit
for the programming protocol for this register. This register counts from 0h to
3Bh (0 to 59 seconds), and any writes to this register out-side of that range will
generate an inaccurate count.
Real Time Clock Minute Register (RTCM)
SFR FCh
7
6
5
4
3
2
1
0
0
0
RTCM.5
RTCM.4
RTCM.3
RTCM.2
RTCM.1
RTCM.0
R*-0
R*-0
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset, * = See Description
Bits 7-6
RTCM.5-0
Bits 5-0
Reserved. These bits will be 0 when read.
Real Time Clock Minutes. This register represents the minute value of the
RTC. This register can be read only when the RTCRE bit is set, and can only be
modified when the RTCWE bit is set. Consult the description of the RTCWE bit
for the programming protocol for this register. This register counts from 0h to
3Bh (0 to 59 minutes), and any writes to this register out-side of that range will
generate an inaccurate count.
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Real Time Clock Hour Register (RTCH)
7
6
5
4
3
2
1
0
DOW2
DOW1
DOW0
RTCH.4
RTCH.3
RTCH.2
RTCH.1
RTCH.0
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
SFR FDh
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset, *=See Description
DOW.2-0
Bits 7-5
Real Time Clock Day of the Week. These bits represent the current day of the
week. This register can be read only when the RTCRE bit is set, and can only be
modified when the RTCWE bit is set. Consult the description of the RTCWE bit
for the programming protocol for this register. This register counts from 1h to
7h, and increments when the hour value of the RTC (RTCH.4-0) rolls over from
17h to 0h. Writing a 0h to these bits will disable the day of week function and
the count will remain 0. No alarm corresponds to these bits.
RTCH.4-0
Bits 4-0
Real Time Clock Hours. These bits represent the hour value of the RTC. This
register can be read only when the RTCRE bit is set, and can only be modified
when the RTCWE bit is set. Consult the description of the RTCWE bit for the
programming protocol for this register. This register counts from 0h to 17h (0 to
23 hours), and any writes outside of that range will generate an inaccurate count.
Real Time Clock Day Register 0 (RTCD0)
SFR FEh
7
6
5
4
3
2
1
0
RTCD0.7
RTCD0.6
RTCD0.5
RTCD0.4
RTCD0.3
RTCD0.2
RTCD0.1
RTCD0.0
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset, *=See Description
RTCD0.7-0
Bits 7-0
Real Time Clock Day Register 0. This register contains the least significant
byte of the 16-bit current day count. This is not an absolute value tied to a
specific calendar date, but rather a relative day count defined by the user. This
register can be read only when the RTCRE bit is set, and can only be modified
when the RTCWE bit is set. Consult the description of the RTCWE bit for the
programming protocol for this register. The register counts from 0h to FFh. No
alarm corresponds to these bits.
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Real Time Clock Day Register 1 (RTCD1)
SFR FFh
7
6
5
4
3
2
1
0
RTCD1.7
RTCD1.6
RTCD1.5
RTCD1.4
RTCD1.3
RTCD1.2
RTCD1.1
RTCD1.0
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R*W*-*
R=Unrestricted Read, W=Unrestricted Write, -n=Value after Reset
RTCD1.7-0
Bits 7-0
Real Time Clock Day Register 1. This register contains the most significant
byte of the 16-bit current day count. This is not an absolute value tied to a
specific calendar date, but rather a relative day count defined by the user. This
register can be read only when the RTCRE bit is set, and can only be modified
when the RTCWE bit is set. Consult the description of the RTCWE bit for the
programming protocol for this register. The register counts from 0h to FFh. A
rollover of this register will clear RTCD1 and RTCD0. No alarm corresponds to
these bits.
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INSTRUCTION TIMING
All instructions in the High-Speed Microcontroller perform the same functions as their 80C32
counterparts. Their effect on bits, flags, and other status functions is identical. However, the timing of
each instruction is different. This applies both in absolute terms of nanoseconds for a given crystal, and
in relative terms of clocks. For absolute timing of real-time events, the timing of software loops will need
to be calculated using the data provided in Section 16, Instruction Set Details. However, timers default to
run at the older 12 clocks per timer increment and timer-based events need no modification.
The relative time of two instructions might be different in the new architecture than it was previously. For
example, both the one-byte, two-cycle “MOVX A, @DPTR” instruction and the three-byte, two-cycle
“MOV direct, direct” instruction used two cycles. In the High-Speed Microcontroller, the MOVX
instruction uses two cycles but the “MOV direct, direct” uses three cycles. While both are faster than their
original counterparts, they now have different execution times from each other because the High-Speed
Microcontroller typically uses one cycle for each byte. This is generally true for all instructions except for
MUL, DIV, MOVC, MOVX, and branch type instructions. The timing of each instruction should be
examined for familiarity with the changes. Note that a machine cycle now requires just four clocks, and
provides one ALE pulse per cycle. Many instructions require only one cycle, but some require five. In the
original architecture, all were one or two cycles except for MUL and DIV.
ADDRESSING MODES
The High-Speed Microcontroller uses the standard 8051 instruction set which is supported by a wide
range of third party assemblers and compilers. Like the 8051, the High-Speed Microcontroller uses three
memory areas. These are program memory, data memory, and Registers. Both the program and data areas
are 64KB each. They extend from 0000h to FFFFh. The register areas are located between 00h and FFh,
but do not overlap with the program and data segments. This is because the High-Speed Microcontroller
uses different modes of addressing to reach each memory segment. These modes are described below.
Program memory is the area from which all instructions are fetched. It is inherently read only. This is
because the 8051 instruction set provides no instructions that write to this area. Read/write access is for
data memory and Registers only. No special action is required to fetch from program memory. Each
instruction fetch will be performed automatically by the on-chip hardware. In versions that contain on
chip memory, the hardware will decide whether the fetch is on-chip or off-chip based on the address.
Explicit addressing modes are needed for the data memory and register areas. These modes determine
which register area is accessed or if off-chip data memory is used.
The High-Speed Microcontroller supports eight addressing modes. They are:
Register Addressing
Direct Addressing
Register Indirect Addressing
Immediate Addressing
Register Indirect Addressing with Displacement
Relative Addressing
Page Addressing
Extended Addressing
Five of the eight are used to address operands. The remainder are used for program control and
branching. When writing assembly language instructions that use arguments, the convention is
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destination, source. Each mode of addressing is summarized below. Note that many instructions (such as
ADD) have multiple addressing modes available.
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Register Addressing
Register Addressing is used for operands that are located in one of the eight Working Registers (R7-R0).
These are the currently selected Working Register bank, which reside in the lower 32 bytes of Scratchpad
RAM. A register bank is selected using two bits in the Program Status Word (PSW;D0h). This
addressing mode is powerful, since it uses the active bank without knowing which bank is selected. Thus
one instruction can have multiple uses by simply switching banks. Register Addressing is also a highspeed instruction, requiring only one machine cycle. Two examples of Register Addressing are provided
below.
ADD
INC
A, R4
R2
;Add Accumulator to register R4
;Increment the value in register R2
In the first case, the value in R4 is the source of the operation. In the later, R2 is the destination. These
instructions do not consider the absolute address of the register. They will act on whichever bank has
been selected.
Any Working Register may also be accessed by Direct Addressing, described below. To do this, the
absolute address must be specified.
Direct Addressing
Direct Addressing is the mode used to access the entire lower 128 bytes of Scratchpad RAM and the SFR
area. It is commonly used to move the value in one register to another. Two examples are shown below.
MOV
72h, 74h
MOV
90h, 20h
;Move the value in register 74 to
;register 72.
;Move the value in register 20 to
;the SFR at 90h (Port 1)
Note that there is no instruction difference between a RAM access and an SFR access. The SFRs are
simply register locations above 7Fh.
Direct Addressing also extends to bit addressing. There is a group of instructions that explicitly use bits.
The address information provided to such an instruction is the bit location, rather than the register
address. Registers between 20h and 2Fh contain bits that are individually addressable. SFRs that end in
0 or 8 are bit addressable. An example of Direct Bit Addressing is as follows.
SETB
00h
;Set bit 00 in the RAM. This is the
;LSb of the register at address 20h
;as shown in Section 4.
MOV
C, 0B7h
;Move the contents of bit B7 to the
;Carry flag. Bit B7 is the MSb of
;register B0 (Port 3).
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Register Indirect Addressing
This mode is used to access the Scratchpad RAM locations above 7Fh. It can also be used to reach the
lower RAM (0h - 7Fh) if needed. The address is supplied by the contents of the Working Register
specified in the instruction. Thus one instruction can be used to reach many values by altering the
contents of the designated Working Register. Note that in general, only R0 and R1 can be used as
pointers. An example of Register Indirect Addressing is as follows.
ANL
A, @R0
;Logical AND the Accumulator
;with the contents of the register
;pointed to by the value stored in R0.
This mode is also used for Stack manipulation. This is because all Stack references are directed by the
value in the Stack Pointer register. The Push and Pop instructions use this method of addressing. An
example is as follows.
PUSH
A
;Saves the contents of the
;accumulator on the stack.
Register Indirect Addressing is used for all off-chip data memory accesses. These involve the MOVX
instruction. The pointer registers can be R0, R1, DPTR0 and DPTR1. Both R0 and R1 reside in the
Working Register area of the Scratchpad RAM. They can be used to reference a 256 byte area of off-chip
data memory. When using this type of addressing, the upper address byte is supplied by the value in the
Port 2 latch. This value must be selected by software prior to the MOVX instruction. An example is as
follows.
MOVX
@R0, A
;Write the value in the accumulator
;to the address pointed to by R0 in
;the page pointed to by P2.
The 16-bit Data pointers (DPTRs) can be used as an absolute off-chip reference. This gives access to the
entire 64KB data memory map. An example is as follows.
MOVX
@DPTR, A
;Write the value in the accumulator
;to the address referenced by the
;selected data pointer.
Immediate Addressing
Immediate Addressing is used when one of the operands is predetermined and coded into the software.
This mode is commonly used to initialize SFRs and to mask particular bits without affecting others. An
example is as follows.
ORL
A, #40h
;Logical OR the Accumulator with 40h.
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Register Indirect with Displacement
Register Indirect Addressing with Displacement is used to access data in lookup tables in program
memory space. The location is created using a base address with an index. The base address can be
either the PC or the DPTR. The index is the accumulator. The result is stored in the accumulator. An
example is as follows.
MOVC
A, @A +DPTR
;Load the accumulator with the contents
of program memory
;pointed to by the contents of the DPTR
plus the value in
;the accumulator.
Relative Addressing
Relative Addressing is used to determine a destination address for Conditional branch. Each of these
instructions includes an 8-bit value that contains a two’s complement address offset (–127 to +128) which
is added to the PC to determine the destination address. This destination is branched to when the tested
condition is true. The PC points to the program memory location immediately following the branch
instruction when the offset is added. If the tested condition is not true, the next instruction is performed.
An example is as follows.
JZ
$–20
;Branch to the location (PC+2)–20
;if the contents of the accumulator = 0.
Page Addressing
Page Addressing is used by the Branching instructions to specify a destination address within the same
2KB block as the next contiguous instruction. The full 16-bit address is calculated by taking the five
highest order bits for the next instruction (PC+2) and concatenating them with the lowest order 11 bit
field contained in the current instruction. An example is as follows.
0870h
ACALL100h ;Call to the subroutine at address 100h
plus the
;current page address.
In this example, the current page address is 800h, so the destination address is 900h.
Extended Addressing
Extended Addressing is used by the Branching instructions to specify a 16-bit destination address within
the 64KB address space. The destination address is fixed in software as an absolute value. An example
is as follows.
LJMP
0F732h
;Jump to address 0F732h.
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PROGRAM STATUS FLAGS
All Program Status Flags are contained in the Program Status Word at SFR location D0h. It contains
flags that reflect the status of the CPU and the result of selected operations. The flags are summarized
below. The following table shows the instructions that affect each flag.
Bit Description :
PSW.7
Carry
C
Set when the previous operation resulted in a carry (during addition) or a
borrow (during subtraction), otherwise cleared.
PSW.6
Auxiliary Carry
AC
Set when the previous operation resulted in a carry (during addition) or a
borrow (during subtraction) from the high order nibble. Otherwise cleared.
PSW.2
Overflow
OV
Set when a carry was generated into the high order bit but not a carry out of
the high order bit. OV is normally used with 2’s complement arithmetic.
PSW.0
Parity
P
Set to logic 1 to indicate an odd number of ones in the accumulator (odd
parity). Cleared for an even number of ones. This produces even parity.
All of these bits are cleared to a logic 0 for all resets.
INSTRUCTIONS THAT AFFECT FLAG SETTINGS Table 4-4
INSTRUCTION
C
FLAGS
OV
INSTRUCTION
AC
C
ADD
X
X
X
CLR C
0
ADDC
X
X
X
CPL C
X
SUBB
X
X
X
ANL C, bit
X
MUL
0
X
X
DIV
0
X
ANL C, bit
ORL C, bit
DA
X
X
RRC
X
ORL C, bit
MOV C, bit
RLC
X
CJNE
X
SETB C
1
X indicates the modification is according to the result of the instruction.
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X
FLAGS
OV
AC
High-Speed Microcontroller User’s Guide
SECTION 5: CPU TIMING
The timing of the High-Speed Microcontroller is the area with the greatest departure from the original
8051 series. This section will briefly explain the timing and also compare it to the original.
OSCILLATOR
The High-Speed Microcontroller provides an on-chip oscillator circuit that can be driven by an external
crystal or by an off-chip TTL clock source. The oscillator circuit provides the internal clocking signals to
the on-chip CPU and I/O circuits.
Figure 5-1 shows the required connections for a crystal. In most cases, a crystal will be the preferred
clock source. For very low power applications, a low frequency ceramic resonator may also be used.
The capacitors shown in Figure 5-1 are typical values. If a resonator is used, higher capacitance, such as
47 pF may be needed.
For higher frequency designs, an off-chip clock oscillator may be preferred. This is illustrated in Figure
5-2. When using an off-chip oscillator, the duty cycle becomes important. As nearly as possible, a 50%
duty cycle should be supplied.
XTAL1
This pin is the input to an inverting high gain amplifier. It also serves as the input for an off-chip
oscillator. Note that when using an off-chip oscillator, XTAL2 is left unconnected.
XTAL2
This pin is the output of the crystal amplifier. It can be used to distribute the clock to other devices on the
same board. If using a crystal, the loading on this pin should be kept to a minimum, especially capacitive
loading.
OSCILLATOR CHARACTERISTICS
The High-Speed Microcontroller was designed to operate with a parallel resonant AT cut crystal. The
crystal should resonate at the desired frequency in its primary or fundamental mode. The oscillator
employs a high gain amplifier to assure a clean waveform at high frequency. Due to the high
performance nature of the product, both clock edges are used for internal timing. Therefore, the duty
cycle of the clock source is of importance. A crystal circuit will balance itself automatically. Thus
crystal users will not need to take extra precautions concerning duty cycle.
CRYSTAL SELECTION
The High-Speed Microcontroller family was designed to operate with fundamental mode crystals for
improved stability. Although most high speed (i.e., greater than 25 MHz) crystals operate from their third
overtone, fundamental mode crystals are available from most major crystal suppliers. Designers are
cautioned to ensure that high-speed crystals being specified for use in their application do operate at the
rated frequency in their fundamental mode. The use of a third overtone crystal will typically result in
oscillation rates at one-third the desired speed.
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CRYSTAL CONNECTION Figure 5-1
HIGH SPEED
MICROCONTROLLER
XTAL1
TO INTERNAL
CIRCUITS
XTAL2
33 pF
33 pF
CLOCK SOURCE INPUT Figure 5-2
HIGH SPEED MICRO
CLOCK
OSCILLATOR
XTAL1
TO INTERNAL
CIRCUITS
XTAL2
INSTRUCTION TIMING
The clock source, whether crystal or oscillator, supplies the internal functions with a precise time base.
The clock is used to create the basic unit of timing called a machine cycle. One machine cycle consists of
four clocks when operating in divide by 4 mode. The use of Power Management modes will cause the
device to utilize 64 or 1024 external clock cycles per machine cycle. Within a machine cycle there are
four states called C1, C2, C3, and C4. Various operations take place during each C state. Within this
section and throughout others, an event timing will be identified by its C state. For example, ALE rises at
the beginning of the C1 time. Since the clock source is the source of nearly all timing, the electrical
specifications are given in terms of clocks. The time of a clock period is referred to as tCLCL.
Most times in the electrical specifications are specified as some number of clocks from the edge of a
signal. The signal edges were also derived from the clock source and the C states.
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Due to the limited number of edges within a machine cycle, selected events must occur between edges.
The High-Speed Microcontroller employs sophisticated circuits to create half and quarter clock events.
That is, some events occur between clock edges. Such circuits assure that events occur as precisely as if a
clock edge were available. While being generally transparent to the user, these circuits result in the use of
fractional clocks in the electrical specifications. For example, a time may be specified as 2.5 tCLCL.
As mentioned above, a machine cycle is the basic timing unit of most functions in the High-Speed
Microcontroller. A machine cycle of the High-Speed Microcontroller is the time required to execute a
single cycle instruction. Almost half the opcodes of the 8051 instruction set are implemented in a single
machine cycle in the High-Speed Microcontroller. The remaining instructions require multiple machine
cycles.
The Power Management Modes implemented on some devices modify the number of clock cycles needed
to execute an instruction. Instead of 4 clocks per machine cycle, power management mode 1 (PMM1)
and power management mode 2 (PMM2) utilize 64 and 1024 clocks per cycle respectively to conserve
power. A full description of the power management modes and their effect on CPU operation is provided
in Section 7.
All instructions are coded within an 8-bit field called an opcode. This single byte must be fetched from
program memory. The opcode is decoded by the CPU. It determines what action the microcontroller will
take and whether more information is needed from memory. If no other memory is needed, then only one
byte was required. Thus the instruction is called a one byte instruction. In some cases, more data is
needed. These will be two or three byte instructions.
In most cases, the number of memory accesses (bytes) needed by an instruction is equal to the number of
machine cycles. Thus single cycle instructions contain one byte, and two cycle instructions have two
bytes. This is true except for the special cases mentioned below.
SINGLE CYCLE INSTRUCTIONS
The standard single cycle instruction timing is shown in Figure 5-3. As mentioned above, there are 126
opcodes that are single cycle instructions. An example of a single cycle instruction is as follows:
DEC
A
14h
TWO CYCLE INSTRUCTIONS
All two cycle instructions require two cycles because they involve two bytes or require two memory
accesses. The first byte is an opcode that instructs the CPU. This is the instruction itself. The second
byte is normally an operand or it specifies the location of the operand. For example, the instruction
“ANL A, direct” uses two cycles and requires two bytes. Two examples are as follows:
ANL A, direct
55h
a7-0
ANL A, #data
54h
d7-d0
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Note that in the first example, the first memory access is the opcode. The second memory access is the
location of the operand in the register map. Since the result is stored in an internal register, this operation
does not require a memory access. The second example is very similar. Again, the first byte represents
the opcode. In this example, the second byte is the operand itself. This byte is used directly by the
instruction. The timing for a two cycle instruction is shown in Figure 5-4.
One other type of two cycle instruction requires two cycles but only includes one byte. This is because
the second memory access is the result of the instruction. These are the MOVX instructions. An example
is as follows:
MOVX
@DPTR,A
F0h
The second cycle in this instruction is the write to data memory at the address pointed to by the data
pointer. Thus this instruction is a two cycle one byte instruction, but requires two memory accesses. The
MOVX timing is a special case, since the user can control it with the Stretch MOVX feature. The timing
for the Stretch MOVX is discussed in the section on Memory Access.
SINGLE CYCLE INSTRUCTION TIMING Figure 5-3
SINGLE CYCLE
C1
C3
C2
C4
CLK
ALE
PSEN
RETURN DATA
D7-0
AD0-7
PORT2
ADDRESS A15-A8
*Shaded areas are held in a weak latch on the port until overdriven.
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High-Speed Microcontroller User’s Guide
TWO CYCLE INSTRUCTION TIMING Figure 5-4
Example: ANL A, direct:
55h addr7-0
OPERAND
FETCH
INSTRUCTION
FETCH
C1
C3
C2
C4
C1
C3
C2
C4
CLK
ALE
PSEN
AD0POR
A7-0
PIC
RETURN
DATA
A7-0
PC+1
ADDRESS
A15-A8
RETURN DATA OPER
AND ADDRESS 7-0
ADDRESS
A15-A8
*Shaded areas are held in a weak latch on the port until overdriven.
THREE CYCLE INSTRUCTIONS
Three cycle instructions come in two varieties. The first requires three memory accesses. These are
similar to one and two cycle instructions in that the number of bytes equals the number of cycles.
The second variety is a three cycle instruction that simply requires 12 clocks to perform the function.
This may have one or two bytes. Examples of both types are shown below.
ANL direct, #data
53h
a 7–a 0
d7–d0
(3 bytes)
SJMP rel
80h
a 7–a 0
(2 bytes)
INC DPTR
A3h
(1 byte)
In the first example, the first memory fetch is the opcode. The second is the location of the destination
register. The third memory fetch is the operand that is used by the instruction. This instruction has three
memory accesses, so it requires three machine cycles. The second example has the operand in the first
byte and the jump location in the second. It requires three cycles to actually perform the jump. The third
example contains simply the opcode, which is one byte. This instruction involves the manipulation of a
16-bit register so it takes longer than 8-bit operations. Figure 5-5 shows the timing of all three types of
three cycle instructions.
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FOUR CYCLE INSTRUCTIONS
All four cycle instructions require more time than the associated number of bytes. These are all program
branching instructions that can move program control to a new location. The four cycle instructions use
either 1 or 3 bytes as shown in the following examples. Figure 5-6 shows the timing of both four cycle
instructions.
22h
RET
CJNE
B4h
d7-d0
A, #data, addr
a7-a0
FIVE CYCLE INSTRUCTIONS
There are only two 5 cycle instructions in the High-Speed Microcontroller. They are the Multiply (MUL)
and Divide (DIV). These are shown below. Figure 5-7 shows the timing of 5 cycle instructions.
MUL A, B
DIV A, B
A4h
84h
Note that the five cycle instructions require only one byte. They need 5 cycles to accomplish the math
function.
THREE CYCLE INSTRUCTION TIMING Figure 5-5
Example 1: ANL direct, #data
53h a7–a0 d7–d0
PSEN
Example 2: SJMP rel
80h a7–a0
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High-Speed Microcontroller User’s Guide
PSEN
Example 3: INC DPTR
A3h
PSEN
*Shaded areas are held in a weak latch on the port until overdriven.
FOUR CYCLE INSTRUCTION TIMING Figure 5–6
Example 1: CJNE A, #data, addr
B4h d7–d0 a7–a0
PSEN
Example 2: RET
22h
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High-Speed Microcontroller User’s Guide
PSEN
FIVE CYCLE INSTRUCTION TIMING Figure 5–7
Example: MUL A,B
A4h
PSEN
*Shaded areas are held in a weak latch on the port until overdriven.
COMPARISON TO THE 8051
The original 8051 had a 12 clock architecture. A machine cycle needed 12 clocks and most instructions
were either one or two machine cycles. Thus except for the MUL and DIV instructions, the 8051 used
either 12 or 24 clocks for each instruction. Furthermore, each cycle in the 8051 used two memory
fetches. In many cases the second fetch was a dummy, and the extra clock cycles were wasted.
The High-Speed Microcontroller uses 4 clocks per cycle. Since a cycle is now aligned with a memory
fetch when possible, most instructions have the same number of cycles as bytes. This leads to more
“categories” than the original 8051. Where there were primarily one and two cycle instructions before,
there are now one, two, three, and four cycle instructions. Multiply and Divide require five cycles. Note
however, that regardless of the number of cycles, each instruction is at least 1.5 and most are 2 to 3 times
faster than its original counterpart. Table 5-1 shows each instruction, the number of clocks used in the
High-Speed Microcontroller and the number used in the 8051 for comparison. The factor by which the
High-Speed Microcontroller improves on the 8051 is shown as the Speed Advantage. A Speed
Advantage of 3.0 means that the High-Speed Microcontroller performs the same instruction three times
faster that the 8051.
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Table 5-2 provides a summary by instruction type. Note that many of the instructions provide multiple
opcodes. As an example, the ADD A, Rn instruction can act on one of 8 working registers. There are 8
opcodes for this instruction because it can be used on 8 independent locations. Table 5-2 shows totals for
both number of instructions and number of opcodes. Averages are provided in the tables. However, the
real speed improvement seen in any system will depend on the instruction mix. Programs that use
immediate or direct data combined with the accumulator or working registers will be improved the least.
These are two cycle, two byte instructions. Moderate performance improvement will be gained by
emphasizing short branches and instructions that use only direct and immediate data (no accumulator or
working register). These instructions tend to be three cycle instructions. The largest number of
improvements come from the single cycle instructions involving only the accumulator and working
registers. Also, the two cycle data movement instructions involving the working registers are greatly
improved.
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INSTRUCTION TIMING COMPARISON Table 5-1
High–Speed Microcontroller is abbreviated as HSM.
HSM
HSM
HEX
CLOCK
TIME
INSTRUCTION
CODE
CYCLES
@ 25 MHz
ADD A, Rn
28..2F
4
160 ns
ADD A, direct
25
8
320 ns
ADD A, @Ri
26..27
4
160 ns
ADD A, #data
24
8
320 ns
ADDC A, Rn
38..3F
4
160 ns
ADDC A, direct
35
8
320 ns
ADDC A, @Ri
36..37
4
160 ns
ADDC A, #data
34
8
320 ns
SUBB A, Rn
98..9F
4
160 ns
SUBB A, direct
95
8
320 ns
SUBB A, @Ri
96..97
4
160 ns
SUBB A, #data
94
8
320 ns
INC A
04
4
160 ns
INC Rn
08..0F
4
160 ns
INC direct
05
8
320 ns
INC @Ri
06..07
4
160 ns
INC DPTR
A3
12
480 ns
DEC A
14
4
160 ns
DEC Rn
18..1F
4
160 ns
DEC direct
15
8
320 ns
DEC @Ri
16..17
4
160 ns
MUL AB
A4
20
800 ns
DIV AB
84
20
800 ns
DA A
D4
4
160 ns
ANL A, Rn
58..5F
4
160 ns
ANL A, direct
55
8
320 ns
ANL A, @Ri
56..57
4
160 ns
ANL A, #data
54
8
320 ns
ANL direct, A
52
8
320 ns
ANL direct, #data
53
12
480 ns
ORL A, Rn
48..4F
4
160 ns
ORL A, direct
45
8
320 ns
ORL A, @Ri
46..47
4
160 ns
ORL A, #data
44
8
320 ns
ORL direct, A
42
8
320 ns
ORL direct, #data
43
12
480 ns
XRL A, Rn
68..6F
4
160 ns
XRL A, direct
65
8
320 ns
XRL A, @Ri
66..67
4
160 ns
XRL A, #data
64
8
320 ns
XRL direct, A
62
8
320 ns
XRL direct, #data
63
12
480 ns
CLR A
E4
4
160 ns
CPL A
F4
4
160 ns
RL A
23
4
160 ns
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8051
CLOCK
CYCLES
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
24
12
12
12
12
48
48
12
12
12
12
12
12
24
12
12
12
12
12
24
12
12
12
12
12
24
12
12
12
8051
TIME
@ 25 MHz
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
960 ns
480 ns
480 ns
480 ns
480 ns
1.92 us
1.92 us
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
960 ns
480 ns
480 ns
480 ns
480 ns
480 ns
960 ns
480 ns
480 ns
480 ns
480 ns
480 ns
960 ns
480 ns
480 ns
480 ns
HSM vs. 8051
SPEED
ADVANTAGE
3
1.5
3
1.5
3
1.5
3
1.5
3
1.5
3
1.5
3
3
1.5
3
2
3
3
1.5
3
2.4
2.4
3
3
1.5
3
1.5
1.5
2
3
1.5
3
1.5
1.5
2
3
1.5
3
1.5
1.5
2
3
3
3
High-Speed Microcontroller User’s Guide
RLC A
RR A
RRC A
SWAP A
MOV A, Rn
MOV A, direct
MOV A, @Ri
MOV A, #data
MOV Rn, A
MOV Rn, direct
MOV Rn, #data
MOV direct, A
MOV direct, Rn
MOV direct, direct
MOV direct, @Ri
MOV direct, #data
MOV @Ri, A
MOV @Ri, direct
MOV @Ri, #data
MOV DPTR, #data 16
MOVC A, @A+DPTR
MOVC A, @A+PC
MOVX A, @Ri
MOVX A, @DPTR
MOVX @Ri, A
MOVX @DPTR, A
PUSH direct
POP direct
XCH A, Rn
XCH A, direct
XCH A, @Ri
XCHD A, @Ri
CLR C
CLR bit
SETB C
SETB bit
CPL C
CPL bit
ANL C, bit
ANL C, bit
ORL C, bit
ORL C, bit
MOV C, bit
MOV bit, C
ACALL addr 11
Hex codes=11, 31, 51,
71, 91, B1, D1, or F1
LCALL addr 16
RET
33
03
13
C4
E8..EF
E5
E6..E7
74
F8..FF
A8..AF
78..7F
F5
88..8F
85
86..87
75
F6..F7
A6..A7
76..77
90
93
83
E2..E3
E0
F2..F3
F0
C0
D0
C8..CF
C5
C6..C7
D6..D7
C3
C2
D3
D2
B3
B2
82
B0
2
A0
A2
92
Hex code
Byte 1
4
4
4
4
4
8
4
8
4
8
8
8
8
12
8
12
4
8
8
12
12
12
8
8
8
8
8
8
4
8
4
4
4
8
4
8
4
8
8
8
8
8
8
8
160 ns
160 ns
160 ns
160 ns
160 ns
320 ns
160 ns
320 ns
160 ns
320 ns
320 ns
320 ns
320 ns
480 ns
320 ns
480 ns
160 ns
320 ns
320 ns
480 ns
480 ns
480 ns
320 ns
320 ns
320 ns
320 ns
320 ns
320 ns
160 ns
320 ns
160 ns
160 ns
160 ns
320 ns
160 ns
320 ns
160 ns
320 ns
320 ns
320 ns
320 ns
320 ns
320 ns
320 ns
12
12
12
12
12
12
12
12
12
24
12
12
24
24
24
24
12
24
12
24
24
24
24
24
24
24
24
24
12
12
12
12
12
12
12
12
12
12
24
24
24
24
12
24
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
960 ns
480 ns
480 ns
960 ns
960 ns
960 ns
960 ns
480 ns
960 ns
480 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
960 ns
960 ns
960 ns
960 ns
480 ns
960 ns
3
3
3
3
3
1.5
3
1.5
3
3
1.5
1.5
3
2
3
2
3
3
1.5
2
2
2
3
3
3
3
3
3
3
1.5
3
3
3
1.5
3
1.5
3
1.5
3
3
3
3
1.5
3
12
480 ns
24
960 ns
2
12
22
16
16
640 ns
640 ns
24
24
960 ns
960 ns
1.5
1.5
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High-Speed Microcontroller User’s Guide
RETI
AJMP addr 11
Hex code=01, 21, 41,
61, 81, A1, C1, or E1
LJMP addr 16
JMP @A+DPTR
SJMP rel
JZ rel
JNZ rel
JC rel
JNC rel
JB bit, rel
JNB bit, rel
JBC bit, rel
CJNE A, direct, rel
CJNE A, #data, rel
CJNE Rn, #data, rel
CJNE @Ri, #data, rel
DJNZ Rn, rel
DJNZ direct, rel
NOP
32
16
Hex code
Byte 1
12
640 ns
24
960 ns
1.5
480 ns
24
960 ns
2
2
73
80
60
70
40
50
20
30
10
B5
B4
B8..BF
B6..B7
D8..DF
D5
00
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
480 ns
640 ns
640 ns
640 ns
640 ns
640 ns
640 ns
640 ns
480 ns
640 ns
160 ns
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
12
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
960 ns
480 ns
1.5
2
2
2
2
2
2
1.5
1.5
1.5
1.5
1.5
1.5
1.5
2
1.5
3
16
12
12
12
12
12
12
16
16
16
16
16
16
16
12
16
4
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INSTRUCTION SPEED SUMMARY Table 5-2
SPEED
INSTRUCTION CATEGORY
Total Instructions: One Cycle One Byte
QUANTITY
ADVANTAGE
37
3.0
Total Instructions: Two Cycle One Byte
4
3.0
Total Instructions: Two Cycle Two Bytes X1.5
27
1.5
Total Instructions: Two cycle Two Bytes X3.0
11
3.0
Total Instructions: Three Cycle One Byte
4
2.0
Total Instructions: Three Cycle Two Bytes
8
2.0
Total Instructions: Three Cycle Three Bytes
7
2.0
Total Instructions: Four Cycle One Byte
2
1.5
Total Instructions: Four Cycle Three Bytes
9
1.5
Total Instructions: Five Cycle One Byte
2
2.4
Average Across all Instructions
111
2.3
Total Opcodes: One Cycle One Byte
126
3.0
Total Opcodes: Two Cycle One Byte
6
3.0
Total Opcodes: Two Cycle Two Bytes X1.5
35
1.5
Total Opcodes: Two Cycle Two Bytes X3.0
27
3.0
Total Opcodes: Three Cycle One Byte
4
2.0
Total Opcodes: Three Cycle Two Bytes
29
2.0
Total Opcodes: Three Cycle Three Bytes
7
2.0
Total Opcodes: Four Cycle One Byte
2
1.5
Total Opcodes: Four Cycle Three Bytes
17
1.5
Total Opcodes: Five Cycle One Byte
2
2.4
255
2.5
Average Across all Instructions
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High-Speed Microcontroller User’s Guide
SECTION 6: MEMORY ACCESS
The High-Speed Microcontroller follows the memory interface convention established for the industry
standard 80C51/80C31. Products in the family may vary, so refer to the specific product data sheet for
any potential differences. Like the 8051 series, the High-Speed Microcontroller uses two memory
segments. These are program memory and data memory. Program memory is read–only and is usually
implemented in ROM or EPROM. Data memory is read/write and is commonly implemented in SRAM.
Memory areas can be implemented as either on-chip, off-chip, or a combination. When using devices
without internal program memory, or if the maximum address of on-chip program or data memory is
exceeded, the device will perform an external memory access using the Expanded memory bus on ports 0
and 2. While serving as a memory bus, port 0 and port 2 do not function as I/O ports, following the
standard 8051 convention of addressing external memory. The PSEN signal will go active low to serve
as a chip enable or output enable when performing a code fetch from external memory. Products with no
on-chip program memory such as the DS80C320 will always use the Expanded bus. These devices have
no Port 0 latch since the port is dedicated for memory operations. Devices which incorporate on-chip
MOVX data memory operate in a similar fashion, except that the RD and WR signals serve as chip
enables when accessing an external SRAM.
Program execution begins at the reset vector, address 0000h. Any reset will cause the next program fetch
to begin at this location. Subsequent branches and interrupts determine how the memory fetch deviates
from sequential addressing. Since all programs begin at 0000h, this will be the beginning address of all
program execution. If on-chip program memory is present, program execution will begin at internal
location 0000h, otherwise external program memory will be used.
INTERNAL PROGRAM MEMORY
Some members of the High-Speed Microcontroller family incorporate internal EPROM or ROM for
program storage. On-chip program memory begins at address 0000h and is contiguous through the
amount of on-chip memory. Exceeding the maximum address of on–chip memory will cause the device
to perform an external memory access using the Expanded memory bus on ports 0 and 2. For example, if
the on-chip program memory is 16KB, then it lies between 0000h and 3FFFh in a contiguous area. Thus
a fetch at program memory location 4000h would be directed to the Expanded bus. Restricting memory
operations within the on-chip memory allows ports 0 and 2 to be used for general purpose I/O. For more
information concerning memory size for a specific device, consult the specific data sheet.
The High-Speed Microcontroller family was designed to be compatible with industry standard 87C51FB
programming tools. A number of third-party device programmers are available which support Dallas
Semiconductor products. In addition, Dallas Semiconductor manufactures the DS87000 Microcontroller
Programmer, specifically designed for EPROM-based members of the High-Speed Microcontroller
family.
INTERNAL DATA MEMORY
Some members of the High-Speed Microcontroller family incorporate internal SRAM for additional data
storage. This memory is addressed via MOVX commands, and is in addition to the 256 bytes of
scratchpad memory. On-chip data memory begins at address 0000h and is contiguous through the
amount of on-chip memory. Exceeding the maximum address of on-chip memory will cause the device
to perform an external memory access using the Expanded memory bus on ports 0 and 2. For example, if
the on-chip program memory is 1KB, then it lies between 0000h and 03FFh in a contiguous area. Thus a
MOVX instruction affecting memory location 0400h would be directed to the Expanded bus.
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High-Speed Microcontroller User’s Guide
Another advantage of internal data memory is that it guarantees a 2 machine cycle data memory access.
This data can be made nonvolatile on the DS87C530 through the use of an external battery. Restricting
memory operations within the on–chip memory allows ports 0 and 2 to be used for general purpose I/O.
For more information concerning memory size for a specific device, consult the corresponding data sheet.
Upon a power-on reset, the internal data memory area is disabled and transparent to the system map. Any
memory access between 0000h and FFFFh will be directed to the Expanded bus. This allows the device
to remain drop-in compatible with existing 87C52 designs. To enable the internal SRAM area, software
must configure the Data Memory Enable bits DME1, DME0 (PMR.1-0). The three memory
configurations shown in Table 6-1 are supported to allow either external data memory access via the
expanded bus, internal data memory access, or read-only access to the EPROM System Control Byte.
Note that these bits are cleared after a reset, so access to the internal data memory is prohibited until these
bits are modified. The contents of internal data memory are not affected by the changing of the Data
Memory Enable bits.
DATA MEMORY ACCESS CONTROL Table 6-1
DME1
0
0
DME0
0
1
1
1
0
1
DATA MEMORY ADDRESS RANGE
0000h–FFFFh
0000h–03FFh
0400h–FFFFh
Reserved
0000h–03FFh
0400h–FFFBh
FFFCh
FFFDh–FFFFh
DATA MEMORY LOCATION
External Data Memory (default)
Internal Data Memory
External Data Memory
Reserved
Internal Data Memory
Reserved
System Control Byte (Read only)
Reserved
ROMSIZE FEATURE
Members of the High-Speed Microcontroller family which incorporate internal program memory allow
the system to dynamically vary the on-chip memory size. This permits the device to reconfigure the
upper limit of on-chip memory, allowing a portion of the memory to be mapped off-chip. The size of onchip memory can vary from 0KB to the full range of memory, allowing the device to behave like a device
with less on-chip memory.
This feature has two primary uses. In the first instance, it allows the device to act as a bootstrap loader
for a Flash memory or nonvolatile SRAM (NV SRAM). The internal program memory can contain a
bootstrap loader, which can program the external memory device. Secondly, this method can be used to
increase the amount of available program memory from 64KB to 80KB without bank switching.
The maximum amount of on-chip memory is selected by configuring the ROM Size Select register bits
RMS2, RMS1, RMS0 (ROMSIZE.2-0). The modification of the ROMSIZE register must be followed by
a 2 machine cycle delay, such as executing two NOP instructions, before jumping to the new address
range. Interrupts must be disabled during this operation, because a jump to the interrupt vector during the
changing of the memory map can cause erratic results. In addition, modification of the ROMSIZE
register must be done from a location that will be valid both before and after the on-chip memory
configuration. If off-chip memory access is planned, it is recommended that ports 0 and 2 not be used as
general purpose I/O, as their state will be disturbed by the memory operations. The settings for the ROM
Size Select register are shown in Table 6-2. Note that the memory configurations shown are not available
on all devices.
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High-Speed Microcontroller User’s Guide
ROMSIZE REGISTER SETTINGS Table 6-2
RMS2
0
0
0
0
1
1
1
1
RMS1
0
0
1
1
0
0
1
1
RMS0
0
1
0
1
0
1
0
1
Max. On-chip ROM
0KB
1KB
2KB
4KB
8KB
16KB
32KB
64KB
After reset, a device with internal program memory will reset the ROMSIZE bits to their default setting.
This will be the maximum amount of on-chip memory for that device. The procedure to reconfigure the
amount of on-chip memory is as follows:
1.
2.
3.
4.
5.
6.
7.
Jump to a location in program memory that will be unaffected by the change,
Disable interrupts by clearing the EA bit (IE.7),
Write AAh to the Timed Access Register (TA;C7h),
Write 55h to the Timed Access Register (TA;C7h),
Modify the ROM Size Select bits (RMS2-RMS0),
Delay 2 machine cycles (2 NOP instructions),
Enable interrupts by setting the EA bit (IE.7).
If the 0KB of internal program memory setting is selected, extra precautions must be taken. In this case,
it will be necessary to duplicate the interrupt vector table in external program memory. This is because
the interrupt vector table is located in the lower 1KB of memory, and the device will automatically
redirect any fetches from the interrupt vector table to external memory. Care must be exercised when
assembling or compiling the program so that all the modules are located at the correct starting address,
including the interrupt vector table.
PROGRAM MEMORY INTERCONNECT
The program memory interconnect scheme for the High-Speed Microcontroller family is shown in Figure
6-1. This example uses the DS80C320 and one 32K x 8 EPROM. The Program Store Enable (PSEN)
signal is used to provide an output enable to the EPROM. It can also be used to provide a chip enable,
but this produces less favorable timing. The address LSB and data are multiplexed on port 0, and the
address MSB is provided on port 2. An external latch, shown in the diagram as a 74F373, is used to latch
the lower byte of the address to the memory device. The Address Latch Enable (ALE) signal controls the
timing of the latch so that the operation is performed in the proper sequence. The signals and relative
timing for a program access are shown in Figure 6-2.
When implementing a high-speed memory interface, the F series (or faster) logic should be used. HC
logic will have worst case propagation delays that are too long. Specifications for all devices should be
checked. More information on memory interface timing can be found in Application Note 57, DS80C320
Memory Interface Timing, and Application Note 85, High Speed Microcontroller Interface Timing.
The first product in the family, the DS80C320, provides an extremely high-speed interface to external
ROM or EPROM. This assures that the user can use the slowest, and least expensive, memory device for
a given crystal speed. The DS80C320 provides very fast slew rates, but controls ringing and overshoot.
Fast slew rates allow the maximum possible time for memory access. In most cases, however, these
aspects will be transparent to the user. Refer to the electrical specifications for exact timing of each
product.
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DATA MEMORY INTERCONNECT
As described in Section 4, the High-Speed Microcontroller provides a small amount of RAM mapped as
registers for on-chip direct access. This is not considered data memory and does not fall into the memory
map. Systems that require more RAM or memory mapped peripherals must use the data memory area.
This segment is a 64KB space located between 0000h and FFFFh. It is reached using the MOVX
instruction. Any use of this instruction automatically accesses the data area. Although, the original 8051
convention placed all data memory off-chip, many members of the High-Speed Microcontroller family
contain some data memory on-chip.
From a software standpoint, the physical location of the data area is not relevant because the same
instructions are used. Like the program segment, if software accesses a data address that is above the onchip data area, this access will automatically be routed to the Expanded bus. Thus data or peripherals that
are off-chip can be used in conjunction with on-chip memory by selecting addresses that do not overlap.
As an example, if the microcontroller has 1KB of on-chip data memory, then a MOVX instruction at
location 0400h will be directed off-chip via the Expanded bus.
The physical connection of off-chip data memory is shown in Figure 6-3. This illustrates a DS80C320
with interfaced with an 8K SRAM. The data memory map begins at address 0000h since the DS80C320
has no on-chip data memory. A similar interconnection scheme would be implemented if a device with
internal data memory, such as the DS87C520 would be used. Note that any external memory that
overlapped the range of on-chip data memory would not be used.
PROGRAM MEMORY INTERFACE Figure 6-1
PSEN
ALE
OE
CK
74F373
LATCH
DS80C320
PORT 2
LBS ADDRESS
(8)
27C256
32K X 8
EPROM
DATA BUS
(8)
MSB ADDRESS
(7)
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PROGRAM MEMORY SIGNALS Figure 6-2
SINGLE CYCLE
ALE
PSEN
PORT 0
LSB
ADDR
DATA
MSB
ADDRESS
PORT 2
XTAL1
DATA MEMORY INTERFACE Figure 6-3
ALE
74F373
LATCH
LBS ADDRESS
(8)
8K X 8
SRAM
DATA BUS
(8)
MSB ADDRESS
(5)
DS80C320
RD (P3.7)
OE
WR (P3.6)
WE
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DATA MEMORY ACCESS
As mentioned above, the High-Speed Microcontroller uses the MOVX instruction for data memory
access. This includes off-chip RAM and memory mapped peripherals needing read/write access. Several
aspects of the MOVX operation have been enhanced as compared to the original 8051. The principal
improvements are in the areas of the MOVX timing and the Data Pointer.
The MOVX instruction is used to generate read/write access to off-chip address locations. It has several
addressing modes. The first uses the MOVX @ Ri command to reach a 256 byte block, This instruction
uses the value in the designated working register to address one of 256 locations. The upper byte of the
address is supplied by the value in the Port 2 latch. A second way to access data is the Data Pointer
(DPTR). This 16-bit register provides an absolute address for data memory access. 16-bits cover the
entire 64KB area. Thus the DPTR serves as a pointer to memory. Using the DPTR, the relevant
instruction is MOVX @DPTR.
The original 8051 contained one DPTR. While this provides access to the entire memory area, it is
difficult to move data from one address to another. The High-Speed Microcontroller provides two Data
Pointers. Thus software can load both a source and a destination address. The MOVX instruction will
use the active pointer to direct the off-chip address.
The Data Pointers are called DPTR0 and DPTR1. DPTR0 is located at SFR addresses 82h and 83h.
These are the locations used by the original 8051. No modification of standard code is needed to use
DPTR0. The new DPTR is located at SFR 84h and 85h. The Data Pointer Select bit (SEL) chooses the
active pointer and is located at the LSb of the SFR location 86h. No other bits in register 86h have any
effect and are set to 0. When DPS is set to 0, the DPTR0 is active. When set to 1, DPTR1 is used.
The user switches between data pointers by toggling the SEL bit. The INC instruction is the fastest way
to accomplish this. All DPTR-related instructions use the currently selected DPTR for any activity.
Therefore only one instruction is required to switch from a source to a destination address. Using the
Dual Data Pointer saves code from needing to save source and destination addresses when doing a block
move. Once loaded, the software simply switches between DPTR0 and DPTR1. Sample code listed
below illustrates the saving from using the dual DPTR. The relevant register locations are summarized as
follows.
DPL
DPH
DPL1
DPH1
DPS
82h
83h
84h
85h
86h
Low byte original DPTR
High byte original DPTR
Low byte new DPTR
High byte new DPTR
DPTR Select (LSb)
The example program listed below was original code written for an 8051 and requires a total of 1869
machine cycles on the DS80C320. This takes 299 µs to execute at 25 MHz. The new code using the Dual
DPTR requires only 1097 machine cycles taking 175.5 µs. The Dual DPTR saves 772 machine cycles or
123.5 µs for a 64 byte block move. Since each pass through the loop saves 12 machine cycles when
compared to the single DPTR approach, larger blocks gain more efficiency using this feature.
A typical application of the Dual Data Pointer is moving data from an external RAM to a memory
mapped display. Another application would be to retrieve data from a stored table, process it using a
software algorithm, then store the result in a new table.
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64 BYTE BLOCK MOVE WITH DUAL DATA POINTER
; SH and SL are high and low byte source address.
; DH and DL are high and low byte of destination address.
; DPS is the data pointer select. Reset condition DPTR0.
# CYCLES
DPS
MOV
MOV
INC
MOV
EQU 86h
R5, #64
DPTR, #DHDL
DPS
DPTR, #SHSL
MOVE:
; THIS LOOP IS PERFORMED
MOVX
A, @DPTR
INC
DPS
MOVX
@DPTR, A
INC
DPTR
INC
DPS
INC
DPTR
DJNZ
R5, MOVE
;
;
;
;
;
TELL ASSEMBLER ABOUT DPS
NUMBER OF BYTES TO MOVE
LOAD DESTINATION ADDRESS
CHANGE ACTIVE DPTR
LOAD SOURCE ADDRESS
R5 TIMES, IN THIS EXAMPLE 64
; READ SOURCE DATA BYTE
; CHANGE DPTR TO DESTINATION
; WRITE DATA TO DESTINATION
; NEXT DESTINATION ADDRESS
; CHANGE DATA POINTER TO SOURCE
; NEXT SOURCE ADDRESS
; FINISHED WITH TABLE?
2
3
2
2
2
2
2
3
2
3
3
64 BYTE BLOCK MOVE WITHOUT DUAL DATA POINTER
; SH and SL are high and low byte source address.
; DH and DL are high and low byte of destination address.
MOV
MOV
MOV
MOV
MOV
MOV
R5, #64d
DPTR, #SHSL
R1, #SL
R2, #SH
R3, #DL
R4, #DH
MOVE:
; THIS LOOP IS PERFORMED
MOVX
A, @DPTR
MOV
R1, DPL
MOV
R2, DPH
MOV
DPL, R3
MOV
DPH, R4
MOVX
@DPTR, A
INC
DPTR
MOV
R3, DPL
MOV
R4, DPH
MOV
DPL, R1
MOV
DPH, R2
INC
DPTR
DJNZ
R5, MOVE
;
;
;
;
;
;
NUMBER OF BYTES TO MOVE
LOAD SOURCE ADDRESS
SAVE LOW BYTE OF SOURCE
SAVE HIGH BYTE OF SOURCE
SAVE LOW BYTE OF DESTINATION
SAVE HIGH BYTE OF DESTINATION
R5 TIMES, IN THIS EXAMPLE 64
; READ SOURCE DATA BYTE
; SAVE NEW SOURCE POINTER
;
; LOAD NEW DESTINATION
;
; WRITE DATA TO DESTINATION
; NEXT DESTINATION ADDRESS
; SAVE NEW DESTINATION POINTER
;
; GET NEW SOURCE POINTER
;
; NEXT SOURCE ADDRESS
; FINISHED WITH TABLE?
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# CYCLES
2
3
2
2
2
2
2
2
2
2
2
2
3
2
2
2
2
3
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High-Speed Microcontroller User’s Guide
DATA MEMORY TIMING
Data memory timing refers to the execution of the MOVX instruction. This instruction includes a
program fetch memory access, then a read or write memory access. The program fetch for a MOVX
instruction is no different from any other instruction. The unique timing occurs for the second memory
operation when data is accessed.
As described in Section 5, the High-Speed Microcontroller uses four oscillator clocks for each machine
cycle. A machine cycle involves one memory access. Generally, an instruction using two memory
accesses would be a two machine cycle instruction (except for branches, MUL, DIV, INC DPTR, MOVC,
and MOVX). The MOVX instruction is unique in that the user determines the time allowed for a data
memory access. This feature is called the Stretch MOVX instruction.
The High-Speed Microcontroller allows the application software to adjust the speed of data memory
access. The microcontroller is capable of performing the MOVX in as little as two machine cycles.
Since one machine cycle is used for the program fetch, this leaves one machine cycle to perform the
actual data memory access. However, this value can be adjusted as needed so that both fast memory and
slow memory or peripherals can be accessed with no glue logic. Even in high-speed systems, it may not
be necessary to perform data memory access at full speed. In addition, there are a variety of slower
memory mapped peripherals such as LCD displays or UARTs.
When using a MOVX instruction, the user controls the time for which a read or write strobe is kept
active. Setup and hold times are also adjusted. Thus the Stretch value will be selected to provide a long
enough memory strobe to satisfy the access time of the target device.
The Stretch MOVX is controlled by a value in a special function register described below. This allows
the user to select a stretch value between zero and seven. A Stretch of zero will result in a two machine
cycle MOVX. This leaves one machine cycle to actually read or write data. A Stretch of seven will
result in a MOVX of nine cycles. The time is added to the middle of the memory strobe, creating a very
long read or write cycle. The Stretch value can be changed dynamically under software control
depending on the type of memory or peripheral to be accessed.
On reset, the Stretch value will default to a one, resulting in a three cycle MOVX. Therefore, data
memory access will not be performed at full speed. This is a convenience to existing designs that may
not have fast RAM in place. When maximum speed is desired, the software should select a Stretch value
of zero. Note that faster RAMs will be needed. When using very slow RAM or peripherals, a larger
stretch value can be selected. Note that this affects data memory only and the only way to slow program
memory (ROM) access is to use a slower crystal.
Using a Stretch value between one and seven results in a wider read/write strobe allowing more time for
memory/peripherals to respond. The microcontroller stretches the read/write strobe and all related
timing. The full speed access is shown in Figure 6-4. Note that this is not the reset default case. A three
cycle MOVX is shown in Figure 6-5A. This is the reset default condition. To modify the MOVX timing,
the Stretch value in the Clock Control register described below must be changed. Figure 6-5B shows the
timing for a four cycle MOVX (Stretch=2).
Table 6-1 below shows the resulting strobe widths for each Stretch value. The memory stretch is
implemented using the Clock Control Special Function Register at SFR location 8Eh. The stretch value is
selected using bits CKCON.2-0. In the table, these bits are referred to as M2 through M0. Note that the
Stretch time can be dynamically varied, allowing fast RAM’s but slow peripherals. The first stretch
allows the use of common 120 ns or 150 ns RAM’s without dramatically lengthening the memory access.
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High-Speed Microcontroller User’s Guide
Note that the first Stretch value does not follow the pattern of adding four clocks to the strobe. This is
because the first Stretch uses one clock to create additional set-up and one clock to create additional hold
time. Systems using a Stretch cycle of zero are presumed to be fast enough or to be running at a slower
clock speed. Since the Stretch is based on crystal timing, the resulting pulse widths must be viewed on
the basis of the real system timing.
DATA MEMORY CYCLE STRETCH VALUES Table 6-1
CKCON.2-0
M2
0
0
0
0
1
1
1
1
M1
0
0
1
1
0
0
1
1
MEMORY
CYCLES
M0
0
1
0
1
0
1
0
1
RD OR WR STROBE WIDTH
IN CLOCK
t @ 25 MHz
t @ 12 MHz
2
80 ns
167 ns
4
160 ns
333 ns
8
320 ns
667 ns
12
480 ns
1000 ns
16
640 ns
1333 ns
20
800 ns
1667 ns
24
960 ns
2000 ns
28
1120 ns
2333 ns
2
3 (default)
4
5
6
7
8
9
Note: These numbers represent nominal values. Actual timing may vary slightly.
FULL SPEED MOVX INSTRUCTION Figure 6-4
Last Cycle of
Previous
Instruction
First
Machine
Cycle
Next
Instruction
Machine
Cycle
Second
Machine
Cycle
MOVX Instruction
C1
C2
C3
C4
C1
C2
C3
C4
C1
C2
C3
C4
C1
C2
C3
C4
CLK
ALE
PSEN
WR
PORT 0
A0-A7
MOVX
Instruction
Address
PORT 2
D0-D7
A0-A7
D0-D7
Next
Instruction
MOVX
Next
Instruction Address Instruction
Read
A8-A15
A8-A15
A0-A7
D0-D7
MOVX
Data
Address
MOVX
Data
A8-A15
DATA MEMORY WRITE (2 CYCLE, STRETCH=0)
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THREE CYCLE MOVX INSTRUCTION Figure 6-5a
Last Cycle
of
Previous
Instruction
First
Machine
Cycle
Second
Machine
Cycle
Next
Instruction
Machine
Cycle
Third
Machine
Cycle
MOVX Instruction
C1 C2
C3 C4
C1 C2
C3
C4
C1 C2
C3
C4 C1
C2 C3
C4
C1
C2 C3
C4
CLK
ALE
PSEN
WR
AD0-AD7
A0-A7
D0-D7
A0-A7
Next
Instruction
Address
MOVX
Instruction
Address
MOVX
Instruction
PORT 2
D0-D7
A8-A15
A0-A7
MOVX
Data
Address
Next
Instruction
Read
A8-A15
D0-D7
MOVX
Data
A8-A15
THREE CYCLE DATA MEMORY WRITE (RESET DEFAULT)
STRETCH VALUE=1
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High-Speed Microcontroller User’s Guide
FOUR CYCLE MOVX INSTRUCTION Figure 6-5b
Last Cycle of
Previous
Instruction
First
Machine
Cycle
Second
Machine
Cycle
Third
Machine
Cycle
Fourth
Machine
Cycle
Next
Instruction
Machine
Cycle
MOVX Instruction
C1 C2
C3 C4 C1 C2
C3 C4 C1 C2
C3 C4 C1 C2
C3 C4 C1 C2
C3 C4 C1 C2
C3 C4
CLK
ALE
PSEN
WR
AD0-AD7
A0-A7
D0-D7
MOVX
Instruction
Address
A0-A7
Next
Instruction
Address
MOVX
Instruction
PORT 2
A8-A15
D0-D7
A0-A7
D0-D7
MOVX
Data
Address
D0-D7
MOVX
Data
Next
Instruction
Read
A8-A15
A0-A7
A8-A15
FOUR CYCLE DATA MEMORY WRITE
STRETCH VALUE=2
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High-Speed Microcontroller User’s Guide
SECTION 7: POWER MANAGEMENT
The High-Speed Microcontroller has several features that relate to power consumption and management.
They provide a combination of controlled operation in unreliable power applications and reduced power
consumption in portable or battery powered applications. The range of features is shown below with
details to follow.
POWER MANAGEMENT
EARLY WARNING POWER FAIL INTERRUPT
POWER FAIL/POWER ON RESET
BAND–GAP SELECT
WATCHDOG WAKE UP FROM IDLE
POWER SAVING
IDLE MODE
STOP MODE
RING WAKE UP FROM STOP
POWER MANAGEMENT MODES
PRECISION VOLTAGE MONITOR
The High-Speed Microcontroller uses a precision band-gap reference and other analog circuits to monitor
the state of the power supply during power-up and power-down transitions. Other microcontroller
systems would require external circuits to perform these functions. The band-gap reference provides a
precise voltage to compare with VCC. When VCC begins to drop, the Power Monitor compares it to its
reference. This enables the analog circuits to detect when VCC passes through predetermined thresholds,
VPFW and VRST. These are specified in the individual product data sheets.
EARLY WARNING POWER FAIL INTERRUPT
Devices which incorporate the precision voltage reference have the ability to generate a power-fail
interrupt and/or reset in response to a low supply voltage. When VCC reaches the VPFW threshold, the
microcontroller can generate an power-fail Interrupt. This early warning of supply voltage failure allows
the system time to save critical parameters in nonvolatile memory and put external functions in a safe
state.
The power-fail interrupt is optional and is enabled using the Enable Power Fail Warning Interrupt (EPFI)
bit at WDCON.5. If enabled, VCC dropping below VPFW will cause the device to vector to address 33h.
The Power-fail Interrupt status bit, PFI (WDCON.4), will be set anytime VCC transitions below VPFW.
This flag is not cleared when VCC is above VPFW, and software should clear it immediately after reading
it. As long as the condition exists, PFI will be immediately set again by hardware.
A typical application of the PFI is to place the device into a “safe mode” when a power loss appears
imminent. When the interrupt occurs, the code vectors to location 33h. At this time, software can disable
the interrupt, save any critical data, clear PFI, then continually poll the status of the power supply via the
PFI flag. As long as PFI is set, power is still below VPFW. If power returns to the proper level, PFI will
not be set once cleared by software. This indicates a safe operating condition. If power continues to fall,
a power-fail reset will be invoked automatically.
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POWER-FAIL RESET
Devices which incorporate the power-fail reset will automatically invoke a reset when VCC drops below
VRST. This will halt device operation, and place all outputs in their reset state. This state will continue to
be held until VCC drops below the voltage necessary to power the port pins. Because VRST is lower than
VPFW, the microcontroller has the option to use the power-fail interrupt to place the device into a “safe”
state before the device halts operation with a power-fail reset. This feature is automatic on devices which
incorporate the power-fail reset feature, and cannot be disabled.
POWER ON RESET
When VCC is applied to a system using the High-Speed Microcontroller, the device will hold itself in reset
until power is within tolerance and stable. An internal band-gap reference provides a highly accurate and
stable means of detecting power supply levels. It requires no external circuits to accomplish this. As
power rises, the processor will stay in a reset state until VCC > VRST. As VCC rises above VRST, internal
analog circuits will detect this and activate the on-chip crystal oscillator. On-chip hardware will then
count 65536 oscillator clocks. During this count, VCC must remain above VRST or the process restarts. If
an off-chip clock source is used, then clock counting still begins once VCC > VRST. This count period is
used to make certain that power is within tolerance, and that the oscillator has time to stabilize. This
provides a very controlled and predictable start-up condition.
Once the 65536 count period has elapsed, the reset condition is removed automatically, and software
execution will begin at the reset vector location of 0000h. Software will be able to detect the power on
reset condition using the Power-On Reset (POR) flag. POR is located at WDCON.6. This bit will be
high to indicate that a Power-on Reset has occurred. It should then be cleared by software.
The complete power cycle operation is shown in Figure 7-1. Note that the interrupt threshold is fixed, but
the interrupt itself is optional. Reset thresholds are also fixed and the reset operation is transparent. It
requires no external components and no action by software to control reset operation.
BAND-GAP SELECT
When present, the band-gap reference will provide a precise voltage reference for the power-fail monitor
circuitry. The band-gap is normally disabled automatically upon entering Stop mode to provide the
lowest power state. Since the band-gap is inactive, there can be no power-fail interrupt and no power-fail
reset, similar to a traditional 8051.
If the use of the power-fail features are desired in Stop mode, the BGS bit (EXIF, 91h) may be used.
When set to a logic 1 by software, the band-gap reference and associated power monitor circuits will
remain active in Stop mode. The price of this feature is higher power supply current requirements. In
Stop mode with the band-gap reference disabled (default), the processor draws approximately 1 µA.
With the band-gap enabled, it draws approximately 50 µA.
BGS allows the user to decide whether the control circuitry and its associated power consumption are
needed. If the application is such that power will not fail while in Stop or if it does not matter that power
fails, the BGS should be set to 0 (default). If power can fail at any time and cause problems, the BGS
should be set to 1.
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POWER CYCLE OPERATION Figure 7-1
VCC
VPFW
VRST
VSS
INTERRUPT
SERVICE ROUTINE
tCSU
XTAL1
tPOR
INTERNAL RESET
WATCHDOG WAKE UP
The Watchdog Wake up is more of an application than a feature. It allows a system to enter the Idle
mode for power savings, then to wake up periodically to sample the external world. Idle mode is a low
power state described below. Any of the programmable timers can perform this function, but the
Watchdog allows a much longer period to be selected. At 12 MHz, the maximum Watchdog time-out is
over 5.5 seconds. This contrasts with 0.78 seconds using the 16-bit timers. Software that uses the
Watchdog as a wake up alarm should only enable the Watchdog Interrupt and not the Reset. Note that the
Watchdog cannot be used to wake the system while in Stop mode since no clocks are running. Stop mode
is described below.
POWER MANAGEMENT SUMMARY
The following is a summary of the power management bits and those that are useful or related. They are
contained in the register locations WDCON;D8h, EIE;E8h, EXIF;91h, and PCON; 87h.
WDCON.6 POR - Power on Reset. Hardware will set this bit on a power up condition. Software can
read it, but must clear it manually. This bit assists software in determining the cause of a reset.
WDCON.5 EPFI - Enable Power-fail Interrupt. Setting this bit to 1 enables the Power-fail interrupt.
This will occur when VCC drops to approximately 4.5 volts, and the processor vectors to location 33h.
Setting this bit to a 0 turns off the Power-fail Interrupt.
WDCON.4 PFI - Power Fail Interrupt Flag. Hardware will set this bit to a 1 when a Power-fail condition
occurs. Software must clear the bit manually. Writing a 1 to this bit will force an interrupt, if enabled.
WDCON.3 WDIF - Watchdog Interrupt Flag. If the Watchdog Interrupt is enabled (EIE.4), hardware
will set this bit to indicate that the Watchdog Interrupt has occurred. If the interrupt is not enabled, this
bit indicates that the time-out has passed. If the Watchdog Reset is enabled (WDCON.1), the user has
512 clocks to strobe the Watchdog prior to a reset. Software or any reset can
clear this flag.
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WDCON.2 WTRF - Watchdog Timer Reset Flag. Hardware will set this bit when the Watchdog Timer
causes a reset. Software can read it, but must clear it manually. A Power-fail Reset will also clear the bit.
This bit assists software in determining the cause of a reset. If EWT=0, the Watchdog Timer will have no
affect on this bit.
WDCON.1 EWT - Enable Watchdog Timer Reset. Setting this bit will turn on the Watchdog Timer
Reset function. The Interrupt will not occur unless the EWDI bit in the EIE register is set. A reset will
occur according to the WD1 and WD0 bits in the CKCON register. Setting this bit to a 0 will disable the
reset but leave the timer running.
WDCON.0 RWT - Reset Watchdog Timer. This bit serves as the strobe for the Watchdog function.
During the time-out period, software must set the RWT bit if the Watchdog is enabled. Failing to set the
RWT will cause a reset when the time-out has elapsed. There is no need to set the RWT bit to a 0
because it is self-clearing.
EIE.4 EWDI - Enable Watchdog Interrupt. Setting this bit in software enables the Watchdog Interrupt.
EXIF.0 BGS - Band-Gap Select. Setting this bit to a 1 will allow the use of the Band-gap voltage
reference while in Stop mode. Since this function uses as much as 50 mA, the band-gap is optional in
Stop mode. Setting this bit to a 0 will turn off the Band-gap while in Stop mode. When BGS=0, no
Power-fail interrupt or Power-fail Reset will be available in Stop mode.
PCON.1 STOP. When this bit is set, the program stops execution, clocks are stopped, and the CPU
enters power-down mode.
PCON.0 IDLE. Program execution halts leaving timers, serial ports, and clocks running.
EXIF.2 RGMD - Ring Oscillator Mode. Hardware will set this status bit to a 1 when the clock source is
the Ring Oscillator. Hardware will set this status bit to a 0 when the crystal is the clock source. Refer to
RGSL below for operation of the Ring Oscillator.
EXIF.1 RGSL - Ring Oscillator Select. When set to a 1 by software, the High-Speed Microcontroller
will use a Ring Oscillator to come out of Stop mode without waiting for crystal start-up. This allows an
instantaneous start-up when coming out of Stop mode. It is useful if software needs to perform a short
task, then return to Stop. It is also useful if software must respond quickly to an external event. After the
crystal has performed 65,536 cycles, hardware will switch to the crystal as its clock source. The RGMD
status bit reports on this changeover. When RGSL is set to a 0, the High-Speed Microcontroller will
delay software execution until after the 65,536 clock crystal startup time. RGSL is only cleared by a
power-on reset and is not altered by other forms of reset.
POWER CONSERVATION
The High-Speed Microcontroller is implemented using full CMOS circuitry for low power operation. It
is fully static so the clock speed can be run down to DC. Like other CMOS, the power consumption is
also a function of operating frequency. Although the High-Speed Microcontroller is designed for
maximum performance, it also provides improved power versus work relationships compared with
standard 8051 devices. These topics are discussed in detail below.
The High-Speed Microcontroller provides two power conservation modes. They are similar, but have
different merits and drawbacks. These modes are Idle and Stop. In the original 8051, the Stop mode is
called Power Down. These modes are invoked in the same manner as the original 8051 series.
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IDLE MODE
Idle mode suspends all CPU processing by holding the program counter in a static state. No program
values are fetched and no processing occurs. This saves considerable power versus full operation. The
virtue of Idle mode is that it uses half the power of the operating state, yet reacts instantly to any interrupt
conditions. All clocks remain active so the timers, Watchdog, Serial Port, and Power Monitor functions
are all working. Since all clocks are running, the CPU can exit the Idle state using any of the interrupt
sources.
Software can invoke the Idle mode by setting the IDLE bit in the PCON register at location 87h. The bit
is located at PCON.0. The instruction that executes this step will be the last instruction prior to freezing
the program counter. Once in Idle, all resources are preserved. There are two ways to exit the Idle mode.
First, any interrupt (that is enabled) will cause an exit. This will result in a jump to the appropriate
interrupt vector. The IDLE bit in the PCON register will be cleared automatically. On returning from
this vector using the RETI instruction, the next address will be the one immediately after the instruction
that invoked the Idle state.
The Idle mode can also be removed using a reset. Any of the three reset sources can do this. On
receiving the reset stimulus, the CPU will be placed in a reset state and the Idle condition cleared. When
the reset stimulus is removed, software will begin execution as for any reset. Since all clocks are active,
there will be no delay after the reset stimulus is removed. Note that if enabled, the Watchdog Timer
continues to run during Idle and must be supported.
STOP MODE
Stop mode is the lowest power state that the High-Speed Microcontroller can enter. This is achieved by
stopping all on-chip clocks, resulting in a fully static condition. No processing is possible, timers are
stopped, and no serial communication is possible. Processor operation will halt on the instruction that
sets the STOP bit. The internal amplifier that excites the external crystal will be disabled, halting crystal
oscillation in Stop mode. Table 7-1 shows the state of the processor pins in Idle and Stop modes.
Stop mode can be exited in two ways. First, like the 8052 microcontrollers, a non-clocked interrupt such
as the external interrupts or the power-fail interrupt can be used. Clocked interrupts such as the watchdog
timer, internal timers, and serial ports will not operate in Stop mode. Note that the band-gap reference
must be enabled in order to use the power-fail interrupt to exit Stop mode, which will increase Stop mode
current. Processor operation will resume with the fetching of the interrupt vector associated with the
interrupt that caused the exit from Stop mode. When the interrupt service routine is complete, an RETI
will return the program to the instruction immediately following the one that invoked the Stop mode.
A second method of exiting Stop mode is with a reset. The watchdog timer reset is not available as a
reset source because no timers are running in Stop mode. An external reset via the RST pin will
unconditionally exit the device from Stop mode. If the BGS bit is set, the device will provide a reset
while in Stop mode if VCC should drop below the VRST level. If the BGS bit is 0, then a dip in power
below VRST will not cause a reset. For example, if VCC should drop to a level of VRST -0.5V, then return
to the full level, no reset will be generated. For this reason, use of the band–gap reference is
recommended if a brownout condition is possible in Stop mode. If power fails completely (VCC =0V),
then a power on reset will still be performed when VCC is reapplied regardless of the state of the BGS bit.
Processor operation will resume execution from address 0000h like anyother reset.
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CRYSTAL RESUME FROM STOP MODE
If the microcontroller does not contain a ring oscillator, or if the RGSL bit is 0, a device exiting Stop
mode must restart operation using the external crystal as a clock source. The device will experience a
power-on reset delay of 65536 external clock cycles to allow the crystal to begin oscillation and the
frequency to stabilize. Once this delay is complete, software will begin execution from either address
0000h or the appropriate interrupt vector, depending on the stimulus to exit Stop mode. The same 65536
external clock cycle delay is performed if an external crystal oscillator is used instead of an external
crystal.
PIN STATES IN POWER SAVING MODES Table 7-1
DEVICE
DS80C310
DS80C320
All Others
Internal program
execution
All Others
External program
execution
All Others
External program
execution
MODE
ALE
PSEN
P0 (AD0–7)
1
P1
Port data
P2
2
Latched
P3
3
Port data2
Idle or Stop
1
1
Latched
Idle or
1
1
Port data2
Port data2
Port data2
Port data2
Idle
1
1
Latched1
Port data2
Latched3
Port data2
Stop
1
1
Port data 2
Port data2
Port data4
Port data2
Stop
1
Port exhibits opcode following instruction that sets the Stop bit. Port 0 is operating in true bi-directional
mode, and will drive both a logic 1 and a logic 0.
2
Port reflects data stored in corresponding Port SFR. Port 0 functions as an open-drain output in this
mode.
3
Port exhibits address MSB of opcode following instruction that sets the Stop bit.
4
Port reflects data stored in corresponding Port SFR. In this mode, the port uses weak pull-ups. If a bit in
the P2 SFR is a 1, the corresponding device pin will transition slowly to a high when the reset state is
entered.
RING OSCILLATOR WAKE UP FROM STOP
A typical low power application is to keep the processor in Stop mode most of the time. Periodically, the
system will wake up (using an external interrupt), take a reading of some condition, then return to sleep.
The duration of full power operation is as short as possible. One disadvantage to this method is that the
clock must be restarted prior to performing a meaningful operation. This start-up period is a waste of
time and power since no work can be performed. The High-Speed Microcontroller provides an
alternative.
If the Ring Select (RGSL) is enabled, the High-Speed Microcontroller can exit Stop mode running from
an internal Ring Oscillator. Upon receipt of an interrupt, this oscillator can start instantaneously,
allowing software execution to begin immediately while the oscillator is stabilizing. Once 65,536 clock
cycles have been detected, the CPU will automatically switch to the normal oscillator as its clock source.
Some devices incorporate the option of continuing to run from the ring oscillator following Stop mode
even after the 65,536 clock cycle period. However, if the required interrupt response is very short, the
software can re-enter Stop mode before the crystal is even stable. In this case, Stop mode can be invoked
and both oscillators will be stopped.
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SPEED REDUCTION
The High-Speed Microcontroller is a fully CMOS 8051 compatible microcontroller. It can use
significantly less power than other 8051 versions because it is more efficient. As an average, software
will run 2.5 times faster on the High-Speed Microcontroller than on other 8051 derivatives. Thus the
same job can be accomplished by slowing down the crystal by a factor of 2.5. For example, an existing
8051 design that runs at 12 MHz can run at approximately 4.8 MHz on the High-Speed Microcontroller.
At this reduced speed, the High-Speed Microcontroller will have lower power consumption than an 8051,
yet perform the same job.
Using the 2.5X factor, Table 7-2 shows the approximate speed at which the High-Speed Microcontroller
can accomplish the same work as an 8051. The exact improvement will vary depending on the actual
instruction mix. Available crystal speeds must also be considered. Refer to Section 16 for information
on instruction timing.
CRYSTAL VS MIPS COMPARISON Table 7-2
ORIGINAL 8051
CRYSTAL SPEED
3.57 MHz
7.37 MHz
11.0592 MHz
14.318 MHz
16 MHz
20 MHz
24 MHz
33 MHz
40 MHz
MIPS
0.3
0.6
0.9
1.2
1.3
1.6
2.0
2.7
3.3
HIGH–SPEED MICROCONTROLLER
CRYSTAL SPEED
1.4 MHz
2.9 MHz
4.4 MHz
5.7 MHz
6.4 MHz
8 MHz
9.6 MHz
13.2 MHz
16 MHz
POWER MANAGEMENT MODES
Power consumption in CMOS microcontrollers is a function of operating frequency. The Power
Management Mode (PMM) feature, available with some members of the High-Speed Microcontroller
family, allows software to dynamically match operating frequency and current consumption with the need
for processing power. Instead of the default 4 clocks per machine cycle, power management mode 1
(PMM1) and power management mode 2 (PMM2) utilize 64 and 1024 clocks per cycle respectively to
conserve power.
A number of special features have been added to enhance the function of the power management modes.
The switchback feature allows the device to almost instantaneously return to divide by 4 mode upon
acknowledgment of an external interrupt or a falling edge on a serial port receiver pin. The advantages of
this become apparent when one calculates the increased interrupt service time of a device operating in
PMM. In addition, a device operating in PMM would normally be unable to sample an incoming serial
transmission to properly receive it. The switchback feature, explained below, allows a device to return to
divide by 4 operation in time to receive incoming serial port data and process interrupts with no loss in
performance.
The DS87C520 and DS87C530 incorporate a Status register (STATUS;C5h) to prevent the device from
accidentally reducing the clock rate during the servicing of an external interrupt or serial port activity.
This register can be interrogated to determine if a high priority, low priority, or power fail interrupt is in
progress, or if serial port activity is occurring. Based on this information the software can delay or reject
a planned change in the clock divider rate.
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In addition, the DS87C520 and DS87C530 has the capability to operate from the internal ring oscillator
during normal operation, not only during the crystal warm-up period. Table 7-3 summarizes the new
control bits associated with the power management features.
POWER MANAGEMENT AND STATUS BIT SUMMARY Table 7-3
BIT NAME
CD1, CD0
LOCATION
PMR.7–6
SWB
PMR.5
PIP
STATUS.7
HIP
STATUS.6
LIP
STATUS.5
SPTA1
STATUS.3
SPRA1
STATUS.2
SPTA0
STATUS.1
SPRA0
STATUS.0
FUNCTION
Clock Divider Control
CD1 CD0 Osc Cycles per Machine Cycle
0
0 Reserved
0
1 4 (Reset Default)
1
0 64 (PMM1)
1
1 1024 (PMM2)
Switchback Enable
0=Interrupts and serial port activity will not affect
clock divider control bits
1=Enabled Interrupts and serial port activity will
cause a switchback
Power Fail Interrupt Status
0=No power fail interrupt in progress
1=Power fail interrupt in progress
High Priority Interrupt Status
0=No high priority interrupt in progress
1=High priority interrupt in progress
Low Priority Interrupt Status
0=No low priority interrupt in progress
1=Low priority interrupt in progress
Serial Port 1 Transmitter Activity Status
0=Serial port 1 transmitter inactive
1=Serial port 1 transmitter active
Serial Port 1 Receiver Activity Status
0=Serial port 1 receiver inactive
1=Serial port 1 receiver active
Serial Port 0 Transmitter Activity Status
0=Serial port 0 transmitter inactive
1=Serial port 0 transmitter active
Serial Port 0 Receiver Activity Status
0=Serial port 0 receiver inactive
1=Serial port 0 receiver active
RESET
STATE
0,1
READ/WRITE
ACCESS
Write: 0,1 anytime;
1,0 & 1,1 only when
previously in 0,1
state. Unrestricted
read.
0
Unrestricted
0
Read Only
0
Read Only
0
Read Only
0
Read Only
0
Read Only
0
Read Only
0
Read Only
POWER MANAGEMENT MODE TIMING
The two power management modes reduce power consumption by internally dividing the clock signal to
the device, causing it to operate at a reduced speed. When PMM is invoked, the external crystal will
continue to operate at full speed. The difference is that the device uses 16 (PMM1) or 256 (PMM2)
external clocks to generate each internal clock cycle (C1, C2, C3 or C4) as opposed to 1 clock per internal
clock cycle in divide by 4 mode. This translates to 64 or 1024 external clocks per machine cycle in
PMM1 or PMM2, respectively. Relative timing relationships of all signals when the device is operating
in PMM1 or PMM2 will remain the same as the 4 cycle timing. Note that all internal functions, on-board
timers (including serial port baud rate generation), watchdog timer, and software timing loops will also
run at the reduced speed. Most applications will not find it necessary to attend to this much detail, but the
information is provided for calculating critical timings. Figure 7-2 demonstrates the internal timing
relationships during PMM1.
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INTERNAL TIMING RELATIONSHIPS IN PMM1 Figure 7-2
MACHINE
CYCLES
C1
SINGLE-CYCLE INSTRUCTION
SINGLE-CYCLE
INSTRUCTION
MACHINE CYCLE
MACHINE CYCLE
C2
C3
C4
C1
C2
ALE
INTERNAL
CLOCK
(PMM1)
EXTERNAL
CLOCK
64 CLOCK CYCLES
PMM1 and PMM2 are entered and exited by setting the Clock Rate Divider bits (PMR.7-6). In addition, it
is possible use the switchback feature to effect a return to the divide by 4 mode from either power
management mode. This allows both hardware and software to cause an exit from PMM. Entry to or exit
from either PMM must be by the divide by 4 mode. This means that to switch from divide by 64 to
divide by 1024 and vice versa, one must first switch back to divide by 4 mode. Attempts to execute an
illegal speed change will be ignored and the bits will remain unchanged. It is the responsibility of the
software to test for serial port activity before attempting to change speed, as a modification of the clock
divider bits during a serial port operation will corrupt the data.
PMM AND PERIPHERAL FUNCTIONS
Timers 0, 1, and 2 will default on reset to a 12 clock per cycle operation to remain compatible with the
original 8051 timing. The timers can be individually configured to run at machine cycle timing (divide
by 4) by setting the relevant bits in the Clock Control Register (CKCON;8Eh). Because the timers derive
their time base from the internal clock, timers 0, 1, and 2 operate at reduced clock rates during PMM.
This will also affect the operation of the serial ports in PMM. In general, it is not possible to generate
standard baud rates while in PMM, and the user is advised to avoid PMM or use the switchback feature if
serial port operation is desired. Table 7-4 shows the effect of the clock divider value on timer operation.
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EFFECT OF CLOCK MODES ON TIMER OPERATION Table 7-4
CD1 CD0
0
0
0
1
0
1
0
1
OSC.
CYCLES PER
MACHINE
CYCLE
Reserved
4
64 (PMM1)
1024 (PMM2)
OSC. CYCLES
PER TIMER
0/1/2 CLOCK
OSC. CYCLES
PER TIMER 2
CLOCK,BAUD
RATE GEN.
OSC. CYCLES
PER SERIAL
PORT CLOCK
MODE 0
OSC. CYCLES PER
SERIAL
PORT CLOCK
MODE 2
TxM=1
TxM=0
T2M=1
T2M=0
SM2=0
SM2=1
SMOD=0
SMOD=1
12
192
3072
4
64
1024
2
32
512
2
32
512
12
3072
1024
4
64
1024
64
1024
16,348
32
512
8192
SWITCHBACK
The switchback feature solves one of the most vexing dilemmas faced by power-conscious systems.
Many applications are unable to use the Stop and Idle modes because they require constant computation.
Traditionally, system designers could not reduce the operating speed below that required to process the
fastest event. This meant that system architects would be forced to operate their systems at the highest
rate of speed even when it was not required. The switchback feature allows a system to operate at a
relatively slow speed, and burst to a faster mode when required by an external event. When this feature is
enabled by setting the Switchback Enable bit, SWB, (PMR.5), a qualified interrupt or serial port reception
or transmission will cause the device to return to divide by 4 mode. A qualified interrupt is defined as an
interrupt which has occurred and been acknowledged. This means that an interrupt must be enabled and
also not blocked by a higher priority interrupt. After the event is complete, software can manually return
the device to the appropriate PMM. The following sources can trigger a switchback:
external interrupt 0/1/2/3/4/5,
serial start bit detected, Serial Port 0/1,
transmit buffer loaded, Serial Port 0/1,
watchdog timer reset,
power–on reset,
external reset.
In the case of a serial port-initiated switchback, the switchback is not generated by the associated
interrupt. This is because a device operating in PMM will not be able to correctly receive a byte of data
to generate an interrupt. Instead, a switchback is generated by a serial port reception on the falling edge
associated with the start bit, if the associated receiver enable bit (SCON0.4 or SCON1.4) is set. For serial
port transmissions, a switchback is generated when the serial port buffer (SBUF0;99h or SBUF1;C1h) is
loaded. This ensures the device will be operating in divide by 4 mode when the data is transmitted, and
eliminates the need for a write to the CD1, CD0 bits to exit PMM before transmitting. The switchback
feature is unaffected by the state of the serial port interrupt flags (RI_0, TI_0, RI_1, TI_1).
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The timing of the switchback is dependent on the source. Interrupt–initiated switchbacks will occur at the
start of the first C1 cycle following the event initiating the switchback. In PMM, each internal Cx cycle
is 16 external clock cycles for PMM1 and 256 cycles for PMM2. If the current instruction in progress is
a write to the IE, IP, EIE, or EIP registers, interrupt processing will be delayed until the completion of the
following instruction. Serial transmit-initiated switchbacks occur at the start of the instruction following
the MOV that loads SBUF0 or SBUF1. Serial reception-initiated switchbacks occur during the Cx cycle
in which the falling edge was detected. There are a few points that must be considered when using a
serial port reception to generate a switchback. Under normal circumstances, noise on the line or an
aborted transmission would cause the serial port to time-out and the data to be ignored. This presents a
problem if the switchback is used, however, because a switchback would occur but there is no indication
to the system that one has occurred. If PMM and serial port switchback functions are used in a noisy
environment, the user is advised to periodically check if the device has accidentally exited PMM.
A similar problem can occur if multiprocessor communication protocols are used in conjunction with
PMM. The High-Speed Microcontroller family supports both the use of the SM2 flag (SCON0.5 or
SCON1.5), and the slave address recognition registers (SADDR0;A9h, SADDR1;AAh, SADEN0;B9h,
SADEN1;BAh) for multiprocessor communications. The problem is that an invalid address which should
be ignored by a particular processor will still generate a switchback. As a result it is not recommended to
use a multiprocessor communication scheme in conjunction with PMM. If the system
power considerations will allow for an occasional erroneous switchback, a polling scheme can be used to
place the device back into PMM.
CLOCK SOURCE SELECTION
The High-Speed Microcontroller family supports three different clock sources for operation. As with
most microcontrollers, the device can be clocked from an external crystal using the on-board crystal
amplifier, or a clock source can supplied by an external oscillator. In addition, some members of the
High-Speed Microcontroller family incorporate an on-board ring oscillator to provide a quick resumption
from Stop mode. The ring oscillator is a low power digital oscillator internal to the microcontroller.
When enabled, it provides an approximately 2-4 MHz clock source for device operation without external
components. The ring oscillator is not as stable as an external crystal, and software should refrain from
performing timing dependent operations, including serial port activity, while operating from the ring
oscillator.
The ring oscillator provides many advantages to the designers of microcontroller-based systems. One is
that it allows Dallas Semiconductor microcontrollers to perform a fast resume from Stop mode,
eliminating the crystal warm-up delay when restarting the device. As an added feature, the DS87C520
and DS87C530 will also support extended operation from the ring oscillator, not only during the crystal
warm-up period when resuming from Stop. All devices in the High-Speed Microcontroller
family must begin operation following a power-on reset from an external clock source, either an external
crystal or oscillator. Software can then disable the crystal and run from the lower power ring oscillator.
The control and status bits which support the new and/or enhanced features are shown in Table 7-5.
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CLOCK CONTROL AND STATUS BIT SUMMARY Table 7-5
BIT
NAME
LOCATION
XT/ RG
EXIF.3
RGMD
EXIF.2
RGSL
EXIF.1
XTOFF
PMR.3
XTUP
STATUS.4
FUNCTION
RESET
WRITE ACCESS
Crystal/Ring Clock Source Select. This bit is not present on
the 80C320.
1=Select crystal or external clock as clock source,
0=Select ring oscillator as clock source
Ring Oscillator Mode Status.
1=Ring oscillator is current clock source,
0=Crystal or external clock is current clock source.
Ring Oscillator Select, Stop Mode.
1=Ring oscillator will be the clock source when resuming
from Stop mode,
0=Crystal or external clock will be the clock
source when resuming from Stop mode
Note: Upon completion of crystal warm up period,
DS80C320 devices will switch to crystal.
DS87C520 and DS87C530 devices will switch to clock
source designated by XT/RG bit
1
0 anytime;
1 when XTUP=1
& XTOFF=0
0
None
Crystal Oscillator Disable. Disables crystal operation
after ring mode has been selected. This bit is not present on
the 80C320.
1=Crystal amplifier is disabled.
0=Crystal amplifier is enabled. Check XTUP for status.
Crystal Oscillator Warm Up Status. This bit is
not present on the 80C320.
1=Oscillator warm up complete.
0=Oscillator warm up still in progress, crystal not available.
0
Unrestricted
0 anytime;
1 when XT/ RG =0
1
None
USING THE RING OSCILLATOR
The ring oscillator is an internal 2-4 MHz clock source used to quickly exit Stop mode and resume
operation without waiting for an external clock source to stabilize. Some devices feature the additional
capability of using the ring oscillator as the primary clock source during normal operation, once the
device has performed an initial power-on reset using an external clock source. Because the ring oscillator
lacks the stability of a piezoelectric-generated clock source, high-precision timing operations should be
avoided while running from the ring oscillator. This includes using the timers for pulse measurement,
and the use of the serial ports in asynchronous modes. Serial ports operating in mode 0 are unaffected by
the stability of the clock source because this mode utilizes a synchronizing clock.
If the Ring Oscillator Select bit, RGSL (EXIF.1) is set, the device will resume operation immediately
using the internal ring oscillator as the clock source. The device will continue to run from the ring
oscillator until the crystal warm-up period of 65,536 clock cycles (measured from the external source) has
completed. At this time the device will switch to the clock source active before it entered Stop mode and
continue operation. This allows software execution to begin immediately upon resuming from Stop
mode. The current clock source is indicated by the Ring Oscillator Mode bit, RGMD (EXIF.2). In Stop
mode, enabled interrupts become true edge triggered interrupts, compared with the sampled edge
detection used during normal operation. This means that external interrupts are more sensitive to noise in
Stop mode than during normal operation. Applications should be carefully designed to ensure that noise
will not cause an erroneous exit from Stop mode.
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SWITCHING BETWEEN CLOCK SOURCES
DS87C520 and DS87C530 incorporate the ability to run the device from the ring oscillator after the
crystal warm-up period has elapsed. Immediately following a reset (including initial power-up), all
devices must operate from an external crystal or oscillator. At this point, software may switch to the ring
oscillator by clearing the XT/ RG bit (EXIF.3). If there is no expectation that the crystal oscillator will be
needed soon, the crystal oscillator can be disabled by setting the Crystal Oscillator Disable Bit, XTOFF
(PMR.3). Note that switching to the ring oscillator does not automatically disable the crystal amplifier,
and thus it is possible to be operating the device from the ring oscillator and have the external crystal
amplifier operating at the same time. In some cases this may be desired to take advantage of the lowfrequency, low-power feature of the ring oscillator but still have the capability of quickly switching back
to the external crystal to perform timing or serial port operations.
Switching from the ring oscillator to the crystal oscillator is more involved due to the startup delays
inherent in the external crystal. To prevent an accidental disabling of the device, the XTUP bit must be
set by internal hardware (indicating an enabled, stable crystal) before setting the XT/ RG bit. The
procedure to switch to the crystal oscillator when running from the ring oscillator is as follows:
1. Clear the Crystal Oscillator Disable Bit, XTOFF (PMR.3) to restart the crystal oscillator and start the
crystal warm-up period.
2. Wait for the Crystal Oscillator Warm Up Status bit, XTUP (STATUS.4) to be set, indicating that the
external crystal warm up period is complete. This will take 65,536 external clock cycles.
3. Set the Crystal Oscillator/Ring Oscillator Select Bit, XT/ RG (EXIF.3) to select the crystal as the
clock source.
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SECTION 8: RESET CONDITIONS
The High-Speed Microcontroller provides several ways to place the CPU in a reset state. It also offers
the means for software to determine the cause of a reset. The reset state of most processor bits is not
dependent on the type of reset, but selected bits do depend on the reset source. The reset sources and the
reset state are described below.
RESET SOURCES
The High-Speed Microcontroller has three ways of entering a reset state. Each reset source is described
below. They are:
Power-on/Power Fail Reset
Watchdog Timer Reset
External Reset
Power-on/Fail Reset
Members of the High-Speed Microcontroller family incorporate an internal voltage reference which holds
the CPU in the power-on reset state while VCC is out of tolerance. Once VCC has risen above the
threshold, the microcontroller will restart the oscillation of the external crystal and count 65536 clock
cycles. The processor will then begin software execution at location 0000h.
The voltage at which the reset state is entered depends on the specific device. If the device does not
contain a precision voltage reference, the power-on reset threshold may be anywhere between 0.8V and
VCCMIN . If the device incorporates a precision voltage reference, the threshold will be as specified by the
VRST parameter in the data sheet. This helps the system maintain reliable operation by only permitting
processor operation when voltage is in a know good state.
The processor will exit the reset condition automatically once the above conditions are met. This happens
automatically, needing no external components or action. Execution begins at the standard reset vector
address of 0000h. Software can determine that a Power-on Reset has occurred using the Power-on Reset
flag (POR). It is located at WDCON.6. Since all resets cause a vector to location 0000h, the POR flag
allows software to acknowledge that power failure was the reason for a reset.
Software should clear the POR bit after reading it. When a reset occurs, software will be able to
determine if a power cycle was the cause. In this way, processing may take a different course for each of
the three resets if applicable. When power fails (drops below VRST ), the power monitor will invoke the
reset state again. This reset condition will remain while power is below the threshold. When power
returns above the reset threshold, a full power-on reset will be performed. Thus a brownout that causes
VCC to drop below VRST appears the same as a power up.
Watchdog Timer Reset
The Watchdog Timer is a free running timer with a programmable interval. Software can clear the timer
at anytime, causing the interval to begin again. The Watchdog supervises CPU operation by requiring
software to clear it before the time-out expires. If the timer is enabled and software fails to clear it before
this interval expires, the CPU is placed into a reset state. The reset state will be maintained for two
machine cycles. Once the reset is removed, the software will resume execution at 0000h.
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The Watchdog Timer is fully described in Section 11. Software can determine that a Watchdog time-out
was the reason for the reset by using the Watchdog Timer Reset flag (WTRF). WTRF is located at
WDCON.2. Hardware will set this bit to a logic 1 when the Watchdog times out without being cleared by
software if EWT=1. If a Watchdog Timer reset occurs, software should clear this flag manually. This
allows software to detect the event if it occurs again.
External Reset
If the RST input is taken to a logic 1, the CPU will be forced into a reset state. This will not occur
instantaneously, as the condition must be detected and then clocked into the microcontroller. It requires a
minimum of two machine cycles to detect and invoke the reset state. Thus the reset is a synchronous
operation and the crystal must be running to cause an external reset.
Once the reset state is invoked, it will be maintained as long as RST=1. When the RST is removed, the
CPU will exit the reset state within two machine cycles and begin execution at address 0000h. All
registers will default to their power-on reset state. There is no flag to indicate that an external reset was
applied. However, since the other two sources have associated flags, the RST pin is the default source
when neither POR or WTRF is set.
If a RST is applied while the processor is in the Stop mode, the scenario changes slightly. As mentioned
above, the reset is synchronous and requires a clock to be running. Since the Stop mode stops all clocks,
the RST will first cause the oscillator to begin running and force the program counter to 0000h. Rather
than a two machine cycle delay as described above, the processor will apply the full power-on delay
(65536 clocks) to allow the oscillator to stabilize.
RESET STATE
Regardless of the source of the reset, the state of the microcontroller is the same while in reset. When in
reset, the oscillator is running, but no program execution is allowed. When the reset source is external,
the user must remove the reset stimulus. When power is applied to the device, the power-on delay
removes the stimulus automatically.
Resets do not affect the Scratchpad RAM. Thus any data stored in RAM will be preserved. The contents
of internal MOVX data memory will also remain unaffected by a reset. Note that if the power supply
dips below approximately 2V, the RAM contents may be lost. The minimum voltage required for RAM
data retention in not specified. Since it is impossible to determine if the power was lower than 2V prior
to the power–on reset, RAM must be assumed lost when POR is set.
The reset state of SFR bits are described in Section 4. Bits which are marked SPECIAL have conditions
which can affect their reset state. Consult the individual bit descriptions for more information. Note that
the stack pointer will also be reset. Thus the stack is effectively lost during a reset even though the RAM
contents are not altered. Interrupts and Timers are disabled. The state of the Watchdog Timer is
dependent on the specific device in use. Note that the Watchdog time out defaults to its shortest interval
on any reset. I/O Ports are taken to a weak high state (FFh). This leaves each port pin configured with
the data latch set to a 1. Ports do not go to the 1 state instantly when a reset is applied, but will be taken
high within two machine cycles of asserting a reset. When the reset stimulus is removed, program
execution begins at address 0000h.
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NO-BATTERY RESET
The battery backup feature of the DS87C530 introduces a new type of reset condition. Most SFR bits are
automatically reset to their default state upon a power-on reset. The external backup battery feature
makes some bits non-volatile, however, and these battery-backed bits will not change state when a poweron reset is applied. Upon the loss or initial connection of battery power these bits will default to the state
shown in Table 8-1. Any bits not listed below are either unchanged or set to their default state by a
power-on reset.
NO–BATTERY RESET DEFAULT Table 8-1
BIT NAME
E4K
X12/6
TRM2
TRM2
TRM1
TRM1
TRM0
TRM0
RTASS.7–0
RTAS.7–0
RTAM.7–0
RTAH.7–0
LOCATION
TRIM.7
TRIM.6
TRIM.5
TRIM.4
TRIM.3
TRIM.2
TRIM.1
TRIM.0
RTASS.7–0
RTAS.7–0
RTAM.7–0
RTAH.7–0
NO-BATTERY
RESET
STATE
0
1
1
0
0
1
0
1
Indeterminate
Indeterminate
Indeterminate
Indeterminate
BIT NAME
SSCE
SCE
MCE
HCE
RTCIF
RTCE
RTCSS.7–0
RTCS.7–0
RTCM.7–0
RTCH.7–0
RTCD0.7–0
RTCD1.7–0
LOCATION
RTCC.7
RTCC.6
RTCC.5
RTCC.4
RTCC.1
RTCC.0
RTCSS.7–0
RTCS.7–0
RTCM.7–0
RTCH.7–0
RTCD1.7–0
RTCD1.7–0
NO-BATTERY
RESET
STATE
Indeterminate
Indeterminate
Indeterminate
Indeterminate
Indeterminate
Indeterminate
Indeterminate
Indeterminate
Indeterminate
Indeterminate
Indeterminate
Indeterminate
IN-SYSTEM DISABLE MODE
The High-Speed Microcontroller Family supports in-circuit debugging of designs. The In-System Disable
(ISD) feature allows the device to be tristated for in-circuit emulation or board testing. During ISD mode,
the device pins will take on the following states:
DEVICE PIN
Port 0, 1, 2, 3 RST, EA
ALE, PSEN
XTAL1, XTAL2
STATE DURING ISD
True Tristate
Weak Pullup (~10KO)
Oscillator remains active
The following procedure is used to enter ISD mode:
1.
2.
3.
4.
5.
6.
Assert reset by pulling RST high,
Pull ALE low and pull PSEN high,
Verify that P2.7, P2.6, P2.5 are not being driven low,
Release RST,
Hold ALE low and PSEN high for at least 2 machine cycles,
Device is now in ISD mode. Release ALE and PSEN if desired.
Note that pins P2.7, P2.6, P2.5 should not be driven low when RST is released. This will place the device
into a reserved test mode. Because these pins have a weak pull-up during reset, they can be left floating.
The test mode is only sampled on the falling edge of RST, and once RST is released their state will not
effect device operation. In a similar manner, the PSEN and RST pins can be released once ISD mode is
invoked, and their state will not effect device operation. The RST pin will also be in a tristate mode, but
asserting it in ISD mode will return the device to normal operation.
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SECTION 9: INTERRUPTS
The High-Speed Microcontroller family utilizes a three-priority interrupt system. The number of
interrupts varies according to the specific device. Each source has an independent priority bit, flag,
interrupt vector, and enable. In addition, interrupts can be globally enabled (or disabled). The system is
compatible with the original 8051 family. All of the original interrupts are available.
Several new sources have been added with new associated control and status bits, and new interrupt
vectors. Note that the interrupt vector table can extend from 0000h to 006Bh, so existing code may
require a relocation of the start address to avoid a conflict with the upper end of the vector table. A
summary of all interrupts appears in Table 9-1 below. Note that the D587C550 microcontroller
incorporates several interrupt vectors whose locations differ from those used by the High-Speed
Microcontroller Family or other 8051 derivatives.
INTERRUPT SUMMARY Table 9-1
INTERRUPT
Power–fail Indicator
INTERRUPT
VECTOR
33h
NATURAL
PRIORITY
0
External Interrupt 0
Timer 0 Overflow
External Interrupt 1
Timer 1 Overflow
Serial Port 0
03h
0Bh
13h
1Bh
23h
1
2
3
4
5
Timer 2 Overflow
Serial Port 1
2Bh
3Bh
6
7
External Interrupt 2
External Interrupt 3
External Interrupt 4
External Interrupt 5
Watchdog Interrupt
Real –Time Clock
43h
4Bh
53h
5Bh
63h
6Bh
8
9
10
11
12
13
FLAG
ENABLE
PFI (WDCON.4)
EPFI
(WDCON.5)
EX0 (IE.0)
ET0 (IE.1)
EX1 (IE.2)
ET1 (IE.3)
ES0 (IE.4)
IE0 (TCON.1)**
TF0 (TCON.5)*
IE1 (TCON.3)**
TF1 (TCON.7)*
RI_0 (SCON0.0),
TI_0 (SCON0.1)
TF2 (T2CON.7)
RI_1 (SCON1.0),
TI_1 (SCON1.1)
IE2 (EXIF.4)
IE3 (EXIF.5)
IE4 (EXIF.6)
IE5 (EXIF.7)
WDIF (WDCON.3)
RTCIF (RTCC.1)
PRIORITY
CONTROL
N/A
PX0 (IP.0)
PT0 (IP.1)
PX1 (IP.2)
PT1 (IP.3)
PS0 (IP.4)
ET2 (IE.5)
ES1 (IE.6)
PT2 (IP.5)
PS1 (IP.6)
EX2 (EIE.0)
EX3 (EIE.1)
EX4 (EIE.2)
EX5 (EIE.3)
EWDI (EIE.4)
ERTCI (EIE.5)
PX2 (EIP.0)
PX3 (EIP.1)
PX4 (EIP.2)
PX5 (EIP.3)
PWDI (EIP.4)
PRTCI
(EIP.5)
Unless marked these flags must be cleared manually by software.
* Cleared automatically by hardware when the service routine is vectored to.
** If edge triggered, cleared automatically by hardware when the service routine is vectored to. If level
triggered, flag follows the state of the pin.
INTERRUPT OVERVIEW
An interrupt allows the software to react to unscheduled or asynchronous events. When an interrupt
occurs, the CPU is expected to “service” the interrupt. This service takes the form of an Interrupt Service
Routine (ISR). The ISR resides at a predetermined address as shown in Table 9-1. When the interrupt
occurs, the CPU will vector to the appropriate location. It will run the code found at this location, staying
in an interrupt service state until done with the ISR. Once an ISR has begun, it can be interrupted only by
a higher priority interrupt. The ISR is terminated by a return from interrupt instruction (RETI). When an
RETI is performed, the processor will return to the instruction that would have been next when the
interrupt occurred.
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Each interrupt source has an associated vector. This is the address to which the CPU will jump when the
interrupt occurs. When the interrupt condition occurs, the processor will also indicate this by setting a
flag bit. This bit is set regardless of whether the interrupt is enabled or not. That is, the flag responds to
the condition, not the interrupt. Most flags must be cleared manually by software. However, IE0 and IE1
are cleared automatically by hardware when the service routine is vectored to if the interrupt was edge
triggered. In level triggered mode, the flag follows the state of the pin. Flags TF0 and TF1 are always
cleared automatically when the service routine is vectored to. Refer to the individual bit descriptions
for more details. In order for the processor to acknowledge the interrupt and vector to the ISR, the
interrupt must be enabled. Each source has an independent enable as shown in Table 9-1.
Prior to using any source, interrupts must be globally enabled. This is done using the EA bit at location
IE.7. Setting this bit to a logic 1 allows individual interrupts to be enabled. Setting it to a logic 0 disables
all interrupts regardless of the individual interrupt enables. The only exception is the Power-fail
Interrupt. This is subject to its individual enable only. The EA bit has no effect on the Power-fail
Interrupt.
INTERRUPT SOURCES
Various combinations of interrupt sources are available on different members of the High-Speed
Microcontroller family. These are broken into several categories : External, Timer-based, Serial
Communication, real-time clock and Power Monitor. Each type is described below. Interrupt sources are
sampled once per machine cycle. If the source goes active after the sample, it will not be registered until
the next cycle.
External Interrupts
The High-Speed Microcontroller has 6 external interrupt sources. These include the standard 2 interrupts
of the 8051 architecture and 4 new sources. The original interrupts are INT0 and INT1. These are active
low, but can be programmed to be edge- or level-sensitive. The detection mode is controlled by bits IT0
and IT1, respectively. When ITx=0, the interrupt is triggered by a logic 0 on the appropriate interrupt
pin. The interrupt condition remains in force as long as the pin is low. When ITx=1, the interrupt is
pseudo edge-triggered. This means that if on successive samples, the pin is high then low, the interrupt is
activated.
Since the external interrupts are sampled, the pin driver of an edge-triggered interrupt should hold the
both the high, then the low condition for at least one machine cycles (each) to insure detection. This
means maximum sampling frequency on any interrupt pin is 1/8 of the main oscillator frequency.
It is important to note that level-sensitive interrupts are not latched. If the interrupt is level-sensitive, the
condition must be present until the processor can respond to the interrupt. This is most important if other
interrupts are being used with a higher or equal priority. If the device is currently processing another
interrupt, the condition must be present until the present interrupt is complete. This is because the levelsensitive interrupt will not be sampled until the RETI instruction is executed.
The remaining 4 external interrupts are similar in nature, with two differences. First, INT2 and INT4 are
active high instead of active low. Second, all of the four new interrupts are edge-detect only. They do
not have level-detect modes. All associated bits and flags operate the same and have the same polarity as
the original two. A logic 1 indicates the presence of a condition, not the logic state of the pin.
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If the Power Management Modes are utilized, the designer must remember that edge triggered interrupts
must be high and low for one machine cycle before being recognized. This means that in PMM1 it will
require 128 external clock cycles to recognize a level sensitive interrupt. Similarly, in PMM2 it will
require 2048 external clock cycles to recognize a level sensitive interrupt. As a result, the interrupt
latency for these interrupts will be slightly longer in PMM1or PMM2.
Timer Interrupts
The High-Speed Microcontroller incorporates three 16-bit programmable timers, each of which can
generate an interrupt. In addition, some members of the family incorporate a programmable watchdog
timer. The three programmable timers operate in the same manner as the 80C52. Each timer has an
independent interrupt enable, flag, vector, and priority. The Watchdog Timer also has its own interrupt
enable, flag, and priority.
Timers 0, 1, and 2 will set their respective flags when the timer overflows from a full condition,
depending on its mode. This flag will be set regardless of the interrupt enable state. If the interrupt is
enabled, this event will also cause a jump to the corresponding interrupt vector. For timers 0 and 1, the
flags are cleared when the processor jumps to the interrupt vector. Thus these flags are not available for
use by the interrupt service routine (ISR), but are available outside of the ISR and in applications that
don’t acknowledge the interrupt (i.e., jump to the vector). If the interrupt is not acknowledged, then
software must manually clear the flag bit. In timer 2, jumping to the interrupt vector does not clear the
flag, so software must always clear it manually. Timer 0 and 1 flag bits reside in the TCON register.
Timer 2 flag bit resides in the T2CON register. The interrupt enables and priorities for timers 0, 1, and 2
reside in the IE and IP registers respectively.
The Watchdog Interrupt usually has a different connotation than the Timer interrupts. Unless the
Watchdog is being used as a very long timer, the interrupt means the software has failed to reset the
counter and may be lost. The ISR can attempt to determine the system state. If the Watchdog is not
cleared, the CPU will be reset in 512 clocks if EWT=1. Like other sources, the Watchdog Timer has a
flag bit, an enable, and a priority. It also has its own vector. These are summarized in table 9-1.
Serial Communication Interrupts
Each UART is capable of generating an interrupt. The UART has its own interrupt enable, vector, and
priority. The UART differs from other sources as it has two flags. These are used by the ISR to
determine whether the interrupt comes from a received word or a transmitted one. Unlike the timers, the
UART flags are not altered when the interrupt is serviced. Software must change them manually.
When a UART finishes the transmission of a word, an interrupt will be generated (if enabled). Likewise,
the UART will generate an interrupt when a word is completely received. The CPU will not be notified
until the word is completely received or transmitted.
Real-Time Clock
The DS87C530 real-time clock (RTC) has the ability to assert an RTC interrupt if enabled. The alarm
can be programmed for a specific time once per day, or can be a recurring alarm once per hour, minute,
second, or subsecond. This interrupt has the lowest priority of all interrupts, but can be used to bring the
device out of Stop mode if desired. More information on this interrupt can be found in Section 14.
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Power-fail Interrupt
Some devices have the ability to generate an interrupt when VCC drops below a predetermined level.
These devices compare VCC against an internal reference. If VCC drops below the level VPFW , an
interrupt will result (if enabled). Note that the Power-fail Interrupt has the highest priority. The priority
level cannot be altered by the user, but the interrupt can be disabled if not needed. The level of VPFW is
provided in the data sheet specifications associated with each product. Note that the EPFI bit enables the
Power-fail Interrupt. This bit is not subject to the global interrupt enable (EA). The Power-fail interrupt
is a level-sensitive interrupt and will remain set as long as VCC remains below VPFW.
Simulated Interrupts
Software can simulate any interrupt source by setting the corresponding flag bit. This forces an interrupt
condition which will be acknowledged if enabled and is otherwise indistinguishable from the real thing.
Thus an interrupt flag bit should never be set to a logic 1 by software inadvertently. Once an interrupt has
been acknowledged, software cannot prevent or end the interrupt by clearing its flag. However, if for
some reason the interrupt acknowledge is delayed, software may clear the flag and thereby prevent the
interrupt from occurring. One exception is the real-time clock interrupt flag, RTCIF, which cannot be set
in software.
INTERRUPT PRIORITIES
The High-Speed Microcontroller has three interrupt priority levels. These are highest, high, and low.
The Power-fail Interrupt is the only source that has highest priority and this level is fixed. The remaining
sources are individually programmable to either high or low. Low priority is the default. A low priority
interrupt can be interrupted by a high (or highest) priority interrupt. A high priority interrupt can only be
interrupted by the Power-fail interrupt.
When an interrupt occurs and is serviced, its priority determines if its ISR can be interrupted. No
interrupt source of equal or lesser priority can interrupt another source. That is, an incoming interrupt
must be of a higher priority than the one currently being serviced to have priority.
If two interrupt sources of equal priority levels are requested simultaneously, the natural priority is used
to arbitrate. The natural priority is given in Table 9-1. Note that natural priority is only used to resolve
simultaneous requests. Once an interrupt of a given priority is invoked, only a source that is programmed
with a higher priority can intercede.
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INTERRUPT ACKNOWLEDGE CYCLE
The process of acknowledging an interrupt requires multiple machine cycles that begin with the setting of
the associated flag. For edge triggered external interrupts and internal interrupt sources, the interrupt
flags are set automatically by hardware. For level sensitive external interrupts, the flags are actually
under control of the external signal, and the flag will rise and fall with the pin level. Each interrupt flag is
sampled once per machine cycle. Later in the same machine cycle, the samples are polled by hardware.
If the sample indicates a pending interrupt and the interrupt is enabled, then on the next machine cycle it
will be acknowledged by the hardware forcing an LCALL to the appropriate vector address. This
LCALL will occur unless blocked by one of the following conditions.
1. An interrupt of equal or greater priority has already been invoked and the RETI instruction has not
been issued to terminate it.
2. The current machine cycle is not the final cycle in the execution of the current instruction.
3. The instruction in progress is an RETI or a write to IP, IE, EIP, or EIE.
The individual interrupt sources and associated enable and priority bits are shown in Figure 9-1. While
the final selection of the appropriate interrupt vector address is referred to as a polling process, this
function is actually performed in a single machine cycle using combinatorial logic.
INTERRUPT LATENCY
Interrupt response will require a varying amount of time depending on the state of the microcontroller
when the interrupt occurs. If the microcontroller is performing an ISR with equal or greater priority, the
new interrupt will not be invoked. In other cases, the response time depends on the current instruction.
The fastest possible response to an interrupt is 5 machine cycles. This includes one cycle for detecting
the interrupt and four cycles to perform the LCALL that is inherent in the interrupt request. The
maximum response time (if no other interrupt is in service) occurs if the microcontroller is performing an
RETI instruction, and then executes a MUL or DIV as the next instruction. From the time an interrupt
source is activated (not detected), the longest reaction time is 13 machine cycles. This includes 1 cycle to
detect the interrupt, 3 cycles to finish the RETI, 5 to perform the MUL or DIV, then 4 for the LCALL to
the ISR.
The maximum latency of 13 machine cycle is 52 clocks (13*4). Note that the maximum interrupt latency
of an 8051 is 96 clocks (8 machine cycles @ 12 clocks per machine cycle). The maximum latency for the
High-Speed Microcontroller at 25 MHz is about 2 µs. The use of Power Management modes can further
increase the interrupt latency.
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INTERRUPT FUNCTIONAL DESCRIPTION Figure 9-1
FLAG
BITS
INTERRUPT
SELECTION
HARDWARE
INTERRUPT
ENABLE BITS
HIGHEST
PRIORITY
PFI
HI=1
INT0
HI=0
TF0
INT1
IT1
TF1
RI_0
TI_0
INTERRUPT
VECTOR
TF2
RI_1
TI_1
INT2
INT3
INT4
INT5
WATCHDOG
REAL-TIME
CLOCK
LOWEST
PRIORITY
INDIVIDUAL GLOBAL
ENABLES ENABLE
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INTERRUPT REGISTER CONFLICTS
During normal operation there is a small but finite probability that application software may try to read or
modify a register associated with interrupt functions at the same time that the interrupt hardware is
modifying the register. In general, these hardware/software interrupt conflicts are resolved according to
the "hardware wins" philosophy: In the event of a conflict, the hardware modification of a register will
take precedence over the software action to ensure that the interrupt event is not missed.
Software should always use read-modify-write instructions when modifying registers associated with
interrupt functions. This special class of instructions evaluates and modifies register contents in a single
instruction, preventing the hardware from accidentally modifying a bit between the time it is read and
when it is written back to the register.
One specific case involves a software write to the IP, IE, EIP or EIE registers while the internal interrupt
hardware is processing an interrupt request. Interrupt sources are normally executed (i.e., the LCALL
instruction is performed) during the instruction following their detection. If an interrupt is detected during
a write to one of the previously mentioned registers, it is possible that it will be delayed for one additional
instruction. When the instruction is processed, the interrupt will incorporate the new priority and enable
values from the previous instruction. If this situation occurs it will lengthen the interrupt latency by the
length of the instruction that modified the register.
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SECTION 10: PARALLEL I/O
The High-Speed Microcontroller method of implementing I/O ports follows the standard 8051
convention. This provides backward compatibility with existing designs. All drive capabilities exceed or
equal the original 80C32, and voltage levels are compatible. The transitions between strong and weak
drives are similar but not identical. Differences are to accommodate higher speed timing and the
associated demands on slew rates. As with any new technology, the High-Speed Microcontroller
should be evaluated in a system to see how subtle differences affect operation.
From a software perspective, each port appears as Special Function Register (SFR) with a unique address.
Each port register is addressable as a byte or 8 individual bit locations. The CPU distinguishes between a
bit access and a byte access by the instruction type. Except for the special cases mentioned below, the
register and port pins have identical states. Thus reading or writing a port is the same as reading or
writing the SFR for that port.
The microcontroller will distinguish between port and bus operations automatically. If a memory fetch is
decoded and requires external memory, Port 0 and 2 will be driven as a bus with the associated timing
and drive strengths. If either port SFR is accessed, the port pins will revert to the characteristics
described above. This includes a strong pull-down, a strong pull–up for transitions, and a weak pull-up
for static conditions.
ROMless versions of the High-Speed Microcontroller dedicate Port 0 and 2 as the memory interface bus.
The Port 0 latch does not exist on ROMless devices. The functions of these ports are described in more
detail in the specific sections.
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PORT 0
General Purpose I/O
Devices which have internal program memory have the ability to use Port 0 as a general purpose I/O.
Data written to the port latch serves to set both level and direction of the data on the pin. ROMless
devices do not contain a Port 0 latch, because at no time can it be manipulated as a port. When used as an
I/O port, it functions as an open-drain output. More detail on the functions of these pins is provided
under the description of output and input functions in this section.
Even if internal memory is present, the use of Port 0 as general purpose I/O pins is not recommended if
the device will be used to access external memory. This is because the state of the pins will be disturbed
during the memory access. In addition, the pull-ups needed to maintain a high state during the use as
general purpose I/O will interfere with the complementary drivers employed when the device operates as
an expanded memory bus.
Multiplexed Address/Data Bus AD0-7
When used to address expanded memory, Port 0 functions as a multiplexed address/data bus. Port 0 must
function as the address/data bus on ROMless devices. Port 0 pins have extremely strong drivers that
allow the bus to move 100 pF loads with the timing shown in the electrical specifications. Special circuit
protection allows these pins to achieve the maximum slew rate without ringing, eliminating excessive
noise or interface problems. Users that compare the High-Speed Microcontroller family to 80C32
devices will find improved drive capability. This power is available for dynamic switching only, and
should not be used to drive heavy DC loads such as LEDs.
When used as an address bus, the AD0-7 pins will provide true drive capability for both logic levels. No
pull-ups are needed. In fact, pull-ups will degrade the memory interface timing. Members of the HighSpeed Microcontroller family employ a two-state drive system on AD0-7. That is, the pin is driven hard
for a period to allow the greatest possible setup or access time. Then the pin states are held in a weak
latch until forced to the next state or overwritten by an external device. This assures a smooth transition
between logic states and also allows a longer hold time. In general, the data is held (hold time) on AD0-7
until another device overwrites the bus. This latch effect is generally transparent to the user.
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PORT 0 FUNCTIONAL CIRCUITRY Figure 10-1
EXTERNAL
ADDRESS
CONTROL
ADDRESS\
DATA
VCC
PORT
0.n
INTERNAL
DATA BUS
D
Q
Q
WRITE
ENABLE
READ
ENABLE
POWER
DOWN
READ
LATCH/PIN
PORT 2
General Purpose I/O
Devices which have internal program memory have the ability to use Port 2 for a general purpose I/O.
Data written to the port latch serves to set both level and direction of the data on the pin. When used as
an I/O port, it has complementary outputs that will drive both high and low logic levels. More detail on
the functions of these pins is provided under the description of output and input functions in this section.
Even if internal memory is present, the use of Port 2 as general purpose I/O pins is not recommended if
the device will be used to access external memory. This is because the state of the pins will be disturbed
during the memory access. It is still possible, however, to use the Port 2 latch to hold the upper address
byte for Register Indirect Addressing instructions.
Most Significant Address Byte, A8-15
When used to address expanded memory, Port 2 functions as the most significant byte of the address bus.
Port 2 must function as the address bus on ROMless devices. When serving as a bus, Port 2 will be
driven with strong drivers at all times except immediately after the rising edge of PSEN. See Figure 5-3
and 5-4 for more details.
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PORT 2 FUNCTIONAL CIRCUITRY Figure 10-2
ADDRESS
A8-A15
ADDRESS
CONTROL
VCC
DELAY
=2Tclk
VCC
PORT
0.n
INTERNAL
DATA BUS
D
Q
Q
VCC
WRITE
ENABLE
READ
ENABLE
POWER
DOWN
READ
LATCH/PIN
PORTS 1 AND 3
Ports 1 and 3 are general purpose I/O ports with optional special functions associated with each pin.
Enabling the special function automatically converts the I/O pin to that function. To insure proper
operation, each alternate function pin should be programmed to a logic 1. For example, enabling the
UART converts P3.0 and P3.1 to the serial I/O functions.
The drive characteristics of these pins do not change when the pin is configured for general I/O or as the
special function associated with that pin. The exceptions are pins P3.6 and P3.7, which employ the
current-limited transition drivers described later when used as RD and WR signals. The drive
characteristics of Port 1 and Port 3 are the same as for Port 2 (non-bus mode). That is, the logic 0 is
created by a strong pull-down. The logic 1 is created by a strong transition pull-up that changes to a weak
pull-up.
Using one or more I/O pins of a port as special function pins will not effect the remaining port pins. An
extreme example is as follows. P3.6 has the alternate function of WR and P3.7 of RD. These strobes are
used for expanded data memory access. If a system used only the RD signal, then P3.6 would still be
available as an I/O port. This is not a practical suggestion, but it illustrates how the special functions are
independent.
A more practical application is the optional use of an interrupt. If INT0 (P3.2) is enabled, then an
externally imposed logic 0 will cause an interrupt. By then disabling the INT0, P3.2 can be used as a
general purpose I/O pin. This allows the INT0 to be used to “wake-up” the system, but does not
eliminate another use of the pin.
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OUTPUT FUNCTIONS
Although 8051 I/O ports appear to be true I/O, their output characteristics are dependent on the individual
port and pin conditions. When software writes a logic 0 to the port for output, the port is pulled to
ground. When software writes a logic 1 to the port for output, Ports 1,2, or 3 will drive weak pull-ups
(after the strong transition from 0 to 1). Port 0 will go tri-state. Thus as long as the port is not heavily
loaded, true logic values will be output. DC drive capability is provided in the electrical specifications.
Note that the DC current available from an I/O port pin is a function of the permissible voltage drop.
Transition current is available to help move the port pin from a 0 to a 1. Since the logic 0 driver is strong,
no additional drive current is needed in the 1 to 0 direction. The transition current is applied when the
port latch is changed from a logic 0 to a logic 1. Simply writing a logic 1 where a 1 was already in place
does not change the strength of the pull-up. This transition current is applied for a one half of a machine
cycle. The absolute current is not guaranteed, but is approximately 2 mA at 5V.
When serving as an I/O port, the drive will vary as follows. For a logic 0, the port will invoke a strong
pull-down. For a logic 1, the port will invoke a strong pull-up for two oscillator cycles to assist with the
logic transition. Then, the port will revert to a weak pull-up. This weak pull-up will be maintained until
the port transitions from a 1 to a 0. The weak pull-up can be overdriven by external circuits. This allows
the output 1 state to serve as the input state as well.
Substantial DC current is available in both the high and low levels. However, the power dissipation
limitations make it inadvisable to heavily load multiple pins. In general, sink and source currents should
not exceed 10 mA total per port (8 bits) and 25 mA total per package.
CURRENT-LIMITED TRANSITIONS
The High-Speed Microcontroller family incorporates special circuitry to limit the current consumed by
the device when the expanded memory bus is used. These signals employ current-limited drivers which
“step” the transition from a logic 0 to a logic 1 to reduce ringing and electromagnetic interference. When
expanded memory operations are in progress, the following pins will exhibit the current-limiting feature:
Port 0
Port 2
PSEN (During program memory accesses)
ALE
RD (During data memory read cycles)
WR (During data memory write cycles)
INPUT FUNCTIONS
The input state of the I/O ports is the same as that of the output logic 1. That is, the pin is pulled weakly
to a logic 1. This 1 state is easily overcome by external components. Thus, after software writes a 1 to
the port pin, the port is configured for input. When the port is read by software, the state of the pin will
be read. The only exception is the read-modify-write instructions described below. If the external circuit
is driving a logic 1, then the pin will be a logic 1. If the external circuit is driving a 0, then it will
overcome the internal pull-up. Thus the pin will be the same as the driven logic state. Note that the port
latch is not altered by a read operation. Therefore, if a logic 0 is driven onto a port pin from an external
source, then removed, the pin will revert to the weak pull-up as determined by the internal latch.
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READ-MODIFY-WRITE INSTRUCTIONS
The normal read instructions will read the pin state without regard to the output data latch. The only
exception is the read-modify–write category of instructions. They are listed as follows.
INSTRUCTION DESCRIPTION
ANL
Logical AND
ORL
Logical OR
XRL
Logical Exclusive OR (XOR)
JBC
Branch if bit set then clear bit
CPL
Complement bit
INC
Increment
DEC
Decrement
DJNZ
Decrement and branch if not zero
MOV PX.n, C
Move the carry bit to bit n of port X
CLR PX.n
Clear bit n of port X
SETB PX.n
Set bit n of port X
The read-modify-write instructions read the state of the latch, then write back the result to the latch. Thus
the operation takes place using the value that was originally written to the SFR, without regard to the pin
state. The last three instructions listed above are read-modify-write because they read the entire port
latch, then write back the changed value. In this case, only one bit will be changed as specified by the
instruction.
I/O PORT TIMING
Figure 10-1 shows when port pins change in relationship to instruction timing. The example shown uses
a MOV command to change P1.0 from a logic 1 to a logic 0. This diagram is presented to aid the
designer in determining the timing relationship for very critical designs. Most designers will not need to
consider this much detail. Dummy NOP instructions are shown to illustrate subsequent instructions.
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I/O PORT TIMING FOR MOV INSTRUCTION Figure 10-1
Last Cycle of
Previous
Instr. & MOV
prefetch
C1
C2
C3
C4
C1
C2
C3
First NOP
Cycle &
Second NOP
prefetch
MOV Cycle 2
& First NOP
prefetch
MOV Cycle 1
C4
C1
C2
C3
C4
C1
C2
C3
C4
CLK
ALE
PSEN
P1.0
AD0-AD7
A0-A7
MOV
Opcode
Address
PORT 2
D0-D7
MOV
Instruction
Opcode
A0-A7
MOV
Operand
Address
A8-A15
D0-D7
MOV
Instruction
Operand
A0-A7
First NOP
Instruction
Address
A8-A15
D0-D7
A0-A7
D0-D7
Second NOP
Instruction
First NOP Address Second NOP
Instruction
Instruction
Opcode
Opcode
A8-A15
A8-A15
OPTIONAL FUNCTIONS
Every port pin on the High-Speed Microcontroller has an optional special function. These functions are
individually selectable. They can also be turned on and off dynamically to suit the application. The
optional function for each port pin is described briefly below. More information about each optional
function is available in the section dealing with that function or in the appropriate data sheet.
P0.0
P2.0
P0.1
P2.1
P0.2
P2.2
P0.3
P2.3
P0.4
P2.4
P0.5
P2.5
P0.6
P2.6
P0.7
P2.7
AD0.0 Multiplexed Address/data bus
A8 MSB Address bus
AD0.1 Multiplexed Address/data bus
A9 MSB Address bus
AD0.2 Multiplexed Address/data bus
A10 MSB Address bus
AD0.3 Multiplexed Address/data bus
A11 MSB Address bus
AD0.4 Multiplexed Address/data bus
A12 MSB Address bus
AD0.5 Multiplexed Address/data bus
A13 MSB Address bus
AD0.6 Multiplexed Address/data bus
A14 MSB Address bus
AD0.7 Multiplexed Address/data bus
A15 MSB Address bus
P1.0
P3.0
P1.1
P3.1
P1.2
P3.2
P1.3
P3.3
P1.4
P3.4
P1.5
P3.5
P1.6
P3.6
P1.7
P3.7
T2 Timer 2 output pulse
RXD0 Serial Receive UART0
T2EX Timer 2 capture/reload input
TXD0 Serial Transmit UART0
RXD1 Serial Receive UART1
INT0 External Interrupt 0 active low
TXD1 Serial Transmit UART1
INT1 External Interrupt 1 active low
INT2 External Interrupt 2 rising edge active
T0 Timer 0 input
INT3 External Int. 3 falling edge active
T1 Timer 1 input
INT4 External Interrupt 4 rising edge active
WR Write strobe
INT5 External Int. 5 falling edge active
RD Read strobe
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SECTION 11: PROGRAMMABLE TIMERS
All members of the High-Speed Microcontroller family incorporate three 16-bit programmable timers and
some also have a Watchdog Timer with a programmable interval. Because the Watchdog Timer is
significantly different from the other timers, it is described separately. The 16-bit Timers are referred to
simply as timers.
In most modes, the timers can be used as either counters of external events or timers. When functioning
as a counter, 1 to 0 transitions on a port pin are monitored and counted. When functioning as timers, they
effectively count oscillator cycles. The time base for the timer function is the main oscillator clock
divided by either 4 or 12. This selection is described below. Because each clock pulse must be sampled
high for one machine cycle and low for one machine cycle to be recognized, this sets the maximum
sampling frequency on any timer input at 1/8 of the main oscillator frequency.
The three timers are compatible with the 80C32. That is, they offer the same controls and I/O functions
that were available in the 80C32. As mentioned above, the actual timing of these functions is user
selectable to be compatible with the machine cycle of the older generation of 8051 family (12 clocks per
tick) or the new generation (4 clocks per tick). The timing for each of the three timers can be selected
independently and can be changed dynamically. Each timer has 4 primary modes as discussed below.
The Watchdog Timer Reset provides CPU monitoring by requiring software to clear the timer before the
user selected interval expires. If the Timer is not cleared, the CPU will be reset by the Watchdog. The
Watchdog function is optional and is described below. Since the High-Speed Microcontroller timers have
a variety of features, the following summary table shows the capabilities.
Timer 0
13–bit Timer/counter
16–bit Timer/counter
8–bit Timer w/ Auto–reload
Two 8–bit Timer/counters
External control pulse timer/counter
Timer 1
13–bit Timer/counter
16–bit Timer/counter
8–bit Timer w/ Auto–reload
External control pulse timer/counter
Baud rate generator
Timer 2
16–bit Timer/counter
16–bit Timer with capture
16–bit Auto–reload Timer/counter
16–bit up/down auto–reload
Timer/counter
Baud rate generator
Timer output clock generator
16-BIT TIMERS
Timers 0 and 1 are nearly identical. Timer 2 has several additional features such as up/down counting,
capture values and an optional output pin that make it unique. Timers 0 and 1 are described first. Timer
2 is described separately. As mentioned above, the time base for each timer can be varied and this is also
discussed in more detail below.
Timer 0 and 1 both have four operating modes. They are 13-bit timer/counter, 16-bit timer/counter, 8-bit
timer/counter with auto-reload, and two 8-bit timers. The latter mode is available to Timer 0 only. These
modes are controlled by the TMOD register. Each timer can also serve as a counter of external pulses (1
to 0 transition) on the corresponding Tn pin. This selection is controlled by the TMOD register. One
other option is to gate the timer/counter using an external control signal. This allows the timer to measure
the pulse width of external signals. Timers 0 and 1 are enabled using the TCON register which is also the
location of their flags. The registers are described below. Following this is a detailed explanation of the
four operating modes.
Each timer consists of a 16-bit register in two bytes. These are called TL0, TH0, TL1, and TH1. As
shown, each timer is broken into low and high bytes. Software can read or write any of these locations at
any time.
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TMOD REGISTER SUMMARY
TIMER MODE CONTROL
TMOD; 89h
TMOD.7
GATE - Timer 1 GATE control. When GATE=1, Timer 1 will
clock only when INT1 and TR1 =1. When GATE=0, Timer 1 will
clock only when TR1=1 irrespective of INT1 .
TMOD.6
C/ T - Counter/Timer select. When C/ T is set to a 0, Timer 1 is
incremented by internal clocks. When C/ T is set to a 1, Timer 1
counts based on the T1 (P3.5) pin.
TMOD.5
M1 - Timer 1 Mode select bit 1.
TMOD.4
M0 - Timer 1 Mode select bit 0.
M1
M0
Mode
0
0
Mode 0 : 8-bits with 5-bit prescale
0
1
Mode 1 : 16-bits
1
0
Mode 2 : 8-bits with auto-reload
1
1
Mode 3 : Timer 1 stopped
TMOD.3
GATE - Timer 0 GATE control. When GATE=1, Timer 0 will
clock only when INT0 and TR0 =1. When GATE=0, Timer 0 will
clock only when TR0=1 irrespective of INT0 .
TMOD.2
C/ T - Counter/Timer select. When C/ T is set to a 0, Timer 0 is
incremented by internal clocks. When C/ T is set to a 1, Timer 0
counts based on the T0 (P3.4) pin.
TMOD.1
M1 - Timer 0 Mode select bit 1.
TMOD.0
M0 - Timer 0 Mode select bit 0.
M1
M0
Mode
0
0
Mode 0 : 8-bits with 5-bit prescale
0
1
Mode 1 : 16-bits
1
0
Mode 2 : 8-bits with auto-reload
1
1
Mode 3 : Timer 0 is two 8-bit timers
TCON REGISTER SUMMARY
TIMER/COUNTER
CONTROL
TCON; 88h
TCON.7
TF1 - Timer 1 overflow flag. Set to one when Timer 1 overflows
from FFh, and cleared when the processor vectors to the interrupt
service routine.
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TCON.6
TR1 - Timer 1 run control. Turns on Timer 1 when this bit is set.
TCON.5
TF0 - Timer 0 overflow flag. Set to one when Timer 0 overflows
from FFh, and cleared when the processor vectors to the interrupt
service routine.
TCON.4
TR0 - Timer 0 run control. Turns on Timer 0 when this bit is set to
a one.
TCON.3
IE1 - Interrupt 1 edge detect. Set by hardware when an edge/level is
detected on INT1 .
TCON.2
IT1 - Interrupt 1 type select. INT1 detects a falling edge when this
bit is set to a 1. INT1 detects a low level when this bit is a 0.
TCON.1
IE0 - Interrupt 0 edge detect. Set by hardware when an edge/level is
detected on INT0 .
TCON.0
IT0 - Interrupt 0 type select. INT0 detects a falling edge when this
bit is set to a 1. INT0 detects a low level when this bit is a 0.
MODE 0
Mode 0 configures either Timer 0 or Timer 1 for operation as a 13-bit Timer/Counter. As shown in
Figure 11-1, bits M1=0 and M0=0 of the TMOD register select this operating mode.
When using Timer 0, TL0 uses only bits 0-4. These bits serve as the 5 LSbs of the 13-bit timer. TH0
provides the 8 MSbs of the 13-bit timer. Bit 4 of TL0 is used as a ripple out to TH0 bit 0, thereby
completely bypassing bits 5 through 7 of TL0. Once the timer is started using the TR0 (TCON.4) timer
enable, the timer will count as long as GATE (TMOD.3) is 0 or GATE is 1 and pin INT0 is 1. It will
count oscillator cycles if C/ T (TMOD.2) is set to a logic 0 and 1 to 0 transitions on T0 (P3.4) if C/ T is
set to a 1. When the 13-bit count reaches 1FFFh (all ones), the next count will cause it to roll over to
0000h. The TF0 (TCON.5) flag will be set and an interrupt will occur if enabled. The upper three bits of
TL0 will be indeterminate.
Note that when used as a timer, the time base may be either oscillator cycles/12 or oscillator cycles/4 as
selected by bits TnM (n=0 or 1) of the CKCON register. This feature is described in more detail below.
Mode 0 operates identically when Timer 1 is used. The same information applies to TL1 and TH1, which
form the 13-bit register. TR1 (TCON.6), INT1 (P3.3), T1 (P3.5), and the relevant C/T (TMOD.6) and
GATE (TMOD.7) bits have the same functions.
MODE 1
Mode 1 configures the timer for 16-bit operation as either a timer or counter. Figure 11-1 shows that bits
M1 = 0 and M0 = 1 of the TMOD register select this operating mode. For Timer n, all of the TLn and
THn registers are used. For example, if Timer 1 is configured in mode 1, then TL1 holds the LSB and
TH1 holds the MSB. Rollover occurs when the timer reaches FFFFh. An interrupt will also occur if
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enabled and the relevant TFn flag is set. Timebase selection, counter/timer selection, and the gate
function operate as described in mode 0.
TIMER/COUNTER 0 AND 1, MODES 0 AND 1 Figure 11-1
T0M = CKCON.3
(T1M = CKCON.4)
C/ T = TMOD.2
OSC INPUT TO TIMER
CLK MODE
TIMER INPUT
DIVIDE BY 4 OSC/1
PMM1
OSC/16
PMM2
OSC/256
T0 = P3.4
(T1 = P3.5)
DIVIDE
BY 12
(C/ T = TMOD.6)
0
0
DIVIDE
BY 4
CLK
0
TL0
(TL1)
7
4
1
00
1
01
TR0 = TCON.4
(TR1 = TCON.6)
0
GATE = TMOD.3
(GATE = TMOD.7)
TH0
(TH1)
MODE 0
M1, M0=TMOD.1,
TMOD.0
(M1, M0=TMOD.5,
TMOD.4)
MODE 1
7
INT0 = P3.2
TF0 = TCON.5
(TF1 = TCON.7)
( INT1 = P3.3)
TIMER 1 FUNCTIONS
SHOWN IN PARENTHESIS ()
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INTERRUPT
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MODE 2
This mode configures the timer as an 8-bit timer/ counter with automatic reload of the start value. This
configuration is shown in Figure 11-2, and is selected when bits M1and M0 of the TCON register are set
to 1 and 0 respectively. When configured in Mode 2, the timer uses TLn to count and THn to store the
reload value. Software must initialize both TLn and THn with the same starting value for the first count
to be correct. Once the TLn reaches FFh, it will be automatically loaded with the value in THn. The THn
value remains unchanged unless modified by software. Mode 2 is commonly used to generate baud rates
since it runs without continued software intervention. As in modes 0 and 1, mode 2 allows counting of
either oscillator cycles (crystal/12 or crystal/4) or pulses on pin Tn (C/T=1) when counting is enabled by
TRn and the proper setting of GATE and INTn pins.
TIMER/COUNTER 0 AND 1, MODE 2 Figure 11-2
T0M = CKCON.3
(T1M = CKCON.4)
OSC INPUT TO TIMER
CLK MODE
TIMER INPUT
DIVIDE BY 4 OSC/1
PMM1
OSC/16
2PMM2
OSC/256
T0 = P3.4
(T1 = P3.5)
DIVIDE
BY 12
(C/ T = TMOD.6)
0
0
DIVIDE
BY 4
C/ T = TMOD.2
CLK
TL0
(TL1)
0
7
RELOAD
1
1
TR0 = TCON.4
(TR1 = TCON.6)
0
GATE = TMOD.3
(GATE = TMOD.7)
TH0
(TH1)
7
INT0 = P3.2
TF0 = TCON.5
(TF1 = TCON.7)
( INT1 = P3.3)
INTERRUPT
TIMER 1 FUNCTIONS
SHOWN IN PARENTHESIS ()
MODE 3
This mode provides an 8-bit timer/counter and a second 8-bit timer as indicated in Figure 11-3. In Mode
3, TL0 is an 8-bit timer/counter controlled by the normal Timer 0 bits (TR0=TCON.4 and TF0=TCON.5).
TL0 can be used to count oscillator cycles (crystal/12 or crystal/ 4) or 1 to 0 transitions on pin T0 as
determined by C/ T (TMOD.2). As in the other modes, the GATE function can use INT0 to give external
run control of the timer to an outside signal.
TH0 becomes an independent 8-bit Timer in Mode 3, however it can only count oscillator cycles (divided
by 12 or 4) as shown in the figure. In this mode, some of Timer 1’s control signals are used to manipulate
TH0. That is, TR1 (TCON.6) and TF1 (TCON.7) become the relevant control and flag bits associated
with TH0.
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TIMER/COUNTER 0 MODE 3 Figure 11-3
OSC INPUT TO TIMER
CLK MODE
TIMER INPUT
DIVIDE BY 4 OSC/1
PMM1
OSC/16
PMM2
OSC/256
DIVIDE
BY 12
DIVIDE
BY 4
T0M = CKCON.3
0
C/ T = TMOD.2
0
CLK
0
1
TL0
7
1
T0 = P3.4
TF0 = TCON.5
INTERRUPT
TF1 = TCON.7
INTERRUPT
TR0 = TCON.4
GATE = TMOD.3
INT0 = P3.2
TR1 = TCON.6
0
TH0
7
In Mode 3, Timer 1 stops counting and holds its value. Thus Timer 1 has no practical application while
in Mode 3.
As mentioned above, when Timer 0 is in Mode 3, it uses some of Timer 1’s resources (i.e., TR1 and
TF1). Timer 1 can still be used in Modes 0, 1, and 2 in this situation, but its flexibility becomes
somewhat limited. While it maintains its basic functionality, its inputs and outputs are no longer
available. Therefore when Timer 0 is in Mode 3, Timer 1 can only count oscillator cycles, and it does not
have an interrupt or flag. With these limitations, baud rate generation is its most practical application, but
other time-base functions may be achieved by reading the registers.
TIMER 2
Like Timers 0 and 1, Timer 2 is a full function timer/ counter, however it has several additional
capabilities that make it more useful. Timer 2 has independent control registers in T2CON and T2MOD,
and is based on count registers TL2 and TH2. All of these registers are described in detail below.
T2CON REGISTER SUMMARY
TIMER TWO CONTROL
T2CON; C8h
T2CON.7
TF2 - Timer 2 Overflow Flag. Hardware will set TF2 when the
Timer 2 overflows from FFFFh or from the count equal to the
capture register in down count mode. It must be cleared to 0 by
software. TF2 will only be set to a 1 if RCLK and TCLK are both
cleared to a 0.
T2CON.6
EXF2 - Timer 2 External Flag. Hardware will set EXF2 when a
reload or capture is caused by a falling transition on the T2EX pin
(P1.1). EXEN2 must be set for this function. This flag must be
cleared to 0 by software. Writing a one to this bit will force a timer
interrupt if enabled.
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T2CON.5
RCLK - Receive Clock Flag. This bit determines whether Timer 1
or 2 is used for Serial Port 0 timing of received data in Serial Modes
1 or 3. RCLK = 1 causes Timer 2 overflow to be used as the receive
clock. RCLK = 0 causes Timer 1 overflow to be used as the receive
clock.
T2CON.4
TCLK - Transmit Clock Flag. This bit determines whether Timer 1
or 2 is used for Serial Port 0 timing of Transmit data in Serial
Modes 1 or 3. TCLK = 1 causes Timer 2 overflow to be used as the
transmit clock. TCLK = 0 causes Timer 1 overflow to be used as
the transmit clock.
T2CON.3
EXEN2 - Timer 2 External Enable. Setting this bit to a 1 allows a
capture or reload to occur as a result of a falling transition on T2EX
(P1.1), if Timer 2 is not generating baud rates for the serial port.
EXEN2 = 0 causes Timer 2 to ignore all external events at T2EX.
T2CON.2
TR2 - Timer 2 run. Setting this bit to a 1 starts Timer 2. Setting it
to a 0 stops Timer 2.
T2CON.1
C/ T2 - Counter/Timer Select. Setting this bit to a 0 selects a timer
function for Timer 2. Setting it to a 1 selects a counter of falling
transitions on T2 (P1.0). Timer 2 runs at 4 clocks per tick or 12
clocks per tick as programmed by CKCON.5. This bit will be
overridden and Timer 2 directed to use a divide by 2 clock if either
the baud–rate generator or clock output mode is used.
T2CON.0
CP/ RL2 - Capture/Reload Flag. When this bit is set to 1, Timer 2
captures will occur on 1 to 0 transitions of T2EX (P1.1) if EXEN2 =
1. When this bit is set to 0, auto–reloads will occur when Timer 2
overflows or when 1 to 0 transitions occur on T2EX if EXEN2 = 1.
If either RCLK or TCLK is set to a 1 this bit will not function and
the timer will function in an auto–reload mode following each
overflow.
T2MOD REGISTER SUMMARY
TIMER TWO MODE
CONTROL
T2MOD; C9h
T2MOD.7-2
Reserved
T2MOD.1
T2OE - Timer 2 Output Enable. Setting this bit to a 1 enables the
Timer 2 to drive the T2 (P1.0) pin with a clock output. When T2OE
= 0, the T2 (P1.0) pin is used as either an input for Timer 2 or a
standard port pin.
DCEN - Down Count Enable. When this bit is set to 1, the Timer 2
function counts up or down when in 16–bit auto–reload mode
depending on T2EX (P1.1). When DCEN is set to a 0, the Timer 2
counts up only.
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TIMER 2 CAPTURE REGISTERS SUMMARY
LEAST SIGNIFICANT
RCAP2L; CAh
BYTE CAPTURE OF TIMER 2
RCAP2L.7-0
This register is used to capture the TL2 value when Timer 2 is
configured in capture mode. RCAP2L is also used as the LSB of a
16-bit reload value when Timer 2 is configured in auto-reload mode.
MOST SIGNIFICANT
RCAP2H; CBh
BYTE CAPTURE OF TIMER 2
RCAP2H.7-0
This register is used to capture the TH2 value when Timer 2 is
configured in capture mode. RCAP2H is also used as the MSB of a
16-bit reload value when Timer 2 is configured in auto-reload mode.
TIMER 2 MODES
As is seen in the register descriptions, Timer 2 has several abilities not found in Timers 0 and 1.
However, it does not offer the 13-bit and dual 8-bit modes. Thus it runs in 16-bit mode at all times. Also
note that instead of offering an 8-bit auto-reload mode, Timer 2 has a 16-bit auto-reload mode. This
mode uses the Timer Capture registers to hold the reload values. The modes available on Timer 2 are
described below.
16-bit Timer/Counter
In this mode, Timer 2 performs a simple timer or counter function where it behaves similarly to mode 1
of Timers 0 and 1, but uses 16 instead of 8 bits. This mode, along with the optional capture mode
described below, is illustrated in Figure 11-4. The 16-bit count values are found in TL2 and TH2 Special
Function Registers (addresses 0CCh and 0CDh respectively). The selection of whether a Timer or
Counter function is performed is made using the bit C/ T2 (T2CON.1). When C/ T2 is set to a logic 1,
Timer 2 behaves as a counter where it counts 1 to 0 transitions at the T2 (P1.0) pin. When C/ T2 is set to
a logic 0, Timer 2 functions as a timer where it counts the oscillator cycles divided by either 12 or 4 as
determined by bit T2M (T2CON.5). Timing or counting is enabled by setting bit TR2 (T2CON.2) to 1,
and disabled by setting it to 0. When the counter rolls over from FFFFh to 0000h, the TF2 flag
(T2CON.7) is set and will cause an interrupt if Timer 2’s interrupt is enabled.
16-bit Timer with Capture
A diagram of Timer 2’s Capture Mode is shown in Figure 11-4. In this mode, the timer performs basically
the same 16-bit timer/counter function described above. However, a 1 to 0 transition on T2EX (pin P1.1)
causes the value in Timer 2 to be transferred into the capture registers if enabled by EXEN2 (T2CON.3).
The capture registers, RCAP2L and RCAP2H, correspond to TL2 and TH2 respectively. The capture
function is enabled by the CP/ RL2 (T2CON.0) bit. When set to a logic 1, the timer is in capture mode as
described. When set to a logic 0, the timer is in auto-reload mode described later. As was possible with
Timers 0 and 1, the timebase for Timer 2 may be selected to be oscillator cycles divided by either 12 or 4
when in this mode.
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TIMER/COUNTER 2 WITH OPTIONAL CAPTURE Figure 11-4
OSC INPUT TO TIMER
CLK MODE
TIMER INPUT
DIVIDE BY 4 OSC/1
PMM1
OSC/16
PMM2
OSC/256
DIVIDE
BY 12
DIVIDE
BY 4
T2M = CKCON.5
0
C/ T2 = T2CON.1
0 CLK
0
1
78
15
TL2
TH2
TF2 =
T2CON.7
1
T2 = P1.0
TR2 = T2CON.2
RCAP2H
RCAP2L
0
T2EX = P1.1
7
8
CAPTURE
15
TIMER 2
INTERRUPT
EXF2 =
T2CON.6
EXEN2 = T2CON.3
16-bit Auto-reload Timer/Counter
This mode is illustrated in Figure 11-5a. When Timer 2 reaches an overflow state, i.e., rolls over from
FFFFh to 0000, it will set the TF2 Flag. This flag can generate an interrupt if enabled. In addition, the
timer will restore its starting value and begin timing (or counting) again. The starting value is preloaded
by software into the capture registers RCAP2L and RCAP2H. These registers cannot be used for capture
functions while also performing auto-reload, so these modes are mutually exclusive. Auto-reload is
invoked by the CP/ RL2 (T2CON.0) bit. When set to a logic 0, the timer is in auto-reload mode. When
CP/ RL2 is set to a logic 1, the timer is in capture mode described above. If the oscillator timebase is used
(C/ T2 = T2CON.1 = 0), the timer’s input may be selected to be oscillator cycles divided by either 12 or 4
as determined by T2M (CKCON.5). Otherwise, pulses on pin T2 (P1.0) are counted when C/ T2 = 1. As
in other modes, Counting or timing is enabled or disabled with TR2 (T2CON.2).
When in auto-reload mode, Timer 2 can also be forced to reload with the T2EX (P1.1) pin. A 1 to 0
transition will force a reload if enabled by the EXEN2 (T2CON.3) bit. If EXEN2 is set to a logic 1, then
a 1 to 0 transition on T2EX will cause a reload. Otherwise, the T2EX pin will be ignored.
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TIMER/COUNTER 2 AUTO RELOAD MODE Figure 11-5
(a) DCEN = 0
OSC INPUT TO TIMER
CLK MODE
TIMER INPUT
DIVIDE BY 4 OSC/1
PMM1
OSC/16
PMM2
OSC/256
DIVIDE
BY 12
DIVIDE
BY 4
T2M = CKCON.5
0
C/ T2 = T2CON.1
0
CLK
0
1
78
15
TL2
TF2 =
T2CON.7
TH2
1
T2 = P1.0
TR2 = T2CON.2
RCAP2L
0
T2EX = P1.1
RCAP2H
78
15
TIMER 2
INTERRUPT
EXF2 =
T2CON.6
EXEN2 = T2CON.3
(b) DCEN = 1
OSC INPUT TO TIMER
CLK MODE
TIMER INPUT
DIVIDE BY 4 OSC/1
PMM1
OSC/16
PMM2
OSC/256
DIVIDE
BY 12
DIVIDE
BY 4
(DOWN COUNTING RELOAD VALUE)
0FFH
0FFH
T2M = CKCON.5
0
C/ T2 = T2CON.1
0
CLK
0
78
15
TL2
TH2
1
1
T2 = P1.0
TR2 = T2CON.2
T2EX = P1.1
0
COUNT DIRECTION
(1 = UP, 0 = DOWN)
78
RCAP2L
15
RCAP2H
(UP COUNTING RELOAD VALUE)
TF2 =
T2CON.7
TIMER 2
INTERRUPT
EXF2 =
T2CON.6
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High-Speed Microcontroller User’s Guide
Up/Down Count Auto–reload Timer/Counter
The up/down auto-reload counter option is selected by the DCEN (T2MOD.0) bit, and is illustrated in
Figure 11-5b. When DCEN is set to a logic 1, Timer 2 will count up or down as controlled by the state of
pin T2EX (P1.1). T2EX will cause upward counting when a logic 1 is applied and down counting when a
logic 0 is applied. When DCEN = 0, Timer 2 only counts up.
When an upward counting overflow occurs, the value in RCAP2L and RCAP2H will load into T2L and
T2H. In the down count direction, an underflow occurs when T2L and T2H match the values in RCAP2L
and RCAP2H respectively. When an underflow occurs, FFFFh is loaded into T2L and T2H and counting
continues.
Note that in this mode, the overflow/underflow output of the timer is provided to an edge detection circuit
as well as to the TF2 bit (T2CON.7). This edge detection circuit toggles the EXF2 bit (T2CON.6) on
every overflow or underflow. Therefore, the EXF2 bit behaves as a seventeenth bit of the counter, and
may be used as such.
Baud Rate Generator
Timer 2 can be used to generate baud rates for Serial Port 0 in serial modes 1 or 3. Baud rate generator
mode is invoked by setting either the RCLK or TCLK bit in the T2CON register to a logic 1, as illustrated
in Figure 116. In this mode, the timer continues to function in auto-reload mode, but instead of setting
the interrupt flag T2F (T2CON.7) and potentially causing an interrupt, the overflow generates the shift
clock for the serial port function. As in normal auto-reload mode, an overflow causes RCAP2L and
RCAP2H to be transferred into T2L and T2H respectively. Note that when RCLK or TCLK is set to 1,
the Timer 2 is forced into 16-bit auto-reload mode regardless of the CP/ RL2 bit.
As explained above, the timer itself cannot set the T2F interrupt flag and therefore cannot generate an
interrupt. However if EXEN2 (T2CON.3) is set to 1, a 1 to 0 transition on the T2EX (P1.1) pin will
cause the EXF2 (T2CON.6) interrupt flag to be set. If enabled, this will cause a Timer 2 Interrupt to
occur. Therefore in this mode, the T2EX pin may be used as an additional external interrupt if desired.
Another feature of the baud rate generator mode is that the crystal derived timebase for the timer is the
crystal frequency divided by 2. No other crystal divider selection is possible. If a different timebase is
desired, bit C/ T2 (T2CON.1) may be set to a 1 sourcing the timebase from an external clock source
supplied by the user on pin T2 (P1.0). Software should not access TL2 or TH2 while the timer is running
(TR2=1) in baud rate generator mode. In this mode the timer is clocking so fast that a software read of or
write to the TL2 and TH2 registers may corrupt the timer. The RCAP registers may be read, but not
modified, while TR2 = 1. Stop the timer (TR2 = 0) to modify these registers.
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High-Speed Microcontroller User’s Guide
TIMER/COUNTER 2 BAUD RATE GENERATOR MODE Figure 11-6
TIMER 1
OVERFLOW
OSC INPUT TO TIMER
CLK MODE
TIMER INPUT
DIVIDE BY 4 OSC/2
PMM1
OSC/82
PMM2
OSC/512
SMOD =
WDCON.7
DIVIDE
BY 2
C/ T2 = T2COD.1
0
0
CLK
1
T2 = P1.0
TR2 = T2CON.2
78
0
TL2
1
RCLK =
T2CON.5
15
TH2
1
0
TCLK =
T2CON.4
T2EX = P1.1
EXEN2 = T2CON.3
RCAP2L
0
RCAP2H
78
EXF2 =
T2CON.6
15
1
TIMER 2
INTERRUPT
DIVIDE
BY 16
0
Rx
CLOCK
DIVIDE
BY 16
Tx
CLOCK
Timer Output Clock Generator
Timer 2 can also be configured to drive a clock output on port pin P1.0 (T2) as shown in Figure 11-7. To
configure Timer 2 for this mode, first it must be set to 16-bit auto-reload timer mode (CP/ RL2 = 0,
C/ T2 = 0). Next, the T2OE (T2MOD.1) bit must be set to a logic 1. TR2 (T2CON.2) must also be set to
a logic 1 to enable the timer.
This mode will produce a 50% duty cycle square wave output. The frequency of the square wave is given
by the formula in the figure. Each timer overflow causes an edge transition on the pin, i.e., the state of
the pin toggles.
Note that this mode has two somewhat unique features in common with the baud rate generation mode.
First, the timebase is the crystal frequency divided by 2, and no other divider selection is possible.
Second, the timer itself will not generate an interrupt, but if needed, an additional external interrupt may
be caused using T2EX as described above. Because of the two mode’s similarities, the timer can be used
to generate both an external clock and a baud rate clock simultaneously. Once the clock out mode is
established, either TCLK or RCLK is set to 1, and the RCAP2 registers are loaded, the timer will provide
a clock to both functions.
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High-Speed Microcontroller User’s Guide
TIMER/COUNTER 2 CLOCK OUT MODE Figure 11-7
OSC INPUT TO TIMER
CLK MODE
TIMER INPUT
DIVIDE BY 4 OSC/2
PMM1
OSC/32
PMM2
OSC/512
F_OUT=
OSC INPUT
TO TIMER
(4*(65536RCAP2H,
RCAP2L))
C/T2 =
T2CON.1
=0
0
7 8
TL2
TR2 =
T2CON.2
0
T2 = P1.0
RCAP2L
7
15
TH2
8
RCAP2H
15
DIVIDE
BY 2
T2OE =
T2MOD.1
EXF2 =
T2CON.6
T2EX = P1.1
TIMER 2
INTERRUPT
EXEN2 = T2CON.3
TIME–BASE SELECTION
The High-Speed Microcontroller allows the user to select either 4 or 12 clocks as the time-base for each
timer independently. When using the 16-bit Timer/Counters in timer mode, the timer/counter counts the
oscillator cycles divided by a predetermined number. In the standard 8051, the 8051 timers count the
oscillator divided by 12, which is the standard 8051 machine cycle timing. The High-Speed
Microcontroller allows the option of setting the timers to operate from a divide by 4 of the input clock to
allow higher precision timing and faster baud rates. This selection has no effect on CPU timing, only on
the timers. Following a reset, the timers default to 12 clocks as the time-base to remain drop-in
compatible with the original 8051.
The 4 or 12 clock decision is independent for each timer and the default is 12 clocks per timer tick. As an
example, a user might select both the baud rate generator timer and one other timer to run at 12 clocks per
timer tick with the third timer at 4 clocks per tick. This allows one timer to measure higher speed events
or to gain better resolution. The control bits for the time-base selection are located in the Clock Control
register (CKCON;8Eh). Timer 2 will function at 2 clocks per tick when set for baud rate generation or
clock output as described above. When the time-base is derived from an external source (i.e., the T0, T1
or T2 pins), the timer operates at the frequency of the external source and is not affected by the setting of
the T0M, T1M, or T2M bits. The only limitation is that the external source frequency can be no faster
than 1/8 of the main oscillator frequency.
The use of Power Management modes will affect the input clock to the timer as shown in the illustrations.
In general, they will divide the input clock by either 16 or 256 for PMM1 and PMM2, respectively.
Timer 2, when operating in Baud Rate Generator or Clock Out mode normally uses the input clock
frequency divided by 2, but when PMM1 and PMM2 are used, it will operate from a time-base of the
input clock divided by 32 and 512, respectively.
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WATCHDOG TIMER
The Watchdog Timer is a user programmable clock counter that can serve as a time-base generator, an
event timer, or a system supervisor. As can be seen in the diagram of Figure 11-8, the timer is driven by
the main system clock that is supplied to a series of dividers. The divider output is selectable, and
determines the interval between time-outs. When the time-out is reached, an interrupt flag will be set,
and if enabled, a reset will occur. The interrupt flag will cause an interrupt to occur if its individual
enable bit is set and the global interrupt enable is set. The reset and interrupt are completely discrete
functions that may be acknowledged or ignored, together or separately for various applications.
WATCHDOG TIMER Figure 11-8
XTAL1
RWT (WDCON.0
(Reset Watchdog)
XTAL2
DIVIDE BY
1/16/256
DIVIDE BY
17
2
DIVIDE BY
3
2
DIVIDE BY
3
2
17
20
2
WD1 (CKCON.7)
WD0 (CKCON.6)
CLOCK DIVIDE CONTROL
CD1
CD0
DIVISOR
No PMR register
1
0
X
1
1
0
16
1
1
256
23
2
2
TIME-OUT
SELECTOR
DIVIDE BY
3
2
26
2
WDIF
(WDCON.3)
TIME-OUT
WATCHDOG
INTERRUPT
EWDI (EIE.4)
(Enable Watchdog
512 CLOCK
DELAY
EWT (WDCON.1)
(Enable Watchdog Timer
RESET
WTRF
(WDCON.2)
The Watchdog Timer Reset function works as follows. After initializing the correct time-out interval
(discussed below), software first restarts the Watchdog using RWT(WDCON.0) and then enables the
reset mode by setting the Enable Watchdog Timer Reset (EWT = WDCON.1) bit. At any time prior to
reaching its user selected terminal value, software can set the Reset Watchdog Timer (RWT =
WDCON.0) bit. If RWT is set before the time-out is reached, the timer will start over. If the time-out is
reached without RWT being set, the Watchdog will reset the CPU. Hardware will automatically clear
RWT after software sets it. When the reset occurs, the Watchdog Timer Reset Flag (WTRF =
WDCON.2) will automatically be set to indicate the cause of the reset, however software must clear this
bit manually.
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The Watchdog Timer is a free running timer. When used as a simple timer with both the reset and
interrupt functions disabled (EWT = 0 and EWDI = 0), the timer will continue to set the Watchdog
Interrupt flag each time the timer completes the selected timer interval as programmed by WD1
(CKCON.7) and WD0 (CKCON.6). Restarting the timer using the RWT (WDCON.0) bit, allows
software to use the timer in a polled time-out mode. The WDIF bit is cleared by software or any reset.
The Watchdog Interrupt is also available for applications that do not need a true Watchdog Reset but
simply a very long timer. The interrupt is enabled using the Enable Watchdog Timer Interrupt (EWDI =
EIE.4) bit. When the time-out occurs, the Watchdog Timer will set the WDIF bit (WDCON.3), and an
interrupt will occur if the global interrupt enable (EA = IE.7) is set. Note that WDIF is set 512 clocks
before a potential Watchdog Reset. The Watchdog Interrupt Flag will indicate the source of the interrupt,
and must be cleared by software.
Using the Watchdog Interrupt during software development can allow the user to select ideal watchdog
reset locations. Code is first developed without enabling the Watchdog Interrupt or Reset functions.
Once the program is complete, the Watchdog Interrupt function is enabled to identify the required
locations in code to set the RWT (WDCON.0) bit. Incrementally adding instructions to reset the
Watchdog Timer prior to each address location (identified by the Watchdog Interrupt) will allow the code
to eventually run without receiving a Watchdog Interrupt. At this point the Watchdog Timer Reset can be
enabled without the potential of generating unwanted resets. At the same time the Watchdog Interrupt
may also be disabled. Proper use of the Watchdog Interrupt with the Watchdog Reset allows interrupt
software to survey the system for errant conditions.
When using the Watchdog Timer as a system monitor, the Watchdog Reset function should be used. If
the Interrupt function were used, the purpose of the watchdog would be defeated. For example, assume
the system is executing errant code prior to the Watchdog Interrupt. The interrupt would temporarily
force the system back into control by vectoring the CPU to the interrupt service routine. Restarting the
Watchdog and exiting by an RETI or RET, would return the processor to the lost position prior to the
interrupt. By using the Watchdog Reset function, the processor is restarted from the beginning of the
program, and therefore placed into a known state.
The Watchdog has four time-out selections based on the input crystal frequency as shown in the figure.
The selections are a preselected number of clocks. Therefore, the actual time-out interval is dependent on
the crystal frequency. Shown below are the four time-outs with some example periods for different
crystal speeds. Note that the time period shown is for the interrupt event. The reset, when enabled, will
occur 512 clocks later regardless of whether the interrupt is used. Therefore the actual Watchdog timeout period is the number shown below plus 512 clocks. Watchdog generated resets will last for two
machine cycles.
WATCHDOG
NUMBER
OF
TIME AT
TIME AT
TIME AT
TIME AT
TIME AT
WD1
WD0
INTERVAL
CLOCKS
1.8432 MHz
11.0592 MHz
16 MHz
20 MHz
25 MHz
0
0
217
131072
71.11 ms
11.85 ms
8.19 ms
6.55 ms
5.24 ms
1
2
20
1048576
568.89 ms
94.81 ms
65.54 ms
52.43 ms
41.94 ms
2
23
8388608
4551.11 ms
758.52 ms
524.29 ms
419.43 ms
335.54 ms
2
26
67108864
36408.88 ms
6068.15 ms
4194.30 ms
3355.44 ms
2684.35 ms
0
1
1
0
1
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High-Speed Microcontroller User’s Guide
The Watchdog time-out selection is made using bits WD1 (CKCON.7) and WD0 (CKCON.6) as shown
in the figure. The time-out selections possible are shown in the bit descriptions that follow. The
watchdog timeout period is affected by the use of Power Management modes. The slower clock rate,
either divide by 64 or divide by 1024 is used as the input source for the watchdog timer. This allows the
watchdog period to remain synchronized with device operation.
As discussed above, the Watchdog Timer has several SFR bits that contribute to its operation. It can be
enabled to function as either a reset source, interrupt source, software polled timer or any combination of
the three. Both the reset and interrupt have status flags. The Watchdog also has a bit that restarts the
timer. A summary table showing the bit locations is below. A description follows.
BIT NAME
EWT
RWT
WD1
WD0
WTRF
EWDI
WDIF
DESCRIPTION
Enable Watchdog Timer Reset
Reset Watchdog Timer
Watchdog interval 1
Watchdog interval 0
Watchdog Timer Reset Flag
Enable Watchdog Timer Interrupt
Watchdog Interrupt Flag
REGISTER LOCATION
WDCON – D8h
WDCON – D8h
CKCON – 8Eh
CKCON – 8Eh
WDCON – D8h
EIE – E8h
WDCON – D8h
BIT POSITION
WDCON.1
WDCON.0
CKCON.7
CKCON.6
WDCON.2
EIE.4
WDCON.3
The Watchdog Timer is a free running timer. It will be disabled by a Power-fail Reset. A Watchdog
time-out reset will not disable the Watchdog Timer, but will restart the timer. In general, software should
set the Watchdog to whichever state is desired, just to be certain of its state. Control bits that support
Watchdog operation are described below.
WDCON REGISTER SUMMARY
WATCHDOG CONTROL
WDCON; D8h
WDCON.3
WDIF - Watchdog Interrupt Flag. If the Watchdog Interrupt is
enabled (EIE.4), hardware will set this bit to indicate that the
Watchdog Interrupt has occurred. If the interrupt is not enabled,
this bit indicates that the time-out has passed. If the Watchdog
Reset is enabled (WDCON.1), the user has 512 clocks to strobe the
Watchdog prior to a reset. Software or any reset can clear this flag.
WDCON.2
WTRF - Watchdog Timer Reset Flag. Hardware will set this bit
when the Watchdog Timer causes a reset. Software can read it, but
must clear it manually. A Power-fail Reset will also clear the bit.
This bit assists software in determining the cause of a reset. If
EWT=0, the Watchdog Timer will have no affect on this bit.
WDCON.1
EWT - Enable Watchdog Timer Reset. Setting this bit will turn on
the Watchdog Timer Reset function. The interrupt will not occur
unless the EWDI bit in the EIE register is set. A reset will occur
according to the WD1 and WD0 bits in the CKCON register.
Setting this bit to a 0 will disable the reset but leave the timer
running.
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High-Speed Microcontroller User’s Guide
WDCON.0
RWT - Reset Watchdog Timer. This bit serves as the strobe for the
Watchdog function. During the time-out period, software must set
the RWT bit if the Watchdog is enabled. Failing to set the RWT
will cause a reset when the time-out has elapsed. There is no need
to set the RWT bit to a 0 because it is self-clearing.
Read/write access:
All bits have unrestricted read access. POR, EWT, WDIF, and RWT require a
Timed Access write. The remaining bits have unrestricted write access.
CLOCK CONTROL
CKCON; 8Eh
CKCON.7
WD1 - Watchdog Timer mode select bit 1. See table below for
operation.
CKCON.6
WD0 - Watchdog Timer mode select bit 0. See table below for
operation. The WD select bits determine the time-out period of the
Watchdog Timer. The timer divides the crystal frequency by a
programmable value as shown below. The divider value is
expressed in number of clock (crystal) cycles. Note that the reset
time-out is 512 clocks longer than the interrupt, regardless of
whether the interrupt is enabled.
WD1
0
0
1
1
WD0
0
1
0
1
Interrupt
Divider
217
220
223
226
Reset
Divider
217 + 512
220 + 512
223 + 512
226 + 512
The default Watchdog time-out is the shortest one (WD1=WD0=0). Software can change this value
easily, so this should cause no inconvenience. However, the EWT, WDIF, and RWT bits are protected
under the Timed Access procedure. This prevents software from accidentally enabling or disabling the
Watchdog. Most importantly, it prevents errant code from accidentally clearing and restarting the
Watchdog. More details are discussed in the section on Timed Access.
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High-Speed Microcontroller User’s Guide
SECTION 12: SERIAL I/O
The High-Speed Microcontroller serial communication is compatible with the 80C32. This includes
framing error detection and automatic address recognition. The High-Speed Microcontroller provides
two fully independent UARTs (serial ports) for simultaneous communication over two channels. The
UARTs can be operated in identical or different modes and communication speeds. In this
documentation, all descriptions apply to both UARTs unless stated otherwise.
Each serial port is capable of both synchronous and asynchronous modes. In the synchronous mode, the
microcontroller generates the clock and operates in a half-duplex mode. In the asynchronous mode, full
duplex operation is available. Receive data is buffered in a holding register. This allows the UART to
receive an incoming word before software has read the previous value. Each UART has an associated
control register (SCON0, SCON1) and each has a transmit/receive register (SBUF0, SBUF1). The SFR
locations are: SCON0, 98h; SBUF0, 99h; SCON1, C0h; SBUF1, C1h. The SBUF location provides
access to both transmit and receive registers. Reads are directed to the receive buffer and writes to the
transmit buffer automatically.
SERIAL MODE SUMMARY
Each port provides four operating modes. These offer different communication protocols and baud rates.
These modes are summarized briefly as follows. Detailed descriptions are provided later in this section.
The use of Power management modes, if supported, will affect the internal clock rate and baud rate as
shown in Table 7-4. The following descriptions assume that Power Management modes are not in use.
MODE 0
This mode provides synchronous communication with external devices. It is commonly used to
communicate with serial peripherals. Serial I/O occurs on the RXD pin. The shift clock is provided on
the TXD pin. Note that whether transmitting or receiving, the serial clock is generated by the High-Speed
Microcontroller. Thus any device on the serial port in Mode 0 must accept the microcontroller as the
master.
The baud rate in Mode 0 is a function of the oscillator input. It will be the clock input divided by either
12 or 4. This is selected by the SM2 bit (SCON0.5 or SCON1.5) as described below. When set to a logic
0, the serial port runs at a divide by 12. When set to a logic 1, the serial port runs at a divide by 4. With
the exception of the additional new divide by 4 of the oscillator (supported by SM2), Mode 0 operation is
identical to the 80C32.
MODE 1
This mode provides standard full duplex asynchronous communication. A total of 10 bits is transmitted
including 1 start bit, 8 data bits, and 1 stop bit. The received stop bit is stored in bit location RB8 in the
relevant SCON register.
In Mode 1, the baud rate is a function of timer overflow. This makes the baud rate programmable by the
user. Mode 1 has a difference for the two UARTs. Serial Port 0 can use either Timer 1 or 2 to generate
baud rates. Serial Port 1 can use only Timer 1. Note that if both serial ports use the same timer, they will
be running at the same baud rate. If they use different timers (or different modes), they can run at
different rates. Baud rates are discussed in more detail below. Mode 1 operation is identical to the
standard 80C32 when Timers 1 or 2 use the default divide by 12 of the oscillator.
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High-Speed Microcontroller User’s Guide
MODE 2
This mode is an asynchronous mode that transmits a total of 11 bits. These include 1 start bit, 8 data bits,
a programmable ninth bit, and 1 stop bit. The ninth bit is determined by the value in TB8 (SCON0.3 or
SCON1.3) for transmission. When the ninth bit is received, it is stored in RB8 (SCON0.2 or SCON1.2).
The ninth bit can be a parity value by moving the P bit (PSW.0) to TB8.
The baud rate for Mode 2 is a function of the oscillator frequency. It is either the oscillator input divided
by 32 or 64 as programmed by the SMOD bit in the PCON register. Mode 2 operation is identical to the
standard 80C32.
MODE 3
This mode has the same functionality as Mode 2, but generates baud rates like Mode 1. That is, this mode
transmits 11 bits, but generates baud rates via the timers. Like Mode 1, either Timer 1 or 2 can be used
for Serial Port 0 and Timer 1 can be used for Serial Port 1. Mode 3 operation is identical to the standard
80C32 when Timers 1 or 2 use the default divide by 12 of the oscillator.
SERIAL PORT INITIALIZATION
In order to use the UART function(s), the serial port must be initialized. This involves selecting the mode
and time base, then initializing the baud rate generator if necessary. Serial communication is then
available. Once the baud rate generator is running, the UART can receive data.
In Mode 0, the High-Speed Microcontroller provides the clock. Serial reception is initiated by setting the
RI bit to a logic 0 and REN to a logic 1. This will generate a clock on the TXD pin and shift in the 8 bits
on the RXD pin. In the other modes, setting the REN bit to a logic 1 will allow serial reception. The
external device must actually initiate it by sending a start bit. In any mode, serial transmission is initiated
by writing to either the SBUF0 or SBUF1 location.
Most of the serial port controls are provided by the SCON0 and SCON1 registers. For convenience, these
are provided below. In addition, other control bits that influence the Serial Port operation are also
summarized below.
SERIAL I/O MODES
MODE
0
1
2
3
SYNCH/ASYNCH
Synch
Asynch
Asynch
Asynch
BAUD CLOCK†
4 or 12 tCLK
Timer 1 or 2*
32 or 64 tCLK
Timer 1 or 2*
DATA BITS
8
8
9
9
*Timer 2 available for Serial Port 0 only.
†The use of PMM1 or PMM2 will affect the baud clock.
139 of 175
START/STOP
None
1 start, 1 stop
1 start, 1 stop
1 start, 1 stop
9TH BIT FUNCTION
None
None
0, 1, parity
0, 1, parity
High-Speed Microcontroller User’s Guide
SERIAL PORT SCON0; 98h
CONTROL ZERO
This is the standard 80C32 Serial Port. The new Serial Port is designated Serial Port 1 and is documented
below.
SCON0.7
SM0/FE_0 - Serial Port 0 Mode bit 0 or Framing Error Flag.
PCON.6 (SMOD0) determines whether this bit functions as SM0 or
FE. The operation of SM0 (SMOD0 = 0) is described in the table
below. When SMOD0 = 1, the serial port will set FE to indicate an
invalid stop bit. When used as FE, this bit must be cleared in
software.
SCON0.6
SM1_0 - Serial Port 0 mode select 1. The operation of SM1 is
described in the table below. SCON0.5 SM2_0 - Multiple MCU
communication. Setting this bit to a one enables multiprocessor
communication in Modes 2 or 3. If the ninth bit is 0, the RI_0 will
not be set. In Mode 1, setting the SM2_0 bit to a one causes the
RI_0 bit not to be set if a valid stop bit is not received. In the HighSpeed Microcontroller, SM2_0 also has a new function. In mode 0,
the SM2_0 bit controls whether the serial port clock runs at a divide
by 4 or a divide by 12 of the oscillator when not in PMM. When set
to a logic 0, the serial port runs at a divide by 12. When set to a
logic one, the serial port runs at a divide by 4. This results in much
faster synchronous serial communication.
SCON0.4
REN_0 - Receive Enable. When set to a 1, the receive shift register
will be enabled.
SCON0.3
TB8_0 - Set/clear to define the state of the ninth transmission data
bit in modes 2 and 3.
SCON0.2
RB8_0 - Indicates the state of an incoming ninth bit when in modes
2 and 3. In mode 1, when SM2 =0, RB8_0 is the state of the stop
bit received. RB8_0 is not used in mode 0. SCON0.1 TI_0 - Flag
that indicates the transmitted word has been completely shifted out.
In mode 0, TI_0 is set at the end of the eighth data bit. In all other
modes, this bit is set at the end of the last data bit. It must be cleared
manually by software.
SCON0.0
RI_0 - Flag that indicates a serial word has been received. In mode
0, RI_0 is set at the end of the eighth bit. In mode 1, it is set after the
last sample of the incoming stop bit subject to the state of SM2_0.
In modes 2 and 3, RI_0 is set after the last sample of RB8_0. It must
be cleared manually by software.
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SM0/FE_0 SM1_0
Mode Function
Length
0
0
0
Sync
8 bits
0
1
1
1
0
1
1
2
3
Asynch
Asynch
Asynch
10 bits
11 bits
11 bits
Initialization:
SCON is set to 00h on a reset.
Read/Write Access:
Unrestricted.
SERIAL PORT
CONTROL ONE
SCON1; C0h
Period
4/12 tCL
(see SM2)
Timer 1 or 2
64/32 tCLK
Timer 1 or 2
Serial Port 1 performs identically to the standard Serial Port 0 on an 80C32 with one exception. The baud
rate generation from Timer 2 is not available in Modes 1 and 3. Timer 1 is used. The port is located at
P1.3 and P1.2 for TXD1 and RXD1 respectively.
SCON1.7
SM0/FE_1 - Serial Port 1 Mode bit 0 or Framing Error Flag.
PCON.6 (SMOD0) determines whether this bit functions as SM0 or
FE. The operation of SM0 (SMOD0 = 0) is described in the table
below. When SMOD0 = 1, the serial port will set FE to indicate an
invalid stop bit. When used as FE, this bit must be cleared in
software.
SCON1.6
SM1_1 - Serial Port 1 mode select 1. The operation of SM1_1 is
described in the table below.
SCON1.5
SM2_1 - Multiple MCU communication. Setting this bit to a one
enables multiprocessor communication in Modes 2 or 3. If the ninth
bit is 0, the RI_1 will not be set. In Mode 1, setting the SM2_1 bit
to a one causes the RI_1 bit not to be set if a valid stop bit is not
received. In the High-Speed Microcontroller, SM2_1 also has a
new function. In mode 0, the SM2_1 bit controls whether the serial
port clock runs at a divide by 4 or a divide by 12 of the oscillator
when not in PMM. When set to a logic 0, the serial port runs at a
divide by 12. When set to a logic one, the serial port runs at a divide
by 4. This results in much faster synchronous serial communication.
REN_1 - Receive Enable. When set to a 1, the receive shift register
will be enabled.
SCON1.4
SCON1.3
TB8_1 - Set/clear to define the state of the ninth transmission data
bit in modes 2 and 3.
SCON1.2
RB8_1 - Indicates the state of an incoming ninth bit when in modes
2 and 3. In mode 1, when SM2 = 0, RB8 is the state of the stop bit
received. RB8 is not used in mode 0.
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SCON1.1
TI_1 - Flag that indicates the transmitted word has been completely
shifted out. In mode 0, TI is set at the end of the eighth data bit. In
all other modes, this bit is set at the end of the last data bit. It must
be cleared manually by software.
SCON1.0
RI_1 - Flag that indicates a serial word has been received. In mode
0, RI_1 is set at the end of the eighth bit. In mode 1, it is set after the
last sample of the incoming stop bit subject to the state of SM2_1.
In modes 2 and 3, RI_1 is set after the last sample of RB8_1. It must
be cleared manually by software.
SM0
SM1
Mode
Function
Length
0
0
0
Sync
8 bits
0
1
1
1
0
1
1
2
3
Asynch
Asynch
Asynch
10 bits
11 bits
11 bits
Period
4/12 tCLK
(see SM2)
Timer 1
64/32 tCLK
Timer 1
Initialization:
SCON1 is set to 00h on a reset.
Read/Write Access:
Unrestricted.
POWER CONTROL
PCON; 87h
PCON.7
SMOD_0. - Doubles the serial baud rate in modes 1, 2, and 3 for
Serial Port 0 (the standard port) when SMOD = 1.
PCON.6
SMOD0 - Framing Error Detection Enable. When SMOD0 is set to a one,
SCON0.7 and SCON1.7 are converted to the FE flag for the respective serial port.
When SMOD0 is 0, then SCON0.7 and SCON1.7 are the SM0 function as
defined for the serial port.
WATCHDOG CONTROL
WDCON; D8h
WDCON.7
SMOD_1 - Serial Modification. When set to a logic 1, this bit
doubles the baud rate of Serial Port 1. It works identically to
PCON.7.
TIMER TWO CONTROL
T2CON; C8h
T2CON.5
RCLK - Receive Clock Flag. This bit determines whether Timer 1
or 2 is used for Serial Port 0 timing of received data in Serial Modes
1 or 3. RCLK = 1 causes Timer 2 overflow to be used as the receive
clock. RCLK = 0 causes Timer 1 overflow to be used as the receive
clock.
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T2CON.4
TCLK - Transmit Clock Flag. This bit determines whether Timer 1
or 2 is used for Serial Port 0 timing of Transmit data in Serial
Modes 1 or 3. TCLK = 1 causes Timer 2 overflow to be used as the
transmit clock. TCLK = 0 causes Timer 1 overflow to be used as
the transmit clock.
BAUD RATES
Each mode has a baud rate generator associated with it. This generator is generally the same for each
UART. Several of the baud rate generation techniques have options and these options are independent
for the two UARTs. The baud rate descriptions given below are separated by mode.
Mode 0
Baud rates for this mode are driven directly from the crystal speed divided by either 12 or 4. Mode 0 is
synchronous so that the shift clock output frequency will be the baud rate. The formula is simply as
follows:
Mode 0 baud rate =
Oscillator Frequency
12
Mode 0 baud rate =
Oscillator Frequency
4
or
The default case is divide by 12. The user can select the using the SM2 bit in the associated SCON
register. For Serial Port 0, the SM2_0 bit is SCON0.5. For Serial Port 1, the SM2_0 bit is SCON1.5.
When SM2 is set to a logic 0, the baud rate is generated using a divide by 12 of the oscillator input.
When SM2 is set to a logic 1, the baud rate is generated using divide by 4. Note that this use of SM2
differs from a standard 80C32. In that device, SM2 had no valid use when the UART was in Mode 0.
Since it was generally set to a 0, for the divide by 12, there is no compatibility problem.
Mode 2
In this asynchronous mode, baud rates are also generated from the oscillator input. This mode works
identically to the original 8051 family. The baud rate is given by the following formula.
2 SMOD_x
Oscillator Frequency
*
Mode 1, 3 baud rate =
64
12 * (256 - TH1)
The result of this formula generates a baud rate of either1/32 * oscillator frequency or 1/64 * oscillator
frequency. In the formula, the numerator is expressed as two to the power of SMOD, where SMOD is
either a 0 or 1. When 0, the numerator is a 1 and when SMOD = 1, the numerator is a 2.
SMOD is a bit that effectively doubles the baud rate when set to a logic 1. For Serial Port 0, SMOD_0
resides at PCON.7. This is the original location in the 8051 family. For Serial port 1, SMOD_1 resides
in WDCON.7. The SMOD bits are set to a logic 0 on reset, which gives the lower speed baud rate.
If the application determines that Mode 0 or 2 must be used, then the oscillator or crystal frequency must
be selected to generate the correct baud rates since each mode offers two selections for a given frequency.
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Mode 1 or 3
These asynchronous modes are commonly used for communication with PCs, modems, and other similar
interfaces. The baud rates are programmable using the oscillator input and 16-bit Timer 2 or 8-bit Timer
1. The respective timer is placed in auto-reload mode. Each time the timer reaches its rollover condition
(FFFFh -Timer 2 or FFh - Timer 1), a clock is sent to the baud rate circuit. This clock is then divided by
16 to generate the exact baud rate. For Serial Port 0, either Timer 1 or 2 can be used to generate baud
rates. Note that there are difdivider regisferences between the timers when used as baud rate generators.
Serial Port 1 can use Timer 1 as a baud rate generator. Thus in Mode 1 or 3, the two serial ports can
run at the same frequency if Timer 1 is used for both, but different frequencies if both timers are used.
Also note that the user can determine the speed at which Timer 1 runs (4 clocks or 12 clocks). In most
cases, 12 clocks will be used for baud rate generation. Timer 2 runs from a 2 clock scheme when used for
baud rate generation. This is compatible with the 80C32.
The baud rates for Mode 1 or 3 are given by these formulas.
Serial Port 0 or 1
2 SMOD_x
*
Mode 1, 3 baud rate =
32
Timer 1 Overflow
Serial Port 0
Timer 2 Overflow
Mode 1, 3 baud rate =
16
To use Timer 1 as the baud rate generator, it is commonly put into the 8-bit auto-reload mode. In this
way, the CPU is not involved in baud rate generation. Note that the timer interrupt should not be enabled.
In the 8-bit auto-reload mode (Timer 1 Mode 2), the reload value is stored in TH1. Thus the combination
of crystal frequency and TH1 determine the baud rate. The complete formula is as follows.
2 SMOD_x
Oscillator Frequency
*
Mode 1, 3 baud rate =
32
12 * (256 - TH1)
Note that the 12 in the denominator can be changed to a 4 as determined by the Timer selection (T1M;
CKCON.4). This formula provides the derived baud rate for a given TH1 and crystal. Most users already
know what baud rate is desired and want the timer reload value. Thus the equation solves as follows,
when T1M=0.
TH1 = 256 -
2 SMOD_x * Oscillator Frequency
32* Baud Rate
Note that the most common application is to use Timer 1 in 8-bit auto-reload mode as a timer. It can
actually be used in any mode and can also be configured as a counter.
To use Timer 2 as baud rate generator for Serial Port 0, the Timer is configured in auto-reload mode.
Then either TCLK or RCLK bit (or both) are set to a logic 1. TCLK = 1 selects Timer 2 as the baud rate
generator for the transmitter and RCLK = 1 selects Timer 2 for the Thus Serial Port 0 can have the
transmit and receive operating at different baud rates by choosing 1 for one data direction and Timer 2 for
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the other. Setting either RCLK or TCLK to a logic 1 selects Timer 2 for baud rate generation. RCLK
and TCLK reside in T2CON.4 and TCON.5 respectively.
When using Timer 2 to generate baud rates, the formula will be as follows. Note that the reload value is a
16-bit number as compared with Timer 1, which uses only 8 bits.
o
Mode 1, 3 baud rate =
OscillatorFrequency
32 * (65536 − RCAP2H, RCAP2L)
Note that the 32 in the denominator is a result of the timer being run at a divide by 2, combined with the
divide by 16 applied to timer overflows as mentioned above. Timer 2 normally runs at a divide by either
12 or 4 in auto-reload mode. Setting RCLK or TCLK causes the divide by 2 operation.
This formula provides the derived baud rate for a given RCAP2H, RCAP2L and crystal. Most users
already know what baud rate is desired and want the timer reload value. Thus the equation solves as
follows.
RCAP2H, RCAP2L = 65536 –
OscillatorFrequency
32 * BaudRate
The Timer 2 interrupt is automatically disabled when either RCLK or TCLK is set. Also, the TF2
(TCON.7) flag will not be set on a timer rollover. The manual reload pin, T2EX (P1.1), will not cause a
reload either.
SERIAL I/O DESCRIPTION
A detailed description of each serial mode is given below. A description of framing error detection and
multiprocessor communication follows this section.
Mode 0
This mode is used to communicate in synchronous, half–duplex format with devices that accept the HighSpeed Microcontroller as a master. A functional block diagram and basic timing of this mode are shown
in Figure 12-1. As can be seen, there is one bidirectional data line (RXD) and one shift clock line (TXD)
used for communication. The shift clock is used to shift data into and out of the microcontroller and the
remote device. Mode 0 requires that the microcontroller is the master because the microcontroller
generates the serial shift clocks for both directions. As described above, the shift clock may be selected
to be either divide by 12 or divide by 4 of the oscillator as determined by the SM2 (SCON0.5 or
SCON1.5) bit.
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SERIAL PORT MODE 0 Figure 12-1
SBUF
OUTPUT SHIFT REGISTER
LOAD
CLOCK
OSC
DIVIDE
BY 12
0
P3.0
LATCH
RXD
PIN
D7
D6
D5
D4
D3
D2
D1
D0
S0
DIVIDE
BY 4
1
SM2=
SM2=
SCONx.5
SCONx.5
DATA BUS
LDSBUF
RECEIVE
BUFFER
LOAD
DATA
CLOCK
SI
T1
FLAG =
SCONx.1
RECEIVE DATA BUFFER WR
RD
D7
D6
D5
D4
D3
D2
D1
D0
INTS
BAUD
CLOCK
SHIFT
READ
SERIAL
BUFFER
CLOCK
LOAD
SERIAL
BUFFER
SERIAL I/O
CONTROL
RDSBUF
RECEIVE SHIFT REGISTER
R1
FLAG =
SCONx.0
SERIAL
INTERRUPT
TXD
PIN
TRANSMIT TIMING
LDSBUF
SHIFT
RXD
(DATA OUT)
TXD
(DATA CLOCK)
WRITE TO SBUF
D0
D1
D2
D3
D4
D5
D6
D7
TI
RECEIVE TIMING
RDSBUF
SHIFT
RXD
(DATA IN)
TXD
(DATA CLOCK)
WRITE TO SCON (CLEAR RI)
D0
D1
RI
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D3
D4
D5
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D7
High-Speed Microcontroller User’s Guide
The RXD signal is used for both transmission and reception. TXD provides the shift clock. Data bits
enter and exit LSb first. The baud rate is equal to the shift clock frequency. This can be either oscillator
divided by 4 or oscillator divided by 12. The relevant UART will begin transmitting when any
instruction writes to SBUF0 or SBUF1 (hex address 99 or C1). The internal shift register will then begin
to shift data out. The clock will be activated and will transfer data until the 8-bit value is complete. Data
will be presented one oscillator cycle prior to the falling edge of the shift clock (TXD), and an external
device can latch the data using the rising edge.
The UART will begin to receive data when the REN bit in the SCON register (SCON0.4 or SCON1.4) is
set to a logic 1 and the RI bit (SCON0.0 SCON1.0) is set to a logic 0. This condition tells the UART that
there is data to be shifted in. The shift clock (TXD) will activate and the UART will latch incoming data
on the rising edge. The external device should therefore present data on the falling edge. This process
will continue until 8 bits have been received. The RI bit will automatically be set to a logic 1, one
machine cycle following the last rising edge of the shift clock on TXD. This will cause reception to stop
until the SBUF has been read, and the RI bit cleared. When RI is cleared, another byte will be shifted in.
Mode 1
This mode is asynchronous, full duplex, using a total of 10 bits. The 10 bits consist of a start bit (logic 0),
8 data bits, and 1 stop bit (logic 1) as illustrated in Figure 12-2. The data is transferred LSb first. As
described above, the baud rates for Mode 1 are generated by either a divide by 16 of Timer 1 rollover, a
divide by 16 of the Timer 2 rollover, or a divide by 16 of (Timer 1 rollover)/2. The UART will begin
transmission 5 oscillator cycles after the first rollover of the divide by 16 counter following a software
write to SBUF. Transmission takes place on the TXD pin. It begins by the start bit being placed on the
pin. Data is then shifted out onto the pin, LSb first. The stop bit follows. The TI bit is set two oscillator
cycles after the stop bit is placed on the pin. All bits are shifted out at the rate determined by the baud
rate generator.
Once the baud rate generator is active, reception can begin at any time. The REN bit (SCON0.4 or
SCON1.4) must be set to a logic 1 to allow reception. The falling edge of a start bit on the RXD pin will
begin the reception process. Data will be shifted in at the selected baud rate. At the middle of the stop bit
time, certain conditions must be met to load SBUF with the received data:
1. RI must = 0, and either
2. If SM2 = 0, the state of the stop bit doesn’t matter, or
3. If SM2 = 1, the state of the stop bit must=1.
If these conditions are true, then SBUF (hex address 99h or C1h) will be loaded with the received byte,
the RB8 bit (SCON0.2 or SCON1.2) will be loaded with the stop bit, and the RI bit (SCON0.0 or
SCON1.0) will be set. If these conditions are false, then the received data will be lost (SBUF and RB8
not loaded) and RI will not be set. Regardless of the receive word status, after the middle of the stop bit
time, the receiver will go back to looking for a 1 to 0 transition on the RXD pin.
Each data bit received is sampled on the 7th, 8th and 9th clock used by the divide by 16 counter. Using
majority voting, two equal samples out of the three, determines the logic level for each received bit. If
the start bit was determined to be invalid (=1), then the receiver goes back to looking for a 1 to 0
transition on the RXD pin in order to start the reception of data.
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Mode 2
This mode uses a total of 11 bits in asynchronous full duplex communication as illustrated in Figure 12-3.
The 11 bits consist of one start bit (a logic 0), 8 data bits, a programmable 9th bit, and one stop bit (a
logic 1). Like Mode 1, the transmissions occur on the TXD signal pin and receptions on RXD. For
transmission purposes, the 9th bit can be stuffed as a logic 0 or 1. A common use is to put the parity bit in
this location. The 9th bit is transferred from the TB8 bit position in the SCON register (SCON0.3 or
SCON1.3) during the write to SBUF. Baud rates are generated as a fixed function of the crystal
frequency as described above. Like Mode 1, Mode 2’s transmission begins 5 oscillator cycles after the
first rollover of the divide by 16 counter following a software write to SBUF. It begins by the start bit
being placed on the TXD pin. The data is then shifted out onto the pin LSb first, followed by the 9th bit,
and finally the stop bit. The TI bit (SCON0.1 or SCON1.1) is set when the stop bit is placed on the pin.
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SERIAL PORT MODE 1 Figure 12-2
SMOD_0=
PCON.7
OR
SMOD_1=
WDCON.7
0
1
TCLK =
T2CON.4
RCLK =
T2CON.5
0
1
STOP
D7
D6
D5
D4
D3
D2
D1
D0
START
LOAD
0
P3.1
LATCH
S0
TXD
PIN
DATA BUS
LDSBUF
RDSBUF
LOAD
SERIAL
BUFFER
DIVIDE
BY 16
0
1
BAUD
CLOCK
1
SHIFT
SERIAL I/O
CONTROL
DIVIDE
BY 2
AVAILABLE TO SERIAL
PORT 0 ONLY
TIMER 2
OVERFLOW
TIMER 1
OVERFLOW
CLOCK
SBUF
TRANSMIT SHIFT REGISTER
SBUF
READ
SERIAL
BUFFER
RECEIVE DATA BUFFER
RD
WR
LOAD
RESET
D4
D3
D2
D1
D0
START
SI
SERIAL
INTERRUPT
D7
D6
D5
R1
FLAG =
SCONx.0
CLOCK
T1
FLAG =
SCONx.1
STOP
INTS
RB8=
SCONx.2
RECEIVE SHIFT REGISTER
DIVIDE
BY
16
RXD
PIN
BIT
DETECTION
TRANSMIT TIMING
LDSBUF
SHIFT
TXD
START
D0
D1
D2
D3
D4
D5
D6
D7
STOP
TI
RECEIVE TIMING
RXD
START
D0
D1
D2
BIT DETECTOR
SAMPLING
SHIFT
RI
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D3
D4
D5
D6
D7
STOP
High-Speed Microcontroller User’s Guide
SERIAL PORT MODE 2 Figure 12-3
1
P3.1
LATCH
S0
D7
D6
D5
D4
D3
D2
D1
D0
START
LOAD
OSC/2=
CRYSTAL/2
CLOCK
STOP
D8
SBUF
TRANSMIT SHIFT REGISTER
TXD
PIN
0
DIVIDE
BY 2
SMOD_0=
PCON.7
OR
SMOD_1=
WDCON.7
0
TB8 =
SCONx.3
1
DATA BUS
LDSBUF
RDSBUF
SHIFT
DIVIDE
BY 16
SHIFT
CLOCK
SBUF
READ
SERIAL
BUFFER
SERIAL I/O
CONTROL
LOAD
SERIAL
BUFFER
RECEIVE DATA BUFFER WR
RD
LOAD
RESET
D4
D3
D2
D1
D0
START
SI
SERIAL
INTERRUPT
D8
D7
D6
D5
R1
FLAG =
SCONx.0
STOP
T1
FLAG =
SCONx.1
CLOCK
INTS
RB8=
SCONx.2
RECEIVE SHIFT REGISTER
DIVIDE
BY
16
RXD
PIN
BIT
DETECTION
TRANSMIT TIMING
LDSBUF
SHIFT
TXD
START
D0
D1
D2
D3
D4
D5
D6
D7
TB8
STOP
TI
RECEIVE TIMING
RXD
START
D0
D1
D2
BIT DETECTOR
SAMPLING
SHIFT
RI
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High-Speed Microcontroller User’s Guide
Reception begins when a falling edge is detected as part of the incoming start bit on the RXD pin. The
RXD pin is then sampled according to the baud rate speed. The 9th bit is placed in the RB8 bit location in
SCON (SCON0.2 or SCON1.2). When a stop bit has been received, the data value will be transferred to
the SBUF receive register (hex address 99 or C1). The RI bit (SCON0.0 or SCON1.0) will be set to
indicate that a byte has been received. At this time, the UART can receive another byte.
Once the baud rate generator is active, reception can begin at any time. The REN bit (SCON0.4 or
SCON1.4) must be set to a logic 1 to allow reception. The falling edge of a start bit on the RXD pin will
begin the reception process. Data must be shifted in at the selected baud rate. At the middle of the 9th bit
time, certain conditions must be met to load SBUF with the received data.
1. RI must = 0, and either
2. If SM2 = 0, the state of the 9th bit doesn’t matter, or
3. If SM2 = 1, the state of the 9th bit must = 1.
If these conditions are true, then SBUF will be loaded with the received byte, RB8 will be loaded with the
9th bit, and RI will be set. If these conditions are false, then the received data will be lost (SBUF and RB8
not loaded) and RI will not be set. Regardless of the receive word status, after the middle of the stop bit
time, the receiver will go back to looking for a 1 to 0 transition on RXD.
Data is sampled in a similar fashion to Mode 1 with the majority voting on three consecutive samples.
Mode 2 uses the sample divide by 16 counter with either the oscillator divided by 2 or 4.
Mode 3
This mode has the same operation as Mode 2, except for the baud rate source. As shown in Figure 12-4,
Mode 3 can use Timer 1 or 2 for Serial Port 0 and Timer 1 for Serial Port 1. The bit shifting and protocol
are the same.
FRAMING ERROR DETECTION
A framing error occurs when a valid stop bit is not detected. This results in the possible improper
reception of the serial word. The UART can detect a framing error and notify the software. Typical
causes of framing errors are noise and contention. The Framing Error condition is reported in the SCON
register for the corresponding UART.
The Framing Error bit, FE, is located in SCON0.7 or SCON1.7. Note that this bit normally serves as
SM0 and is described as SM0/FE_0 or SM0/FE_1 in the register description. Framing Error information
is made accessible by the Framing Error Detection Enable bit. It is SMOD0 located at PCON.6. When
SMOD0 is set to a logic 1, the framing error information is shown in SM0/FE (SCON0.7 or SCON1.7).
When SMOD0 is set to a logic 0, the SM0 function is accessible. The information for bits SM0 and FE is
actually stored in different registers. Changing SMOD0 only changes which register is accessed; not the
contents of either.
The FE bit will be set to a 1 when a framing error occurs. It must be cleared by software. Note that the
SMOD0 state must be 1 while reading or writing the FE bit. Also note that receiving a properly framed
serial word will not clear the FE bit. This must be done in software.
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SERIAL PORT MODE 3 Figure 12-4
SMOD_0=
PCON.7
OR
SMOD_1=
WDCON.7
0
TCLK =
T2CON.4
RCLK =
T2CON.5
1
0
1
TXD
PIN
0
TB8=
SCONx.3
DATA BUS
LDSBUF
RDSBUF
LOAD
SERIAL
BUFFER
DIVIDE
BY 16
0
P3.1
LATCH
S0
D4
D3
D2
D1
D0
START
LOAD
1
BAUD
CLOCK
1
SHIFT
SERIAL I/O
CONTROL
DIVIDE
BY 2
AVAILABLE TO SERIAL
PORT 0 ONLY
TIMER 2
OVERFLOW
TIMER 1
OVERFLOW
CLOCK
STOP
D8
D7
D6
D5
SBUF
TRANSMIT SHIFT REGISTER
SBUF
READ
SERIAL
BUFFER
RECEIVE DATA BUFFER
RD
WR
LOAD
RESET
SI
SERIAL
INTERRUPT
D4
D3
D2
D1
D0
START
R1
FLAG =
SCONx.0
STOP
D8
D7
D6
D5
T1
FLAG =
SCONx.1
CLOCK
INTS
RB8=
SCONx.3
RECEIVE SHIFT REGISTER
DIVIDE
BY
16
RXD
PIN
BIT
DETECTION
TRANSMIT TIMING
LDSBUF
SHIFT
TXD
START
D0
D1
D2
D3
D4
D5
D6
D7
TB8
STOP
TI
RECEIVE TIMING
RXD
START
D0
D1
D2
D3
BIT DETECTOR
SAMPLING
SHIFT
RI
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D4
D5
D6
D7
RB8
STOP
High-Speed Microcontroller User’s Guide
MULTIPROCESSOR COMMUNICATION
Multiprocessor communication mode makes special use of the 9th data bit in Modes 2 and 3. In the
original 8051, the 9th bit was restricted to a 0 or 1 condition, but had no special purpose. In the 80C32
and the High-Speed Microcontroller, it can be used to signify that the incoming byte is an address. This
allows the processor to be interrupted only if the correct address appears. The receive interrupt, if
enabled, will only occur when a recognized address is received.
When a serial word is received with the 9th bit set and the appropriate smz=1, the byte will be assumed to
be an address. The address will be compared to an internally stored address. If it matches, a receive
interrupt will occur. The internal address is derived from the contents of two registers. The first register
specifies an absolute address. This is the user specified address of the device. The second register tells
the comparator which address bit(s) to actually use in the comparison. This allows broadcast
transmissions that reach groups of microcontrollers or all microcontrollers on a serial port. The user
defines this protocol.
There are two Special Function Registers that support multiprocessor communication for each UART.
These are independent, so that different addresses can be used in each. The registers are SADDR0 or
SADDR1(hex address A9h or AAh) and SADEN0 or SADEN1 (hex address B9h or BAh). The SADDR
register specifies the individual processor’s address. The SADEN identifies address bits that should be
ignored in matching addresses.
Software will write an 8-bit address to the SADDR register. This is the microcontroller’s individual
address. Any bit in SADEN that contains a logic 0 will cause the corresponding bit in SADDR to be
ignored in comparison. Thus logic 0 bits in SADEN create don’t care bit states for address comparisons.
When an address is received, each address bit that is not masked by a don’t care will be compared to the
SADDR. The microcontroller will interrupt on any address that matches this comparison. Any address
that meets this comparison is called a Given Address. The following example shows how one address
can be directed to an individual processor, or two out of three.
Micro 1
SADDR 11110000
SADEN 11111010
–––––––––––––––––––––––––
Given 11110x0x
Micro 2
SADDR 11110001
SADEN 11111001
–––––––––––––––––––––––––
Given 11110xx1
Micro 3
SADDR 11110010
SADEN 11111010
–––––––––––––––––––––––––
Given 11110x1x
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Note that an address of 11110000 will reach only microcontroller 1. An address of 11110001 will reach
both microcontroller 1 and microcontroller 2. An address of 11110010 will reach only microcontroller 3.
The microcontroller will also match on any address that corresponds to the Broadcast Address. This is
the logical OR of the SADDR and SADEN registers, with any 0s defined as don’t cares. In most cases,
the Broadcast Address will be FFh.
The multiprocessor communication is always enabled. However, the SADEN registers default to 00h,
which means all address bits are don’t care, so all match. Thus if no multiprocessor communication is
used, these registers can be ignored.
The Timer 2 interrupt is automatically disabled when either RCLK or TCLK is set. Also, the TF2
(TCON.7) flag will not be set on a timer rollover. The manual reload pin, T2EX (P1.1), will not cause a
reload either.
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High-Speed Microcontroller User’s Guide
SECTION 13: TIMED ACCESS PROTECTION
The High-Speed Microcontroller uses a protection feature called Timed Access to prevent accidental
writes to critical SFR bits. These bits could cause a system failure or prevent the Watchdog Timer from
doing its job if improperly written. The Timed Access involves opening a timing window during which
the protected bit can be modified. If the window is opened correctly, it remains open long enough to alter
one protected bit. This section explains which bits are protected, why, and how to use the Timed Access
feature.
PROTECTED BITS
Bits which are protected by the Timed Access feature are shown below. Only critical function bits which
are unique to the High-Speed Microcontroller family are protected, assuring code compatibility with the
original 80C51 or 80C52. A full description of the function of each bit is provided in Section 4.
EXIF.0
WDCON.6
WDCON.1
WDCON.0
WDCON.3
TRIM.7
TRIM.6
TRIM.5
TRIM.4
TRIM.3
TRIM.2
TRIM.1
TRIM.0
ROMSIZE.2
ROMSIZE.1
ROMSIZE.0
RTCC.2
RTCC.0
BGS
POR
EWT
RWT
WDIF
E4K
X12/ 6
TRM2
Band-gap Select
Power-on Reset Flag
Watchdog Reset Enable
Reset Watchdog Timer
Watchdog Interrupt Flag
4096 Hz RTC Output
12pF/6pF Crystal Select
Capacitance Trim Bit 2
TRM2
Inverse Capacitance Trim Bit 2
TRM1
Capacitance Trim Bit 1
TRM1
Inverse Capacitance Trim Bit 1
TRM0
Capacitance Trim Bit 0
TRM0
Inverse Capacitance Trim Bit 0
RMS2
ROM Size Select Bit 2
RMS1
ROM Size Select Bit 1
RMS0
ROM Size Select Bit 0
RTCWE RTC Write Enable
RTCE
RTC Enable
PROTECTION SCHEME
Each bit mentioned above is protected against an accidental write by requiring the software to perform a
procedure before writing the bit. Timed Access requires the software to write two specific values to the
Timed Access register during two consecutive instruction cycles. The values AAh, then 55h, must be
written in consecutive instructions to the TA register at SFR location C7h. If the writes are performed
correctly, the write access window will open for three machine cycles. During this window, the software
may modify a protected bit. The suggested code to open a Timed Access window is:
MOV 0C7h, #0AAh
MOV 0C7h, #55h
The procedure to modify a Timed Access protected bit begins by writing the value AAh to the Time
Access register (TA;C7h). The value 55h must then be written to the Timed Access register within three
machine cycles of writing AAh. This opens a three machine cycle window, after the write of 55h, during
which any Timed Access protected bits may be modified. Failure to complete any of the required steps
will also require the procedure to begin again, starting with the write of AAh to the Timed Access
register. Attempts to modify Timed Access protected bits after the window has closed will be ignored.
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This is regardless of whether any bits were modified. Figure 13-1 illustrates a number of examples of
correct and incorrect use of the Timed Access procedure.
TIMED ACCESS EXAMPLES Figure 13-1
three machine cycles
three machine cycles
MOV 0C7h, #0AAh
MOV 0C7h, #55h
three machine cycles
three machine cycles
MOV 0C7h, #0AAh
three machine cycles
SETB EWT
one machine cycle
MOV 0C7h, #55h
NOP
three machine cycles
three machine cycles
three machine cycles
MOV 0C7h, #0AAh
MOV 0C7h, #55h
MOV WDCON, #02h
two machine cycles
SETB EWT
VALID TIMED ACCESS PROCEDURES
three machine cycles
MOV 0C7h, #0AAh
one machine cycles
NOP
three machine cycle
MOV 0C7h, #55H
two machine cycles
SETB EWT
*Second write to TA register does not occur within 3 cycles of first write.
three machine cycles
MOV 0C7h, #0AAh
three machine cycles
one machine cycle
MOV 0C7h, #55H
NOP
three machine cycles
MOV WDCON, #02h
*Modification of protected bit did not occur with 3 cycles of second write to TA register.
three machine cycles
MOV 0C7h, #0AAh
three machine cycles
two machine cycle
MOV 0C7h, #55h
SETB EWT
two machine cycles
SETB EWT
*Modification of second protected bit did not complete within 3 cycles of second write to TA register.
INVALID TIMED ACCESS PROCEDURES
TIMED ACCESS PROTECTS WATCHDOG
Any microcontroller-based system can be faced with environmental conditions that are beyond its
designed abilities. These include external signal transients due to component failure, fluctuating power
conditions, massive electrostatic discharge (ESD), and other unexpected system events. When a
microcontroller is exposed to such conditions, program execution can become corrupted. Members of the
High-Speed Microcontroller family which incorporate a Watchdog Timer can initiate a reset to recover
from these conditions. The primary function of the Timed Access feature is to protect against accidental
disabling of the watchdog timer by an “out-of-control” device. This will allow the watchdog timer to
reset the system in the event of program execution failure.
The following hypothetical example demonstrates how a single bit change can corrupt program
execution. The Timed Access procedure protects against an accidental write to the EWT bit by the errant
code, allowing the watchdog timer reset function to reset the device. While this is a purely fictitious
example, it illustrates how the watchdog timer and Timed Access feature make the High-Speed
Microcontroller minimize the effect of accidental code corruption. Note: Timed Access is not optional
and must be supported if the protected bits are used. This example simply helps explain the category of
problem that the Timed Access prevents.
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High-Speed Microcontroller User’s Guide
EXAMPLE: A TRANSIENT CAUSES THE WATCHDOG TO BE DISABLED
TABLE_READ:
C2D2 90 0A 00
MOV
DPTR, 0A00H
;LOAD TABLE POINTER
C2D5 79 FF
MOV
R1, #0FFH
;LOAD COUNTER
C2D7 78 90
MOV
R0, #90H
;DESTINATION POINTER
C2D9
C2DA
C2DB
C2DC
C2DD
E0
F6
06
A3
D9 C2 D9
LOOP:
MOVX
MOV
INC
INC
DJNZ
A, @DPTR
@R0, A
R0
DPTR
R1, LOOP
;READ DATA BYTE
;STORE IT IN RAM
;NEXT TABLE LOCATION
;NEXT DATA VALUE
;NEXT BYTE OR DONE ?
A transient occurs while the opcode is being fetched for the first instruction. The transient causes one bit
of the opcode in the first instruction to be read as a 0 instead of 1. The resulting program is what the
microcontroller would actually execute:
TABLE_READ:
C2D2 80 0A 00
C2D5 79 FF
C2D7 78 90
SJMP
MOV
MOV
0BH
R1, #0FFH
R0, #90H
;RELATIVE JUMP BY 10 LOCATIONS
;LOAD COUNTER
;DESTINATION POINTER
C2D9
C2DA
C2DB
C2DC
C2DD
LOOP:
MOVX
MOV
INC
INC
DJNZ
A, @DPTR
@R0, A
R0
DPTR
R1, LOOP
;READ DATA BYTE
;STORE IT IN RAM
;NEXT TABLE LOCATION
;NEXT DATA VALUE
;NEXT BYTE OR DONE ?
E0
F6
06
A3
D9 C2 D9
The resulting jump is to address C2DE. This is not even a real opcode, but would be treated as such. The
resulting fetch is the value C2 D9. This is the opcode for CLR D9h. The bit addressable location D9h
corresponds to the EWT - Enable Watchdog Timer. If the Timed Access procedure did not prevent it,
this errant instruction would disable the Watchdog. Note that now, the program execution is completely
lost. Real opcodes are being replaced by operands, data and garbage. In the High-Speed Microcontroller,
the Watchdog will recover from this state as soon as it times out since it could not have been disabled in
this way.
In the High-Speed Microcontroller it is very hard to contrive a situation that will accidentally disable the
Watchdog. Note, the Timed Access prevents accidentally writing a bit. It can not prevent accidentally
calling the correct code that writes a bit. This is much more unlikely however.
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High-Speed Microcontroller User’s Guide
SECTION 14: REAL-TIME CLOCK
The DS87C530 incorporates a real-time clock (RTC) onto the High-Speed Microcontroller family core.
This allows the device to perform real-time related functions such as data logging and time-stamping
without an external timer. In addition, the RTC includes an alarm function which can execute a software
interrupt or resume operation from Stop mode at a specified time. The RTC features are controlled by 12
new SFRs. These registers, as well as two new interrupt control bits are shown in Table 14-1.
REAL-TIME CLOCK CONTROL AND STATUS BIT SUMMARY Table 14-1
BIT NAME
ERTCI
PRTCI
RTASS.7–0
RTAS.5–0
RTAM.5–0
RTAH.4–0
RTCSS.7–0
LOCATION
EIE.5
EIP.5
RTASS
RTAS
RTAM
RTAH
RTCSS
FUNCTION
RTC Interrupt Enable
RTC Interrupt Priority
RTC Alarm Subsecond
RTC Alarm Second
RTC Alarm Minute
RTC Alarm Hour
RTC Subsecond
RANGE
0–FFh
0–3Bh
0–3Bh
0–17H
0–FFh
RESET
0
0
Unchanged
Unchanged
Unchanged
Unchanged
Unchanged
RTCS.5–0
RTCM.5–0
RTCH.4–0
DOW.2–0
RTCD1.7–0
RTCD0.7–0
SRCE
RTCS
RTCM
RTCH.4–0
RTCH.7–5
RTCD1, (MSB)
RTCD0, (LSB)
RTCC.7
RTC Second
RTC Minute
RTC Hour
RTC Day of Week
RTC Day
0–3Bh
0–3Bh
0–17h
0–7h
0–FFFFh
Unchanged
Unchanged
Unchanged
Unchanged
Unchanged
Read: only if RTCRE=1.
Write: only if RTCWE=1.
1.95 ms Read/Write window
Unchanged
Unrestricted
SCE
RTCC.6
Unchanged
Unrestricted
MCE
RTCC.5
Unchanged
Unrestricted
HCE
RTCC.4
Unchanged
Unrestricted
RTCRE
RTCWE
RTCC.3
RTCC.2
RTC Subsecond
Compare Enable
RTC Second Compare
Enable
RTC Minute Compare
Enable
RTC Hour Compare
Enable
RTC Read Enable
RTC Write Enable
RTCIF
RTCE
E4K
RTCC.1
RTCC.0
TRIM.7
Unchanged
Unchanged
0
X12/6
TRIM.6
TRM2–0
TRIM.5
TRIM.3
TRIM.1
RTC Interrupt Flag
RTC Enable
External 4096 Hz RTC
Signal Enable
RTC Crystal Capacitance Select
RTC Trim Bit 2–0
0
0
READ/WRITE ACCESS
Unrestricted
Unrestricted
Unrestricted
Unrestricted
Unrestricted
Unrestricted
Read: only if RTCRE=1.
Cannot be written. Cleared
when RTCWE 1–>0
Unrestricted
Read: Unrestricted
Write: Timed Access
Unrestricted
Read: Unrestricted
Write: Timed Access
Unchanged
Unchanged
Read: Unrestricted
Write: Timed Access
The RTC control and status registers can be subdivided into 4 groups: RTC time registers (RTCSS;FAh,
RTCS;FBh, RTCM;FCh, RTCH;FDh, RTCD0;FEh, RTCD1;FFh), RTC alarm registers (RTASS;F2h,
RTAS;F3h, RTAM;F4h, RTAH;F5h), RTC calibration (TRIM;96h), and RTC control (RTCC;F9h).
STARTING AND STOPPING THE RTC
Operation of the RTC is enabled by setting the RTC Enable bit, RTCE (RTCC.0) to 1. This will start the
RTC crystal amplifier, and begin clocking the RTC. Like all crystal oscillators, the RTC crystal oscillator
has a crystal warm-up period. Software should allow a minimum of 1 second between setting the RTCE
bit to 1 and initializing the time. This allows the clock to be guaranteed stable when timekeeping begins.
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Although it may be desired to program the RTC time registers and then start the oscillator, this sequence
is not recommended because of the delay incurred by the RTC crystal warm-up period.
There are two situations where the RTC will be started. The first is the case where the RTC has been
intentionally halted following normal operation. When the RTCE bit is set, the time registers will
continue their count from the last setting when the clock was stopped. The RTC time value will be
inaccurate, although the settings of the RTC alarm registers and the RTCC register will remain intact.
The second case is following the application of battery power. Most of the registers associated with the
RTC are non-volatile, so that they will maintain their state while VCC is removed. When battery power is
applied to the device, however, the battery backed registers and bits associated with the RTC will be in an
indeterminate state and will need to be reinitialized. This includes the RTC Interrupt Flag, RTCIF
(RTCC.1), which should be cleared before setting the RTC Interrupt Enable bit (EIE.5).
The RTC can be halted by clearing the RTCE bit to 0. This will immediately halt the RTC and will
freeze all the time registers at their current value and preserve all the RTC settings. If RTC functions are
not desired, this can be used to reduce the power consumption of the device while in battery backed
mode.
SETTING AND READING THE RTC TIME REGISTERS
Access to the RTC time registers (RTCSS, RTCS, RTCM, RTCH, RTCD0, RTCD1) is enabled by the
RTCRE (RTCC.3) and RTCWE (RTCC.2) bits. Both user software and the internal clock directly write
and read the RTC time. To prevent the possibility of both user software and the internal timer accessing
the same register simultaneously, the DS87C530 incorporates a register locking mechanism. Updates to
the RTC time registers by the internal timer are temporarily suspended for up to 1.95 ms during software
read or write operations. If a subsecond timer tick should occur during the 1.95 ms window, it will be
processed immediately as soon as either the RTCWE or RTCRE bit is cleared. Because the subsecond
timer tick interval is 3.906 ms, the 1.95 ms window allows sufficient time to complete any operations and
process suspended timer ticks before the next timer tick occurs. In this way, no timer ticks can be lost,
and accessing the time registers will not affect the accuracy of the RTC. To allow any pending timer
ticks to propagate through the RTC circuitry, software must wait 4 machine cycles after setting the
RTCWE or RTCRE bits before accessing any of the RTC time registers. The first timer tick following
the clearing of the RTWCE bit will be approximately 1.95 ms. All following timer ticks will be 3.90625
ms.
Reading the current time from any or all of the RTC time registers is accomplished by the following
procedure:
1.
2.
3.
4.
5.
6.
Disable all interrupts by clearing the EA bit (IE.7),
Set the RTCRE bit (RTCC.3),
Wait 4 machine cycles,
Read the appropriate register(s) within 1 ms of RTCRE being set,
Clear the RTCRE bit (RTCC.3),
Enable interrupts by setting the EA bit (IE.7).
The time on the DS87C530 is set by writing to the Clock Registers. The Second, Minute, Hour, Day of
the Week, and Day Count can be set by writing to the respective registers. It is not possible to set the
Subsecond Real Time Clock Register (RTCS; FAh). This register is automatically reset to 00h when the
RTCWE bit is cleared, either through software or the automatic time-out of the 1.95 ms write window.
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Writing an invalid time to these registers (loading the RTCM register with 3Dh or 61 minutes, for
example) will result in an inaccurate count by the RTC. It is the responsibility of the software to ensure
that only valid times are written to these registers.
The procedure for setting an RTC time register is as follows:
1.
2.
3.
4.
5.
6.
7.
8.
Disable all interrupts by clearing the EA bit (IE.7),
Perform a Timed Access procedure,
Set the RTCWE bit (RTCC.2),
Wait 4 machine cycles,
Write the appropriate register(s) within 1.95 ms of RTCWE being set,
Perform a Timed Access procedure,
Clear the RTCWE bit (RTCC.2),
Enable interrupts by setting the EA bit (IE.7).
USING THE RTC ALARM
The RTC alarm function is used to generate an interrupt when the RTC value matches selected alarm
register values. An alarm can be triggered by a match on one or more of the following alarm registers:
Subsecond (RTASS;F2h), Second (RTAS; F3h), Minute (RTAM; F4h), and Hour (RTAH; F5h). Note
that there is no alarm register associated with the RTC Day Count or Day of Week registers. If an alarm
is desired on a specific date, an alarm can be executed once a day and user software can compare the
current date against the Day Register. It is not necessary to set the RTC Write Enable bit, RTCWE, when
setting the alarm registers.
The alarm can be set to occur on a match with any or all of the alarm registers. An alarm can occur on a
unique time of day, or a recurring alarm can be programmed every subsecond, second, minute, or hour.
Alarms can occur synchronously, when the clock rolls over to match the alarm condition, or
asynchronously, if the alarm registers are set to a value that matches the current time. Note that only one
alarm may occur per subsecond tick. This means that if a synchronous alarm has already occurred during
the current subsecond, software cannot cause an asynchronous alarm in the same subsecond.
The specific alarm registers to be compared are selected by setting or clearing the corresponding compare
enable bits (RTCC.7-4). Any compare bit which is cleared will result in that register being treated as a
Don’t Care when evaluating alarm conditions. Clearing all the compare enable bits will disable the
ability of the RTC to cause an interrupt, and will immediately clear the RTC Interrupt Flag (RTCC.1).
Unlike some interrupts, the RTC flag is not cleared by exiting the RTC interrupt service routine and must
be explicitly cleared in software.
The general procedure for setting the RTC alarm registers to cause a RTC interrupt is as follows:
1.
2.
3.
4.
5.
Clear the ERTCI Enable bit (EIE.5),
Clear all RTC Alarm Compare enable bits (ANL RTCC, #0Fh),
Write one or more RTC Alarm registers,
Set the desired RTC Alarm Compare enable bits,
Set the ERTCI Enable bit (EIE.5).
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Setting the alarm to cause an interrupt once during a 24-hour period is done by setting all the alarm
registers to the desired value and enabling all compare bits. A recurring alarm is enabled by clearing the
compare enable bits associated with one or more alarm registers. For example, to specify an alarm to
occur once a minute, the SSCE and SCE bits would be set. In general, a recurring alarm is set using the
next lower time increment than the desired interrupt period. For example, if an alarm was desired once an
hour, on the hour, a compare on the Real Time Alarm Minute Register would be performed, because the
Real Time Clock Minute Register will match the corresponding alarm register only once an hour. The
RTASS, RTAS, and RTAM registers would be cleared to 00h, and the SSCE, SCE, and MCE bits would
all be set to 1 to match on the time xx:00:00:00. Writing an invalid time to these registers (loading the
RTAM register with 3Dh or 61 minutes, for example) will never cause a match by the RTC. It is the
responsibility of the software to ensure that only valid times are written to these registers.
It is important to remember that any RTC register whose corresponding compare enable bit is cleared to 0
will always be treated as a match. The alarm registers are interrogated once per subsecond tick to check
for an alarm condition. If the SSCE bit was set to a don’t care (cleared to 0) in the above example, a
match (and interrupt) would occur during every subsecond of the minute in which the Real Time Alarm
Minute register matched.
If an alarm occurs while in data retention state (VCC < VBAT ), the RTCIF flag will be set and the interrupt
will remain pending. When power is reapplied to the device, the device will execute an RTC interrupt as
soon as interrupts are enabled.
USING THE DAY OF THE WEEK BITS
The DS87C530 contains 3 Day of the Week bits, DOW.2-0 located in the upper 3 bits of the Real Time
Clock Hour register (RTCH;FDh). These allow the processor to count from 1 to 7. The day of the week
bits will increment anytime the hour register changes from 17h to 00h, indicating a new day. When the
day of the week register reaches a count of 111b, it will roll over to 001b.
If the day of the week feature is not needed, writing 000b to the bits will disable the ability of an hour
register rollover to change the day of the week. The bits will remain at 000b. This is very convenient
from a software standpoint, as it is not necessary to zero out the high order bits when determining the
hour from the RTC Hour register.
CHOOSING AN RTC CRYSTAL
The RTC clock source is provided by an external 32.768 kHz crystal attached to the RTCX1 and RTCX2
leads of the DS87C530. The device can be programmed to operate with a crystal rated for either a 6 pF
or 12.5 pF load capacitance. The crystal selection is determined by the RTC Crystal Capacitance Select
bit (TRIM.6). The default state of this bit after a no–battery reset is for a 12.5 pF crystal.
In general, a lower capacitance crystal will consume less power, but will be more susceptible to noise.
Unlike the processor crystal inputs (X1, X2), the RTC crystal does not require external load capacitors.
Placing load capacitors on the RTC crystal input pins will cause the RTC to keep incorrect time. To
prevent system noise from affecting the RTC, the RTCX1 and RTCX2 pins should be guard-ringed with
the GND2 signal.
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CALIBRATING THE RTC OSCILLATOR
Although the DS87C530 RTC accuracy is guaranteed for ± 2 minutes per month, users may occasionally
require greater accuracy. The RTC incorporates the ability to adjust the internal capacitance of the crystal
amplifier via the RTC Trim Bits (TRM2-0 and TRM2 - 0 ). This allows the user to more accurately match
the capacitance of the crystal amplifier to the crystal. Note that under most circumstances no adjustment
of the RTC crystal capacitance is necessary, as it will default to a minimum accuracy of ± 2 minutes per
month.
All of the crystal capacitance controls are located in the RTC Trim register (TRIM;96h). Setting the E4K
bit will enable the output of a 4096 Hz signal on P1.7. This signal is derived from a divide by 8 of the
32.768 kHz crystal. Because this is directly generated from the RTC, it can be used to determine the
actual frequency of the RTC. By adjusting the value of the TRMx bits, the internal capacitance of the
RTC can be varied, slightly slowing or speeding up the RTC frequency. The combination of TRMx bits
(TRIM.5–0) that causes the output on pin P1.7 to most closely approximate 4096 Hz will provide the
most accurate setting of RTC capacitance.
As a precaution against accidental corruption of the oscillator trim bit settings, the TRMx bits must be
programmed in the same instruction to the inverse of their respective TRMx bits. For example, if a trim
bit setting of 5 (101) was desired, the TRMx bits should be set to 2 (010). An illegal combination will
automatically reset the TRIM register to 0x100101b. This will disable the E4K signal on P1.7, but leave
the X12/6 bit unmodified.
More information on calibrating the RTC oscillator for improved accuracy is located in Application Note
79, Using the DS87C530 Real Time Clock.
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SECTION 15: BATTERY BACKUP
The DS87C530 incorporates a feature which can maintain timekeeping and on-chip SRAM contents in
the absence of VCC. An external energy source such as a lithium battery or 0.47 F super cap can be
connected to the VBAT pin. The nominal battery voltage should be 3V. For proper operation, the battery
voltage must always be at least a diode drop (0.7V) below VCC , and is recommended to be below VRST.
The DS87C530 will automatically enter data retention mode when VCC < VBAT. When in data retention
mode, the RTC and SRAM contents are powered from the energy source connected to the VBAT pin and
electrically isolated from the rest of the device. This means that writes to battery backed SFRs and
SRAM are ignored and reads will return erroneous data while in data retention mode. The DS87C530
Data Sheet contains a functional diagram of the internal battery switching circuitry.
The data retention switch voltage, the point at which the device switches into data retention mode, is a
function of the battery voltage, not an absolute reference. Care must be taken when selecting a battery so
that its voltage will stay below VCC during normal operation to prevent an unplanned lockout of the RTC
and SRAM. Although it is unlikely that such a situation would occur, it could become an issue if a
relatively high voltage battery is used. For example, suppose a 4.5V battery is used with a device
operating at a VCC of 5.0V. During normal operation, VCC will be above VBAT , so no problem will
occur. Suppose that a loss of power occurs, and VCC begins to drop. Under normal circumstances, the
device will continue to operate until it reaches VRST (4.0V to 4.25V), at which time device operation will
halt. If VBAT is higher than VRST , however, RTC and SRAM access will be prohibited before the device
enters reset. This means that there may be a short period of time before reset when the device is
operating but could read erroneous data from the RTC or SRAM or fail to write to them. One solution
would be to use the power-fail interrupt to halt reads or writes to the RTC or SRAM when VCC is
dropping. The best approach is to carefully select battery voltages to avoid the problem entirely.
SELECTING A BATTERY
There are a number of battery chemistries and brands that are suitable for use with battery-backed
members of the High-Speed Microcontroller Family. The use of lithium chemistry batteries, such as
Lithium Manganese Dioxide, is preferred as their nominal voltage is approximately 3.0V. Coin cells are
particularly suited for use with the High-Speed Microcontroller Family because of their capacity, low
profile, and small diameter. Many are available with PC mount tabs attached for automated assembly.
Table 15-1 shows a list of some common batteries and their capacities. This list is by no means
exhaustive, and the inclusion or exclusion of any vendor from this list is in no way a comment on the
suitability of a specific battery in a customer’s application.
SUGGESTED BATTERIES FOR USE WITH DS87C530 Table 15-1
MANUFACTURER
Panasonic
Phone:
+1-201 348–5266
MODEL NUMBER
CR1620
CR1616
CR1220
BR1616
BR1225
TYPE
Lithium/Manganese Dioxide
Lithium/Manganese Dioxide
Lithium/Manganese Dioxide
Lithium/poly–carbon monofluoride
Lithium/poly–carbon monofluoride
NOMINAL
VOLTAGE
3V
3V
3V
3V
3V
CAPACITY
70 mAh
50 mAh
35 mAh
48 mAh
38 mAh
Battery life can be calculated by dividing the rated battery capacity by the IBAT current specified on the
device specific data sheet. Note that this determines the minimum battery life; while VCC is applied to the
device, it draws negligible current from the battery, and so battery life will be lengthened accordingly.
Backup current is a function of temperature, and therefore battery life is dependent on the operating
environment.
163 of 175
High-Speed Microcontroller User’s Guide
The registers shown in Table 15-2 are battery-backed, and one or more bits will be indeterminate
following a no-battery reset. They should be initialized as part of a no-battery reset procedure.
BATTERY BACKED SFRS Table 15-2
REGISTER NAME
TRIM
RTASS
RTAS
RTAM
RTAH
RTCC
RTCSS
RTCS
RTCM
RTCH
RTCD0
RTCD1
LOCATION
96h
F2h
F3h
F4h
F5h
F9h
FAh
FBh
FCh
FDh
FEh
FFh
LITHIUM BATTERY CONSIDERATIONS
Lithium primary (non-rechargeable) batteries can fail and/or rupture if subjected to reverse current from
the device they are powering. The battery-switching circuitry inside the DS87C530 was designed to
reduce or eliminate the need for external hardware required to meet battery safety regulations. As shown
in the DS87C530 Data Sheet, a current limiting resistor is always in series with a switching field-effect
transistor, regardless of whether the DS87C530 is drawing current from VCC or VBAT pins. This satisfies
the two mechanism requirement of most safety codes.
164 of 175
High-Speed Microcontroller User’s Guide
SECTION 16: INSTRUCTION SET DETAILS
ARITHMETIC OPERATION
Details of flags modified by each instruction are located in Section 4
INSTRUCTION CODE
MNEMONIC D7 D6 D5 D4 D3 D2 D1 D0
HEX
ADD A, Rn
0
0
1
0
1
n2 n1
n0
28-2F
25
1
0
1
0
0
1
0
ADD A, direct 0
Byte 2
a7 a6 a5 a4 a3 a2 a1 a0
ADD A, @Ri
0
0
1
0
0
1
1
i
26-27
24
0
0
1
0
0
1
0
ADD A, #data
0
d7 d6 d5 d4 d3 d2 d1 d0 Byte 2
ADDC A, Rn
0
0
1
1
1
n2 n1 n0
38-3F
35
1
0
1
0
1
1
0
ADDC A,
0
Byte 2
direct
a7 a6 a5 a4 a3 a2 a1 a0
ADDC A, @Ri 0
0
1
1
0
1
1
i
36-37
34
0
0
1
0
1
1
0
ADDC
0
A,#data
d7 d6 d5 d4 d3 d2 d1 d0 Byte 2
SUBB A, Rn
1
0
0
1
1
n2 n1 n0
98-9F
95
1
0
1
0
1
0
0
SUBB A,
1
Byte 2
direct
a7 a6 a5 a4 a3 a2 a1 a0
SUBB A, @Ri 1
0
0
1
0
1
1
i
96-97
SUBB A,
1
0
0
1
0
1
0
0
94
#data
d7 d6 d5 d4 d3 d2 d1 d0 Byte 2
INC A
0
0
0
0
0
1
0
0
04
INC Rn
0
0
0
0
1
n2 n1 n0
08-0F
INC direct
0
0
0
0
0
1
0
1
05
a7 a6 a5 a4 a3 a2 a1 a0
Byte 2
INC @Ri
0
0
0
0
0
1
1
i
06-07
INC DPTR
1
0
1
0
0
0
1
1
A3
DEC A
0
0
0
1
0
1
0 0
14
DEC Rn
0
0
0
1
1
n2 n1 n0
18-1F
DEC direct
0
0
0
1
0
1
0
1
15
a7 a6 a5 a4 a3 a2 a1 a0
Byte 2
DEC @Ri
0
0
0
1
0
1
1
i
16-17
MUL AB
1
0
1
0
0
1
0
0
A4
DIV AB
1
0
0
0
0
1
0
0
84
165 of 175
BYTE
1
2
CYCLE
1
2
EXPLANATION
(A) = (A) + (Rn)
(A) = (A) + (direct)
1
2
1
2
(A) = (A) + ((Ri))
(A) = (A) + #data
1
2
1
2
(A) = (A)+(C)+(Rn)
(A) = (A)+(C)+(direct)
1
2
1
2
(A) = (A)+(C)+((Ri))
(A) = (A)+(C)+#data
1
2
1
2
(A) = (A)-(C)-(Rn)
(A) = (A)-(C)-(direct)
1
2
1
2
(A) = (A)-(C)-((Ri))
(A) = (A)-(C)-#data
1
1
2
1
1
2
(A) = (A) + 1
(Rn) = (Rn) + 1
(direct) = (direct)+1
1
1
1
1
2
1
3
1
1
2
((Ri)) = ((Ri)) + 1
(DPTR)=(DPTR)+1
(A) = (A) - 1
(Rn) = (Rn) - 1
(direct) = (direct)-1
1
1
1
5
1
5
((Ri)) = ((Ri)) - 1
(B15–8 ), (A7–0)
= (A) X (B)
(A15–8 ), (A7–0 )
= (A) ÷ (B)
ARITHMETIC OPER.
High-Speed Microcontroller User’s Guide
D7
1
D6
1
ANL A, Rn
ANL A, direct
0
0
a7
0
0
d7
0
a7
0
a7
d7
0
0
a7
0
0
d7
0
1
1
a6
1
1
d6
1
a6
1
a6
d6
1
1
a6
1
1
d6
1
0
0
a5
0
0
d5
0
a5
0
a5
d5
0
0
a5
0
0
d5
0
1
1
a4
1
1
d4
1
a4
1
a4
d4
0
0
a4
0
0
d4
0
1
0
a3
0
0
d3
0
a3
0
a3
d3
1
0
a3
0
0
d3
0
n2
1
a2
1
1
d2
0
a2
0
a2
d2
n2
1
a2
1
1
d2
0
XRL A, @ Ri
XRL A, #data
0
a7
d7
0
0
a7
0
0
1
a6
d6
1
1
a6
1
1
0
a5
d5
1
1
a5
1
1
0
a4
d4
0
0
a4
0
0
0
a3
d3
1
0
a3
0
0
XRL direct, A
0
1
1
0
XRL direct,
#data
0
a7
d7
1
1
1
a6
d6
1
1
1
a5
d5
1
1
0
a4
d4
0
1
ANL A, @Ri
ANL A, #data
ANL direct, A
ANL direct,
#data
ORL A, Rn
ORL A, direct
LOGICAL OPERATION
INSTRUCTION CODE
D5 D4 D3 D2 D1
0
1
0
1
0
MNEMONIC
DA A
ORL A, @Ri
ORL A, #data
ORL direct, A
ORL direct,
#data
XRL A, Rn
XRL A, direct
CLR A
CPL A
D0
0
HEX
D4
BYTE
1
CYCLE
1
n1
0
a1
1
0
d1
1
a1
1
a1
d1
n1
1
a1
1
0
d1
1
n0
i
a0
i
0
d0
0
a0
1
a0
d0
n0
I
a0
i
0
d0
0
1
2
1
2
(A) = (A) AND (Rn)
(A) = (A) AND (direct)
1
2
1
2
(A) = (A) AND ((Ri))
(A)=(A) AND #data
2
2
3
3
(direct) =
(direct) AND A
(direct) =
(direct) AND #data
1
2
1
2
1
2
1
2
2
2
0
a2
d2
n2
1
a2
1
1
1
a1
d1
n1
0
a1
1
0
1
a0
d0
n0
1
a0
i
0
3
3
1
2
1
2
1
2
1
2
0
0
1
0
2
2
0
a3
d3
0
0
0
a2
d2
1
1
1
a1
d1
0
0
1
a0
d0
0
0
58-5F
55
Byte 2
56-57
54
Byte 2
52
Byte 2
53
Byte 2
Byte 3
48-4F
45
Byte 2
46-47
44
Byte 2
42
Byte 2
43
Byte 2
Byte 3
68-6F
65
Byte 2
66-67
64
Byte 2
62
Byte 2
63
Byte 2
Byte 3
E4
F4
3
3
1
1
1
1
166 of 175
EXPLANATION
Contents of Accumulator
are BCD,
IF [[(A3-0 ) > 9] OR
[(AC) = 1]] THEN
(A3-0 ) = (A3-0 ) + 6
AND
IF [[(A7-4 ) > 9] OR
[(C) = 1]] THEN
(A7-4 ) = (A7-4 ) + 6
(A) = (A) OR (Rn)
(A) =
(A) OR (direct)
(A) = (A) OR ((Ri))
(A) = (A) OR #data
(direct) =
(direct) OR (A)
(direct) =
(direct) OR #data
(A) = (A) XOR (Rn)
(A) =
(A) XOR (direct)
(A) = (A) XOR ((Ri))
(direct) =
(A) XOR #data
(direct) =
(direct) XOR (A)
(direct) =
(direct) XOR #data
(A) = 0
(A) = ( A )
High-Speed Microcontroller User’s Guide
MNEMONIC
RL A
D7
0
D6
0
INSTRUCTION CODE
D5 D4 D3 D2 D1
1
0
0
0
1
D0
1
HEX
23
BYTE
1
CYCLE
1
EXPLANATION
A7 A6 A5 A4 A3 A2 A1 A0
The contents of the
accumulator are
rotated left by one bit.
RLC A
0
0
1
1
0
0
1
1
33
1
1
LOGICAL OPERATION
C
RR A
0
0
0
0
0
0
1
1
03
1
1
A7 A6 A5 A4 A3 A2 A0 A1
The contents of the
accumulator are rotated
right by one bit.
RRC A
0
0
0
1
0
0
1
1
13
1
1
C
DATA TRANSFER
A7 A6 A5 A4 A3 A2 A0 A1
The contents of the
accumulator are rotated
right by one bit.
SWAP A
MOV A, Rn
MOV A,
direct
MOV A, @Ri
MOV A,
#data
MOV Rn, A
MOV Rn,
direct
MOV Rn,
#data
MOV direct,
A
MOV direct,
Rn
MOVdirect1,
direct2
MOV direct,
@Ri
1
1
1
a7
1
0
d7
1
1
a7
0
d7
1
a7
1
a7
1
a7
a7
1
a7
1
1
1
a6
1
1
d6
1
0
a6
1
d6
1
a6
0
a6
0
a6
a6
0
a6
0
1
1
a5
1
1
d5
1
1
a5
1
d5
1
a5
0
a5
0
a5
a5
0
a5
0
0
0
a5
0
1
d4
1
0
a5
1
d4
1
a4
0
a4
0
a4
a4
0
a4
0
1
0
a3
0
0
d3
1
1
a3
1
d3
0
a3
1
a3
0
a3
a3
0
a3
1
n2
1
a2
1
1
d2
n2
n2
a2
n2
d2
1
a2
n2
a2
1
a2
a2
1
a2
0
n1
0
a1
1
0
d1
n1
n1
a1
n1
d1
0
a1
n1
a1
0
a1
a1
1
a1
0
n0
1
a0
i
0
d0
n0
n0
a0
n0
d0
1
a0
n0
a0
1
a0
a0
i
a0
C4
E8-EF
E5
Byte 2
E6-E7
74
Byte 2
F8-FF
A8-AF
Byte 2
78-7F
Byte 2
F5
Byte 2
88-8F
Byte 2
85
Byte 2
Byte 3
86-87
Byte 2
167 of 175
A7 A6 A5 A4 A3 A2 A0 A1
1
1
2
1
1
2
The contents of the
accumulator are rotated
right by one bit.
(A3-0 ) ? (A7-4 )
(A) = (Rn)
(A) = (direct)
1
2
1
2
(A) = ((Ri))
(A) = #data
1
2
1
2
(Rn) = (A)
(Rn) = (direct)
2
2
(Rn) = #data
2
2
(direct) = (A)
2
2
(direct) = (Rn)
3
3
2
2
(direct1) = (direct2)
(source)
(destination)
(direct) = ((Ri))
High-Speed Microcontroller User’s Guide
MNEMONIC
MOV direct,
#data
DATA TRANSFER
MOV @Ri, A
MOV @Ri,
direct
MOV @Ri,
#data
MOV DPTR,
#data16
MOVC A,
@A + DPTR
MOVC A,
@A + PC
MOVX A,
@Ri
MOVX
@DPTR,
MOVX @Ri,
A
MOVX
@DPTR,A
PUSH direct
POP direct
XCH A, Rn
XCH A,
direct
XCH A, @Ri
XCHD A,
@Ri
INSTRUCTION CODE
D5 D4 D3 D2 D1
0
1
0
1
1
a5 a4 a3 a2 a1
d5 d4 d3 d2 d1
1
1
0
1
1
1
1
0
0
1
a5 a4 a3 a2 a1
1
1
0
1
1
d5 d4 d3 d2 d1
0
0
0
1
0
d5 d4 d3 d2 d1
d5 d4 d3 d2 d1
0
1
0
0
1
D0
1
a0
d0
i
i
a0
i
d0
0
d0
d0
1
HEX
75
Byte 2
Byte 3
F6-F7
A6-A7
Byte 2
76-77
Byte 2
90
Byte 2
Byte 3
93
BYTE
3
CYCLE
3
1
2
1
2
((Ri)) = A
((Ri)) = (direct)
2
2
((Ri)) = #data
3
3
1
3
(DPTR) = #data15-0
(DPH) = #data15-8
(DPL) = #data7-0
(A)=((A) + (DPTR))
1
1
83
1
3
(A) = ((A) + (PC))
0
1
i
E2-E3
1
2-9
(A) = ((Ri))
0
0
0
0
E0
1
2-9
(A) = ((DPTR))
1
0
0
1
i
F2-F3
1
2-9
((Ri)) = (A)
1
1
0
0
0
0
F0
1
2-9
((DPTR)) = (A)
0
a5
0
a5
0
0
a5
0
0
0
a4
1
a4
0
0
a4
0
1
0
a3
0
a3
1
0
a3
0
0
0
a2
0
a2
n2
1
a2
1
1
0
a1
0
a1
n1
0
a1
1
1
0
a0
0
a0
n0
1
a0
i
i
C0
Byte 2
D0
Byte 2
C8-CF
C5
Byte 2
C6-C7
D6-D7
2
2
2
2
1
2
1
2
(SP) = (SP) + 1
((SP)) = (direct)
(direct) = ((SP))
(SP) = (SP) - 1
(A) = (Rn)
(A) = (direct)
1
1
1
1
(A) = ((Ri))
(A3-0) = ((Ri3-0 ))
D7
0
a7
d7
1
1
a7
0
d7
1
d7
d7
1
D6
1
a6
d6
1
0
a6
1
d6
0
d6
d6
0
1
0
0
0
0
0
1
1
1
0
0
1
1
1
0
1
1
1
1
1
1
a7
1
a7
1
1
a7
1
1
1
a6
1
a6
1
1
a6
1
1
168 of 175
EXPLANATION
(direct) = #data
High-Speed Microcontroller User’s Guide
BOOLEAN VARIABLE MANIPULATION
MNEMONIC
CLR C
CLR bit
SETB C
SETB bit
CPL C
CPL bit
ANL C, bit
ANL C,
bit
ORL C, bit
ORL C,
bit
MOV C, bit
MOV bit, C
D7
1
1
b7
1
1
b7
1
D6
1
1
b6
1
1
b6
0
1
b7
1
b7
1
b7
1
b7
1
b7
1
b7
1
b7
0
b6
0
b6
0
b6
1
b6
0
b6
0
b6
0
b6
INSTRUCTION CODE
D5 D4 D3 D2 D1
0
0
0
0
1
1
0
0
0
0
b5 b4 b3 b2 b1
0
1
0
0
1
1
0
0
1
0
b5 b4 b3 b2 b1
1
1
0
0
1
D0
1
0
b0
1
0
b0
1
HEX
C3
C2
Byte 2
D3
D2
Byte 2
B3
BYTE
1
2
CYCLE
1
2
1
2
1
2
(C) = 1
(bit) = 1
1
1
(C) = ( C )
1
b1
1
b1
0
b1
1
b1
0
b1
1
b1
1
b1
0
b0
0
b0
0
b0
0
b0
0
b0
0
b0
0
b0
B2
Byte 2
82
Byte 2
B0
Byte 2
72
Byte 2
A0
Byte 2
A2
Byte 2
92
Byte 2
2
2
(bit) = ( bit )
2
2
(C) = (C) AND (bit)
2
2
(C) = (C) AND ( bit )
2
2
(C) = (C) OR (bit)
2
2
(C) = (C) OR ( bit )
2
2
(C) = (bit)
2
2
(bit) = (C)
1
b5
0
b5
1
b5
1
b5
1
b5
1
b5
0
b5
1
b4
0
b4
1
b4
1
b4
0
b4
0
b4
1
b4
0
b3
0
b3
0
b3
0
b3
0
b3
0
b3
0
b3
0
b2
0
b2
0
b2
0
b2
0
b2
0
b2
0
b2
169 of 175
EXPLANATION
(C) = 0
(bit) = 0
High-Speed Microcontroller User’s Guide
MNEMONIC
D0
1
a0
HEX
Byte 1
Byte 2
BYTE
2
CYCLE
3
0
a10
a2
1
a9
a1
0
a8
a0
12
Byte 2
Byte 3
3
4
0
0
1
0
22
1
4
1
0
0
1
0
32
1
4
a8
a5
0
a13
a5
0
r5
1
0
a4
0
a12
a4
0
r4
1
0
a3
0
a11
a3
0
r3
0
0
a2
0
a10
a2
0
r2
0
0
a1
1
a9
a1
0
r1
1
1
a0
0
a8
a0
0
r0
1
Byte 1
Byte 2
02
Byte 2
Byte 3
80
Byte 2
73
2
3
3
4
2
3
1
3
0
r6
0
r5
0
r4
0
r3
0
r2
0
r1
0
r0
60
Byte 2
2
3
0
r6
0
r5
0
r4
0
r3
0
r2
0
r1
0
r0
70
Byte 2
2
3
D6
a9
a6
0
a15
a7
0
a14
a6
0
a13
a5
1
a12
a5
0
a11
a3
RET
0
0
1
0
RETI
0
0
1
a10
a7
0
a15
a7
1
r7
0
a9
a6
0
a14
a6
0
r6
1
1
r7
1
r7
ACALL addr
11
LCALL addr
16
PROGRAM BRANCHING
INSTRUCTION CODE
D5 D4 D3 D2 D1
0
0
0
1
a8
a5 a8 a3 a2 a1
D7
a10
a7
AJMP addr
11
LJMP addr
16
SJMP rel
JMP @A +
DPTR
JZ rel
JNZ rel
170 of 175
EXPLANATION
(PC) = (PC) + 2
(SP) = (SP) + 1
((SP)) = (PC7-0 )
(SP) = (SP) + 1
((SP)) = (PC15-8 )
(PC)=page address
(PC) = (PC) + 3
(SP) = (SP) + 1
((SP)) = (PC7-0 )
(SP) = (SP) + 1
((SP)) = (PC15-8 )
(PC) = addr15-0
(PC15-8 ) = ((SP))
(SP) = (SP) - 1
(PC7-0 ) = ((SP))
(SP) = (SP) - 1
(PC15-8 ) = ((SP))
(SP) = (SP) - 1
(PC7-0 ) = ((SP))
(SP) = (SP) - 1
(PC) = (PC) + 2
(PC10-0 ) = page addr
(PC) = addr15-0
(PC) = (PC) + 2
(PC) = (PC) + rel
(PC) = (A) + (DPTR)
(PC) = (PC) + 2
IF (A) = 0 THEN
(PC) = (PC) + rel
(PC) = (PC) + 2
IF (A) ? 0 THEN
(PC) = (PC) + rel
High-Speed Microcontroller User’s Guide
D7
0
r7
INSTRUCTION CODE
D6 D5 D4 D3 D2 D1
0
0
0
0
0
1
r1
r2
r3
r4
r5
r6
D0
0
r0
HEX
40
Byte 2
BYTE
2
CYCLE
3
0
r7
1
r6
0
r5
1
r4
0
r3
0
r2
0
r1
0
r0
50
Byte 2
2
3
0
b7
r7
0
b7
r7
0
b7
r7
0
b6
r6
0
b6
r6
0
b6
r6
1
b5
r5
0
b5
r5
0
b5
r5
0
b4
r4
1
b4
r4
1
b4
r4
0
b3
r3
0
b3
r3
0
b3
r3
0
b2
r2
0
b2
r2
0
b2
r2
0
b1
r1
0
b1
r1
0
b1
r1
0
b0
r0
0
b0
r0
0
b0
r0
20
Byte 2
Byte 3
30
Byte 2
Byte 3
10
Byte 2
Byte 3
3
4
3
4
3
4
CJNE A,
direct, rel
0
a7
r7
0
a6
r6
0
a5
r5
1
a4
r4
0
a3
r3
0
a2
r2
0
a1
r1
0
a0
r0
B5
Byte 2
Byte 3
3
4
CJNE A,
#data, rel
1
d7
r7
0
d6
r6
1
d5
r5
1
d4
r4
0
d3
r3
1
d2
r2
0
d1
r1
0
d0
r0
B4
Byte 2
Byte 3
3
4
CJNE Rn,
#data, rel
1
d7
r7
0
d6
r6
1
d5
r5
1
d4
r4
1
d3
r3
n2
d2
r2
n1
d1
r1
n0
d0
r0
B8-BF
Byte 2
Byte 3
3
4
CJNE @Ri,
#data, rel
1
d7
r7
0
d6
r6
1
d5
r5
1
d4
r4
0
d3
r3
1
d2
r2
1
d1
r1
i
d0
r0
B6-B7
Byte 2
Byte 3
3
4
MNEMONIC
JC rel
JNC rel
JB bit, rel
JNB bit, rel
PROGRAM BRANCHING
JBC bit,
direct, rel
171 of 175
EXPLANATION
(PC) = (PC) + 2
IF (C) = 1 THEN
(PC) = (PC) + rel
(PC) = (PC) + 2
IF (C) ? 0 THEN
(PC) = (PC) + rel
(PC) = (PC) + 3
IF (bit) = 1 THEN
(PC) = (PC) + rel
(PC) = (PC) + 3
IF (bit) = 0 THEN
(PC) = (PC) + rel
(PC) = (PC) + 3
IF (bit) = 1 THEN
(bit) = 0 (PC) =
(PC) + rel
(PC) = (PC) + 3
IF (direct) < (A)
THEN (PC) = (PC)
+ rel and (C) = 0
OR
IF (direct) > (A)
THEN (PC) = (PC)
+ rel and (C) = 1
(PC) = (PC) + 3
IF #data < (A)
THEN (PC) = (PC)
+ rel and (C) = 0
OR
IF #data > (A)
THEN (PC) = (PC)
+ rel and (C) = 1
(PC) = (PC) + 3
IF #data < (Rn)
THEN (PC) = (PC)
+ rel and (C) = 0
OR
IF #data > (Rn)
THEN (PC) = (PC)
+ rel and (C) = 1
(PC) = (PC) + 3
IF #data < ((Ri))
THEN (PC) = (PC)
+ rel and (C) = 0
OR
IF #data > ((Ri))
THEN (PC) = (PC)
+ rel and (C) = 1
High-Speed Microcontroller User’s Guide
MNEMONIC
DJNZ Rn, rel
DJNZ direct,rel
NOP
D7
1
r7
INSTRUCTION CODE
D6 D5 D4 D3 D2 D1
n2 n1
1
1
0
1
r1
r2
r3
r4
r5
r6
D0
n0
r0
HEX
D8-Df
Byte 2
BYTE
2
CYCLE
3
1
a7
r7
1
a6
r6
0
a5
r5
1
a4
r4
0
a3
r3
1
a2
r2
0
a1
r1
1
a0
r0
D5
Byte 2
Byte 3
3
4
0
0
0
0
0
0
0
0
00
1
172 of 175
1
EXPLANATION
(PC) = (PC) + 2
(Rn) = (Rn) - 1
IF (Rn) ≠ 0 THEN
(PC) = (PC) + rel
(PC) = (PC) + 3
(direct) = (direct) - 1
IF (direct) ? 0 THEN
(PC) = (PC) + rel
(PC) = (PC) + 1
High-Speed Microcontroller User’s Guide
SECTION 17: TROUBLESHOOTING
DEVICE OPERATES AT 1/3 OF CRYSTAL SPEED
The High-Speed Microcontroller Family operates from the primary or fundamental mode of the external
crystal. Many off-the-shelf high-frequency crystals are specified to operate from their third overtone.
When used with a High-Speed Microcontroller, these crystals will resonate in their primary mode, which
will appear to be 1/3 of the rated crystal speed. Make sure that any crystals used will operate at their
rated speed in primary mode.
DEVICE RESETS FOR NO REASON
During the debugging process, it may be necessary to isolate the cause of an unexpected device reset.
Because resets are initiated by a limited number of sources, it is relatively easy to determine their source
by interrogating a few bits. These bits should be interrogated early in the code following a reset to
determine its source. As a debug tool, software could set the state of one or more port pins to indicate the
type of reset to the designer. Note that power supply problems or glitches will appear as unplanned
power-on resets.
SOURCE
Power–on reset
Watchdog reset
External reset
POR BIT
WDCON.6
1
0
0
WTRF BIT
WDCON.3
0
1
0
ACCESS TO INTERNAL MOVX SRAM IS UNSUCCESSFUL
The internal MOVX SRAM available on some members of the High-Speed Microcontroller Family is
disabled after any reset. To enable the on-chip SRAM, the software should configure the Data Memory
Enable bits (PMR.1-0) as needed.
When VCC drops below VBAT , access to the SRAM is disabled to prevent corruption of the data. If the
battery voltage is greater than VRST, this means that the processor may continue to operate while SRAM
access is denied. Make sure that the battery voltage remains below the minimum VRST.
REAL-TIME CLOCK DOES NOT OPERATE OR KEEP ACCURATE TIME.
The state of the real-time clock (RTC) used on the DS87C530 is undefined following a no-battery reset or
battery attach. The RTC oscillator must be enabled by setting the RTCE bit (RTCC.0) for the RTC to
work.
The RTC is guaranteed to a minimum accuracy of ± 2 minutes per month over the rated temperature and
voltage specifications. If the time is found to be less accurate than this, it is most likely due to the
selection of crystal. Make sure that the RTC crystal is 32.768 kHz, and either 12.5 pF or 6 pF
capacitance. The 12/6 bit (TRIM.6) setting should correspond to the crystal in use. Unlike other crystals,
external load capacitors should not be used with the RTC. These will seriously distort the accuracy of the
clock. Additional information on design considerations with the RTC can be found in Applications Note
79, Using the DS87C530 Real Time Clock.
173 of 175
High-Speed Microcontroller User’s Guide
SERIAL PORT DOES NOT WORK
The serial port is not a complicated peripheral, but there are many elements that need to be initialized.
The following checklist is provided to help in debugging.
1. Have the appropriate port latch bits (P3.0, P3.1, P1.2, or P1.3) been set to 1 to enable the serial port
functions?
2. Has the correct timebase been selected? (4 clocks per tick or 12 clocks per tick)
3. Is the appropriate timer reload value loaded?
4. Is the appropriate timer mode selected?
5. Is the appropriate timer running by setting TR0, TR1, or TR2 bits?
6. Is the correct serial port mode selected?
7. If desired, is the serial port doubler bit, SMOD, set? (PCON.7 or WDCON.7)
8. If desired, is the receive enable bit (REN_0 or REN_1) set?
9. Is the serial port interrupt enabled?
10. Is the global interrupt enable bit set?
HIGH-SPEED MICROCONTROLLER DOES NOT WORK IN EXISTING 8051
DESIGN
Although the High-Speed Microcontroller Family was designed as a drop in replacement for the 8051
family, occasionally a developer may notice problems when inserting into an existing design. Often these
problems are related to slow memory interfaces which cannot keep up with the increased throughput of
the faster microcontroller. In addition, software timing loops will run faster, possibly changing program
operation. These and other effects are described in Application Note 56 (The DS80C320 as a Drop-In
Replacement for the 8032). Application Note 57 (DS80C320 Memory Interface Timing) discusses
memory interface timing for the DS80C320. Application Note 89 (High-Speed Micro Memory Interface
Timing) discusses interfacing other members of the High-Speed Microcontroller family to external
memory.
174 of 175
High-Speed Microcontroller User’s Guide
SECTION 18: MICROCONTROLLER DEVELOPMENT SUPPORT
TECHNICAL SUPPORT
Dallas Semiconductor has a wide range of services designed to support its customers. Microcontroller
applications engineers are available Monday through Friday (excluding holidays) to provide technical
support from 8 am to 5 pm Central Standard Time. They can be reached by telephone and electronic mail
at the numbers shown.
Application Support: +1-972-371-4167
+1-972-371-3600 (fax)
Email:
[email protected]
Dallas Semiconductor maintains a presence on the Internet, with both a World Wide Web home page and
an anonymous FTP site. Data sheets are subject to revision, and these services contain the most current
data sheet information available. The home page has access to company information, data sheets,
application notes, and product information. The ftp server hosts data sheets, application notes, and
software examples.
World Wide Web Home page:
http://www.dalsemi.com
Microcontroller products home page:http://www.dalsemi.com/Prod_info/Micros/
Anonymous ftp:
ftp.dalsemi.com
DEVELOPMENT TOOLS
Because the High-Speed Microcontroller family was designed for maximum compatibility with existing
8051 microcontrollers, users will find that most of their existing 8051 tools will work with our products.
To aid our customers, Dallas Semiconductor maintains a list of development tool vendors on its website
at http://www.dalsemi.com/microtools.html. This page is very useful when attempting to locate
commonly used microcontroller aids such as compilers, test clips, sockets, programmers, programming
adapters, reference books, emulators, crystals and development boards.
SOFTWARE COMPATIBILITY
Dallas Semiconductor microcontrollers execute the 8051 instruction set and are object code compatible
with other 8051-based products. The special features of Dallas Semiconductor microcontrollers are
accessed via Special Function Registers unique to our products, but the devices do not use any new
instructions. The new Special Function Registers can be easily defined in the user's software with
EQUATE statements or in a setup file. Once defined, these new Special Function Registers receive the
same treatment as any of the original 8051 registers. This means that Dallas Semiconductor
microcontrollers are compatible with almost every 8051-based software tool available.
HIGH-LEVEL LANGUAGE COMPILERS
Like assemblers, compilers must be informed of the existence and location of the Special Function
Registers unique to Dallas Semiconductor microcontrollers. When using C, it is commonly necessary to
identify the starting address for various read/write segments such as XDATA and Stack.
In addition, it is recommended that the large memory model be used in conjunction with C Compilers.
This places the stack in off-chip SRAM. Microcontroller systems usually have an abundance of such
SRAM compared to ROM-based systems. While off-chip stack results in slower execution time, the stack
size becomes virtually unlimited.
175 of 175