ATMEL AT89C55WD User Manual

Features

• Compatible with MCS

• 20K Bytes of Reprogrammable Flash Memory

• Endurance: 1000 Write/Erase Cycles

• 4V to 5.5V Operating Range

• Fully Static Operation: 0 Hz to 33 MHz

• Three-level Program Memory Lock

• 256 x 8-bit Internal RAM

• 32 Programmable I/O Lines

• Three 16-bit Timer/Counters

• Eight Interrupt Sources

• Programmable Serial Channel

• Low-power Idle and Power-down Modes

• Interrupt Recovery from Power-down Mode

• Hardware Watchdog Timer

• Dual Data Pointer

• Power-off Flag

• Green (Pb/Halide-free) Packaging Option

-51 Products

1. Description

The AT89C55WD is a low-power, high-performance CMOS 8-bit microcontroller with 20K bytes of Flash programmable read only memory and 256 bytes of RAM. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry standard 80C51 and 80C52 instruction set and pinout. The on-chip Flash allows the program memory to be user programmed by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C55WD is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications.

8-bit Microcontroller with 20K Bytes Flash

AT89C55WD

The AT89C55WD provides the following standard features: 20K bytes of Flash, 256 bytes of RAM, 32 I/O lines, three 16-bit timer/counters, a six-vector, two-level interrupt architecture, a full-duplex serial port, on-chip oscillator, and clock circuitry. In addition, the AT89C55WD is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-down Mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next external interrupt or hardware reset.

1921C–MICRO–3/05

2. Pin Configurations

2.1 44A – 44-lead TQFP

2.2 44J – 44-lead PLCC

(RXD) P3.0

(TXD) P3.1 (INT0) P3.2 (INT1) P3.3

(T0) P3.4 (T1) P3.5

P1.5 P1.6 P1.7 RST

(RXD) P3.0

NC (TXD) P3.1 (INT0) P3.2 (INT1) P3.3

(T0) P3.4 (T1) P3.5

P1.4

P1.3

P1.2

P1.1 (T2 EX)

4443424140393837363534

P1.5

P1.6

P1.7

RST

5 6

7 8 9 10 11

1213141516171819202122

XTAL2

XTAL1

(RD) P3.7

(WR) P3.6

P1.4

P1.3

P1.2

P1.1 (T2 EX)

65432

7 8 9 10 11 12 13 14 15 16 17

1819202122232425262728

XTAL2

XTAL1

(RD) P3.7

(WR) P3.6

P1.0 (T2)NCVCC

GND

(A8) P2.0

P1.0 (T2)NCVCC

4443424140

GND

(A8) P2.0

P0.0 (AD0)

P0.1 (AD1)

P0.2 (AD2)

(A9) P2.1

(A10) P2.2

(A11) P2.3

P0.0 (AD0)

P0.1 (AD1)

(A9) P2.1

(A10) P2.2

P0.3 (AD3)

33 32 31 30 29 28 27 26 25 24 23

(A12) P2.4

P0.2 (AD2)

P0.3 (AD3)

39 38 37 36 35 34 33 32 31 30 29

(A11) P2.3

(A12) P2.4

P0.4 (AD4) P0.5 (AD5) P0.6 (AD6) P0.7 (AD7) EA/VPP NC ALE/PROG PSEN P2.7 (A15) P2.6 (A14) P2.5 (A13)

2.3 40P6 – 40-lead PDIP

AT89C55WD

(T2) P1.0

(T2EX) P1.1

P1.2 P1.3 P1.4 P1.5 P1.6 P1.7

RST (RXD) P3.0 (TXD) P3.1 (INT0) P3.2 (INT1) P3.3

(T0) P3.4 (T1) P3.5

(WR) P3.6

(RD) P3.7

XTAL2 XTAL1

GND

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21

VCC P0.0 (AD0) P0.1 (AD1) P0.2 (AD2) P0.3 (AD3) P0.4 (AD4) P0.5 (AD5) P0.6 (AD6) P0.7 (AD7) EA/VPP ALE/PROG PSEN P2.7 (A15) P2.6 (A14) P2.5 (A13) P2.4 (A12) P2.3 (A11) P2.2 (A10) P2.1 (A9) P2.0 (A8)

1921C–MICRO–3/05

3. Block Diagram

AT89C55WD

GND

RAM ADDR.

ACC

TMP2

P0.0 - P0.7

PORT 0 DRIVERS

RAM

ALU

PORT 0

LATCH

TMP1

PORT 2 DRIVERS

PORT 2

LATCH

POINTER

P2.0 - P2.7

QUICK FLASH

STACK

PROGRAM

ADDRESS

BUFFER

INCREMENTER

PSEN

ALE/PROG

EA / V

RST

INTERRUPT, SERIAL PORT,

AND TIMER BLOCKS

PROGRAM

PSW

TIMING

AND

CONTROL

OSC

INSTRUCTION

WATCH

DOG

PORT 1

LATCH

PORT 1 DRIVERS

P1.0 - P1.7

PORT 3

LATCH

PORT 3 DRIVERS

P3.0 - P3.7

COUNTER

DUAL DPTR

1921C–MICRO–3/05

4. Pin Description

4.1 VCC

Supply voltage.

4.2 GND

Ground.

4.3 Port 0

Port 0 is an 8-bit open drain bi-directional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high-impedance inputs.

Port 0 can also be configured to be the multiplexed low-order address/data bus during accesses to external program and data memory. In this mode, P0 has internal pull-ups.

Port 0 also receives the code bytes during Flash programming and outputs the code bytes during program verification. External pull-ups are required during program verification.

4.4 Port 1

Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (I

In addition, P1.0 and P1.1 can be configured to be the timer/counter 2 external count input (P1.0/T2) and the timer/counter 2 trigger input (P1.1/T2EX), respectively, as shown in the following table.

) because of the internal pull-ups.

4.5 Port 2

Port 1 also receives the low-order address bytes during Flash programming and verification.

Port Pin Alternate Functions

P1.0 T2 (external count input to Timer/Counter 2), clock-out

P1.1 T2EX (Timer/Counter 2 capture/reload trigger and direction control)

Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2 output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (I

Port 2 emits the high-order address byte during fetches from external program memory and during accesses to external data memory that use 16-bit addresses (MOVX @ DPTR). In this application, Port 2 uses strong internal pull-ups when emitting 1s. During accesses to external data memory that use 8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special Function Register.

Port 2 also receives the high-order address bits and some control signals during Flash programming and verification.

) because of the internal pull-ups.

AT89C55WD

1921C–MICRO–3/05

4.6 Port 3

AT89C55WD

Port 3 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (I

Port 3 receives some control signals for Flash programming and verification.

Port 3 also serves the functions of various special features of the AT89C55WD, as shown in the following table.

Port Pin Alternate Functions

P3.0 RXD (serial input port)

P3.1 TXD (serial output port)

P3.2 INT0

) because of the pull-ups.

(external interrupt 0)

4.7 RST

4.8 ALE/PROG

P3.3 INT1

P3.4 T0 (timer 0 external input)

P3.5 T1 (timer 1 external input)

P3.6 WR

P3.7 RD

(external interrupt 1)

(external data memory write strobe)

(external data memory read strobe)

Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device. This pin drives High for 98 oscillator periods after the Watchdog times out. The DISRTO bit in SFR AUXR (address 8EH) can be used to disable this feature. In the default state of bit DISRTO, the RESET HIGH out feature is enabled.

Address Latch Enable is an output pulse for latching the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG

) during Flash

programming.

In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator frequency and may be used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external data memory.

If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in external execution mode.

4.9 PSEN

1921C–MICRO–3/05

Program Store Enable is the read strobe to external program memory.

When the AT89C55WD is executing code from external program memory, PSEN twice each machine cycle, except that two PSEN

activations are skipped during each access to

external data memory.

is activated

4.10 EA/VPP

External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA

should be strapped to VCC for internal program executions.

will be internally latched on reset.

This pin also receives the 12V programming enable voltage (V

) during Flash programming.

4.11 XTAL1

Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

4.12 XTAL2

Output from the inverting oscillator amplifier.

5. Special Function Registers

A map of the on-chip memory area called the Special Function Register (SFR) space is shown in Table 5-1.

Table 5-1. AT89C55WD SFR Map and Reset Values

0F8H 0FFH

0F0H

0E8H 0EFH

0E0H

0D8H 0DFH

0D0H

0C8H

00000000

ACC

00000000

PSW

00000000

T2CON

00000000

T2MOD

XXXXXX00

RCAP2L

00000000

RCAP2H

00000000

TL2

00000000

TH2

00000000

0F7H

0E7H

0D7H

0CFH

0C0H 0C7H

0B8H

0B0H

0A8H

0A0H

98H

90H

88H

80H

XX000000

11111111

0X000000

11111111

SCON

00000000

11111111

TCON

00000000

11111111

SBUF

XXXXXXXX

TMOD

00000000

00000111

AT89C55WD

AUXR1

XXXXXXX0

TL0

00000000

DP0L

00000000

TL1

00000000

DP0H

00000000

TH0

00000000

DP1L

00000000

TH1

00000000

DP1H

00000000

WDTRST

XXXXXXXX

AUXR

XXX00XX0

PCON

0XXX0000

1921C–MICRO–3/05

0BFH

0B7H

0AFH

0A7H

9FH

97H

8FH

87H

AT89C55WD

Note that not all of the addresses are occupied, and unoccupied addresses may not be implemented on the chip. Read accesses to these addresses will in general return random data, and write accesses will have an indeterminate effect.

User software should not write 1s to these unlisted locations, since they may be used in future products to invoke new features. In that case, the reset or inactive values of the new bits will always be 0.

Timer 2 Registers: Control and status bits are contained in registers T2CON (shown in Table 5-

2) and T2MOD (shown in Table 5-2) for Timer 2. The register pair (RCAP2H, RCAP2L) are the

Capture/Reload registers for Timer 2 in 16-bit capture mode or 16-bit auto-reload mode.

Interrupt Registers: The individual interrupt enable bits are in the IE register. Two priorities can be set for each of the six interrupt sources in the IP register.

Dual Data Pointer Registers: To facilitate accessing both internal and external data memory, two banks of 16-bit Data Pointer Registers are provided: DP0 at SFR address locations 82H83H and DP1 at 84H-85H. Bit DPS = 0 in SFR AUXR1 selects DP0 and DPS = 1 selects DP1. The user should always initialize the DPS bit to the appropriate value before accessing the respective Data Pointer Register.

Power Off Flag: The Power Off Flag (POF) is located at bit 4 (PCON.4) in the PCON SFR. POF is set to “1” during power up. It can be set and reset under software control and is not affected by reset.

Table 5-2. T2CON—Timer/Counter 2 Control Register

T2CON Address = 0C8H Reset Value = 0000 0000B

Bit Addressable

Bit

Symbol Function

TF2

EXF2

RCLK

TCLK

EXEN2

TR2 Start/Stop control for Timer 2. TR2 = 1 starts the timer.

C/T2

CP/RL2

TF2 EXF2 RCLK TCLK EXEN2 TR2 C/T2

76543210

Timer 2 overflow flag set by a Timer 2 overflow and must be cleared by software. TF2 will not be set when either RCLK = 1 or TCLK = 1.

Timer 2 external flag set when either a capture or reload is caused by a negative transition on T2EX and EXEN2 = 1. When Timer 2 interrupt is enabled, EXF2 = 1 will cause the CPU to vector to the Timer 2 interrupt routine. EXF2 must be cleared by software. EXF2 does not cause an interrupt in up/down counter mode (DCEN = 1).

Receive clock enable. When set, causes the serial port to use Timer 2 overflow pulses for its receive clock in serial port Modes 1 and 3. RCLK = 0 causes Timer 1 overflow to be used for the receive clock.

Transmit clock enable. When set, causes the serial port to use Timer 2 overflow pulses for its transmit clock in serial port Modes 1 and 3. TCLK = 0 causes Timer 1 overflows to be used for the transmit clock.

Timer 2 external enable. When set, allows a capture or reload to occur as a result of a negative transition on T2EX if Timer 2 is not being used to clock the serial port. EXEN2 = 0 causes Timer 2 to ignore events at T2EX.

Timer or counter select for Timer 2. C/T2 = 0 for timer function. C/T2 = 1 for external event counter (falling edge triggered).

Capture/Reload select. CP/RL2 = 1 causes captures to occur on negative transitions at T2EX if EXEN2 = 1. CP/RL2 = 0 causes automatic reloads to occur when Timer 2 overflows or negative transitions occur at T2EX when EXEN2 = 1. When either RCLK or TCLK = 1, this bit is ignored and the timer is forced to auto-reload on Timer 2 overflow.

CP/RL2

1921C–MICRO–3/05

Table 5-3. AUXR: Auxiliary Register

AUXR Address = 8EH Reset Value = XXX00XX0B

Not Bit Addressable

– – – WDIDLE DISRTO – – DISALE

Bit 7 6 5 4 3 2 1 0

– Reserved for future expansion

DISALE Disable/Enable ALE

DISALE Operating Mode

0 ALE is emitted at a constant rate of 1/6 the oscillator frequency

1 ALE is active only during a MOVX or MOVC instruction

DISRTO Disable/Enable Reset out

DISRTO Operating Mode

0 Reset pin is driven High after WDT times out

1 Reset pin is input only

WDIDLE Disable/Enable WDT in IDLE mode

WDIDLE Operating Mode

0 WDT continues to count in IDLE mode

1 WDT halts counting in IDLE mode

Table 5-4. AUXR1: Auxiliary Register 1

AUXR1 Address = A2H Reset Value = XXXXXXX0B

Not Bit Addressable

––– – – – –DPS

Bit 7 6 5 4 3 2 1 0

– Reserved for future expansion

DPS Data Pointer Register Select

DPS

0 Selects DPTR Registers DP0L, DP0H

1 Selects DPTR Registers DP1L, DP1H

AT89C55WD

1921C–MICRO–3/05

6. Memory Organization

The MCS-51 devices have a separate address space for Program and Data Memory. Up to 64 Kbytes each of external Program and Data Memory can be addressed.

6.1 Program Memory

If the EA pin is connected to GND, all program fetches are directed to external memory.

AT89C55WD

6.2 Data Memory

On the AT89C55WD, if EA 4FFFH are directed to internal memory and fetches to addresses 5000H through FFFFH are to external memory.

The AT89C55WD implements 256 bytes of on-chip RAM. The upper 128 bytes occupy a parallel address space to the Special Function Registers. That means the upper 128 bytes have the same addresses as the SFR space but are physically separate from SFR space.

When an instruction accesses an internal location above address 7FH, the address mode used in the instruction specifies whether the CPU accesses the upper 128 bytes of RAM or the SFR space. Instructions that use direct addressing access SFR space.

For example, the following direct addressing instruction accesses the SFR at location 0A0H (which is P2).

MOV 0A0H, #data

Instructions that use indirect addressing access the upper 128 bytes of RAM. For example, the following indirect addressing instruction, where R0 contains 0A0H, accesses the data byte at address 0A0H, rather than P2 (whose address is 0A0H).

MOV @R0, #data

Note that stack operations are examples of indirect addressing, so the upper 128 bytes of data RAM are available as stack space.

is connected to VCC, program fetches to addresses 0000H through

7. Hardware Watchdog Timer (One-time Enabled with Reset-out)

The WDT is intended as a recovery method in situations where the CPU may be subjected to software upsets. The WDT consists of a 13-bit counter and the WatchDog Timer Reset (WDTRST) SFR. The WDT is defaulted to disable from exiting reset. To enable the WDT, a user must write 01EH and 0E1H in sequence to the WDTRST register (SFR location 0A6H). When the WDT is enabled, it will increment every machine cycle while the oscillator is running. The WDT time-out period is dependent on the external clock frequency. There is no way to disable the WDT except through reset (either hardware reset or WDT overflow reset). When WDT overflows, it will drive an output RESET HIGH pulse at the RST pin.

1921C–MICRO–3/05

8. Using the WDT

To enable the WDT, a user must write 01EH and 0E1H in sequence to the WDTRST register (SFR location 0A6H). When the WDT is enabled, the user needs to service it by writing 01EH and 0E1H to WDTRST to avoid a WDT overflow. The 13-bit counter overflows when it reaches 8191 (1FFFH), and this will reset the device. When the WDT is enabled, it will increment every machine cycle while the oscillator is running. This means the user must re-initialize the WDT at least every 8191 machine cycles. To re-initialize the WDT the user must write 01EH and 0E1H to WDTRST. WDTRST is a write-only register. The WDT counter cannot be read or written. When WDT overflows, it will generate an output RESET pulse at the RST pin. The RESET pulse duration is 98xTOSC, where TOSC=1/FOSC. To make the best use of the WDT, it should be serviced in those sections of code that will periodically be executed within the time required to prevent a WDT reset.

9. WDT During Power-down and Idle

In Power-down mode the oscillator stops, which means the WDT also stops. While in Powerdown mode, the user does not need to service the WDT. There are two methods of exiting Power-down mode: by a hardware reset or via a level-activated external interrupt which is enabled prior to entering Power-down mode. When Power-down is exited with hardware reset, servicing the WDT should occur as it normally does whenever the AT89C55WD is reset. Exiting Power-down with an interrupt is significantly different. The interrupt is held low long enough for the oscillator to stabilize. When the interrupt is brought high, the interrupt is serviced. To prevent the WDT from resetting the device while the interrupt pin is held low, the WDT is not started until the interrupt is pulled high. It is suggested that the WDT be reset during the interrupt service for the interrupt used to exit Power-down.

10. UART

11. Timer 0 and 1

To ensure that the WDT does not overflow within a few states of exiting Power-down, it is best to reset the WDT just before entering Power-down.

Before going into the IDLE mode, the WDIDLE bit in SFR AUXR is used to determine whether the WDT continues to count if enabled. The WDT keeps counting during IDLE (WDIDLE bit = 0) as the default state. To prevent the WDT from resetting the AT89C55WD while in IDLE mode, the user should always set up a timer that will periodically exit IDLE, service the WDT, and reenter IDLE mode.

With WDIDLE bit enabled, the WDT will stop to count in IDLE mode and resumes the count upon exit from IDLE.

The UART in the AT89C55WD operates the same way as the UART in the AT89C51 and AT89C52. For more detailed information on the UART operation, please click on the document link below:

http://www.atmel.com/dyn/resources/prod_documents/DOC4316.PDF

Timer 0 and Timer 1 in the AT89C55WD operate the same way as Timer 0 and Timer 1 in the AT89C51 and AT89C52. For further information on the timers’ operation, please click on the document link below:

http://www.atmel.com/dyn/resources/prod_documents/DOC4316.PDF

AT89C55WD

1921C–MICRO–3/05

12. Timer 2

AT89C55WD

Timer 2 is a 16-bit Timer/Counter that can operate as either a timer or an event counter. The type of operation is selected by bit C/T2 three operating modes: capture, auto-reload (up or down counting), and baud rate generator. The modes are selected by bits in T2CON, as shown in Table 5-2.

Timer 2 consists of two 8-bit registers, TH2 and TL2. In the Timer function, the TL2 register is incremented every machine cycle. Since a machine cycle consists of 12 oscillator periods, the count rate is 1/12 of the oscillator frequency.

Table 12-1. Timer 2 Operating Modes

RCLK +TCLK CP/RL2 TR2 MODE

0 0 1 16-bit Auto-Reload

0 1 1 16-bit Capture

1 X 1 Baud Rate Generator

X X 0 (Off)

In the Counter function, the register is incremented in response to a 1-to-0 transition at its corresponding external input pin, T2. In this function, the external input is sampled during S5P2 of every machine cycle. When the samples show a high in one cycle and a low in the next cycle, the count is incremented. The new count value appears in the register during S3P1 of the cycle following the one in which the transition was detected. Since two machine cycles (24 oscillator periods) are required to recognize a 1-to-0 transition, the maximum count rate is 1/24 of the oscillator frequency. To ensure that a given level is sampled at least once before it changes, the level should be held for at least one full machine cycle.

in the SFR T2CON (shown in Table 5-2). Timer 2 has

12.1 Capture Mode

In the capture mode, two options are selected by bit EXEN2 in T2CON. If EXEN2 = 0, Timer 2 is a 16-bit timer or counter which upon overflow sets bit TF2 in T2CON. This bit can then be used to generate an interrupt. If EXEN2 = 1, Timer 2 performs the same operation, but a 1-to-0 transition at external input T2EX also causes the current value in TH2 and TL2 to be captured into RCAP2H and RCAP2L, respectively. In addition, the transition at T2EX causes bit EXF2 in T2CON to be set. The EXF2 bit, like TF2, can generate an interrupt. The capture mode is illustrated in Figure 12-1.

12.2 Auto-reload (Up or Down Counter)

Timer 2 can be programmed to count up or down when configured in its 16-bit auto-reload mode. This feature is invoked by the DCEN (Down Counter Enable) bit located in the SFR T2MOD (see Table 12-2). Upon reset, the DCEN bit is set to 0 so that timer 2 will default to count up. When DCEN is set, Timer 2 can count up or down, depending on the value of the T2EX pin.

1921C–MICRO–3/05

+ 24 hidden pages