ATMEL AT89C51AC3 User Manual

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Features

• 80C51 Core Architecture

• 256 Bytes of On-chip RAM

• 2048 Bytes of On-chip ERAM

• 64K Bytes of On-chip Flash Memory

– Data Retention: 10 Years at 85°C – Read/Write Cycle: 100K

• Boot Code Section with Independent Lock Bits

• 2K Bytes of On-chip Flash for Bootloader

• In-System Programming by On-Chip UART Boot Program and IAP Capability

• 2K Bytes of On-chip EEPROM

Read/Write Cycle: 100K

• Integrated Power Monitor (POR: PFD) To Supervise Internal Power Supply

• 14-sources 4-level Interrupts

• Three 16-bit Timers/Counters

• Full Duplex UART Compatible 80C51

• High-speed Architecture

– In Standard Mode:

40 MHz (Vcc 3V to 5.5V, both Internal and external code execution) 60 MHz (Vcc 4.5V to 5.5V and Internal Code execution only)

– In X2 mode (6 Clocks/machine cycle)

20 MHz (Vcc 3V to 5.5V, both Internal and external code execution) 30 MHz (Vcc 4.5V to 5.5V and Internal Code execution only)

• Five Ports: 32 + 4 Digital I/O Lines

• Five-channel 16-bit PCA with

– PWM (8-bit) – High-speed Output – Timer and Edge Capture

• Double Data Pointer

• 21-bit WatchDog Timer (7 Programmable Bits)

• A 10-bit Resolution Analog to Digital Converter (ADC) with 8 Multiplexed Inputs

• SPI Interface (PLCC52 and VPFP64 packages only)

• On-chip Emulation Logic (Enhanced Hook System)

• Power Saving Modes

– Idle Mode – Power-down Mode

• Power Supply: 3 volts to 5.5 volts

• Temperature Range: Industrial (-40° to +85°C)

• Packages: VQFP44, PLCC44, VQFP64, PLCC52

Enhanced 8-bit Microcontroller with 64KB Flash Memory

AT89C51AC3

Description

The AT89C51AC3 is a high performance Flash version of the 80C51 single chip 8-bit microcontrollers.

In X2 mode a maximum external clock rate of 20 MHz reaches a 300 ns cycle time.

Besides the AT89C51AC3 provides 64K Bytes of Flash memory including In-System Programming (ISP) and IAP, 2K Bytes Boot Flash Memory, 2K Bytes EEPROM and 2048 byte ERAM.

Primary attention is paid to the reduction of the electro-magnetic emission of AT89C51AC3.

Rev. 4383D–8051–02/08

AT89C51AC3

Block Diagram

Timer 0

INT

RAM

256x8

RxD

TxD

PSEN

ALE

XTAL2

XTAL1

UART

CPU

Timer 1

INT1

Ctrl

INT0

C51

CORE

Port 0P0Port 1

Port 2

Port 3

Parallel I/O Ports and Ext. Bus

P1(1)

ERAM

2048

IB-bus

PCA

RESET

Watch

Dog

PCA

ECI

Vss

Vcc

Timer2

T2EX

Port 4

P4(2)

Emul

Unit

10 bit

ADC

Flash

64k x

Boot

loader

2kx8

PROM

2kx8

SPI

Interface

MOSI

SCK

MISO

Notes: 1. 8 analog Inputs/8 Digital I/O

2. 5-Bit I/O Port

4383D–8051–02/08

Pin Configuration

PLCC44

P1.3/AN3/CEX0

P1.2/AN2/ECI

P1.1/AN1/T2EX

P1.0/AN 0/T2

VAREF

VAGND

RESET

VSS

VCC

XTAL1

XTAL2

P3.7/RD

P4.0

P4.1

P2.7/A15

P2.6/A14

P2.5/A13

P2.4/A12

P2.3/A11

P2.2/A10

P2.1/A9

P3.6/WR

39 38 37 36 35 34 33 32

7 8 9 10 11 12 13 14

1819202122232425262728

65432

4443424140

ALE PSEN P0.7/AD7 P0.6/AD6 P0.5/AD5

P0.2/AD2

P0.3/AD3

P0.4/AD4

P0.1/AD1 P0.0/AD0 P2.0/A8

P1.4/AN4/CEX1 P1.5/AN5/CEX2 P1.6/AN6/CEX3 P1.7/AN7/CEX4

P3.0/RxD

P3.1/TxD P3.2/INT0 P3.3/INT1

P3.4/T0 P3.5/T1

43 42 41 40 3944

38 37 36 35 34

12 13 17161514 201918 21 22

33 32

26 25

VQFP44

P1.4/AN4/CEX1 P1.5/AN5/CEX2 P1.6/AN6/CEX3 P1.7/AN7/CEX4

P3.0/RxD

P3.1/TxD P3.2/INT0 P3.3/INT1

P3.4/T0 P3.5/T1

ALE PSEN P0.7/AD7 P0.6/AD6 P0.5/AD5

P0.2 /AD2

P0.3 /AD3

P0.4 /AD4

P0.1 /AD1 P0.0 /AD0 P2.0/A8

P1.3/AN3/CEX0

P1.2/AN2/ECI

P1.1/AN1/T2EX

P1.0/AN 0/T2

VAREF

VAGND

RESET

VSS

VCC

XTAL1

XTAL2

P3.7/RD

P4.0

P4.1

P2.7/A15

P2.6/A14

P2.5/A13

P2.4/A12

P2.3/A11

P2.2/A10

P2.1/A9

P3.6/WR

AT89C51AC3

4383D–8051–02/08

AT89C51AC3

21 22 26252423 292827 30 31

5 4 3 2 1 6

52 51 50 49 48

40 39

PLCC52

7 47

32 33

P1.3/AN3/CEX0

P1.2/AN2/ECI

P1.1/AN1/T2EX

P1.0/AN 0/T2

VAREF

VAGND

RESET

VSS

VCC

XTAL1

XTAL2

TESTI

P1.4/AN4/CEX1 P1.5/AN5/CEX2 P1.6/AN6/CEX3 P1.7/AN7/CEX4

P3.0/RxD

P3.1/TxD P3.2/INT0 P3.3/INT1

P3.4/T0

P3.5/T1/SS

P4.3/SCK

ALE PSEN P0.7/AD7 P0.6/AD6

P0.5/AD5

P0.2 /AD2

P0.3 /AD3

P0.4 /AD4

P0.1 /AD1

P0.0 /AD0

P2.0/A8

P4.4/MOSI

P3.7/RD

P4.0

P4.1

P2.7/A15

P2.6/A14

P2.5/A13

P2.4/A12

P2.3/A11

P2.2/A10

P2.1/A9

P3.6/WR

P4.2/MISO

TESTI must be connected to VSS

VCC

5453525150

VQFP64

P1.3/AN3/CEX0

P1.2/AN2/ECI

P1.1/AN1/T2EX

P1.0/AN0/T2

VAREF

VAGND

RESET

VSS

P3.7/RD

P4.0

P4.1

P2.7/A15

P2.6/A14

NCNCNC

P3.6/WR

48 47 46 45 44 43 42 41

1 2 3 4 5 6 7 8

171819202122232425

646362616059585756

NC ALE PSEN P0.7/AD7 P0.6/AD6

P0.5/AD5

NC P0.4/AD4

P1.4/AN4/CEX1

NC P1.5/AN5/CEX2 P1.6/AN6/CEX3 P1.7/AN7/CEX4

P3.0/RxD

11 12 13

P4.3/SCK

P3.1/TxD P3.2/INT0 P3.3/INT1

P3.4/T0

P3.5/T1/SS

38 37 36

P0.1/AD1

P0.2/AD2

P0.3/AD3

P4.4/MOSI P0.0/AD0 P2.0/A8

P2.5/A13

P2.4/A12

P2.3/A11

P2.2/A10

P2.1/A9

P4.2/MISO

2728293031

TESTI

VCC

XTAL1

XTAL2

VCC

TESTI must be connected to VSS

4383D–8051–02/08

Pin Name Type Description

VSS GND Circuit ground

TESTI I Must be connected to VSS

VCC Supply Voltage

VAREF Reference Voltage for ADC

VAGND Reference Ground for ADC

P0.0:7 I/O Port 0:

Is an 8-bit open drain bi-directional I/O port. Port 0 pins that have 1’s written to them float, and in this state can be used as high-impedance inputs. Port 0 is also the multiplexed low-order address and data bus during accesses to external Program and Data Memory. In this application it uses strong internal pull-ups when emitting 1’s. Port 0 also outputs the code Bytes during program validation. External pull-ups are required during program verification.

AT89C51AC3

P1.0:7 I/O Port 1:

Is an 8-bit bi-directional I/O port with internal pull-ups. Port 1 pins can be used for digital input/output or as analog inputs for the Analog Digital Converter (ADC). Port 1 pins that have 1’s written to them are pulled high by the internal pull-up transistors and can be used as inputs in this state. As inputs, Port 1 pins that are being pulled low externally will be the source of current (IIL, see section "Electrical Characteristic") because of the internal pull-ups. Port 1 pins are assigned to be used as analog inputs via the ADCCF register (in this case the internal pull-ups are disconnected). As a secondary digital function, port 1 contains the Timer 2 external trigger and clock input; the PCA external clock input and the PCA module I/O.

P1.0/AN0/T2 Analog input channel 0, External clock input for Timer/counter2.

P1.1/AN1/T2EX Analog input channel 1, Trigger input for Timer/counter2.

P1.2/AN2/ECI Analog input channel 2, PCA external clock input.

P1.3/AN3/CEX0 Analog input channel 3, PCA module 0 Entry of input/PWM output.

P1.4/AN4/CEX1 Analog input channel 4, PCA module 1 Entry of input/PWM output.

P1.5/AN5/CEX2 Analog input channel 5, PCA module 2 Entry of input/PWM output.

P1.6/AN6/CEX3 Analog input channel 6, PCA module 3 Entry of input/PWM output.

P1.7/AN7/CEX4 Analog input channel 7, PCA module 4 Entry ot input/PWM output. Port 1 receives the low-order address byte during EPROM programming and program verification. It can drive CMOS inputs without external pull-ups.

P2.0:7 I/O Port 2:

4383D–8051–02/08

Is an 8-bit bi-directional I/O port with internal pull-ups. Port 2 pins that have 1’s written to them are pulled high by the internal pull-ups and can be used as inputs in this state. As inputs, Port 2 pins that are being pulled low externally will be a source of current (IIL, see section "Electrical Characteristic") because of the internal pull-ups. Port 2 emits the high-order address byte during accesses to the external Program Memory and during accesses to external Data Memory that uses 16-bit addresses (MOVX @DPTR). In this application, it uses strong internal pull-ups when emitting 1’s. During accesses to external Data Memory that use 8 bit addresses (MOVX @Ri), Port 2 transmits the contents of the P2 special function register. It also receives high-order addresses and control signals during program validation. It can drive CMOS inputs without external pull-ups.

AT89C51AC3

Pin Name Type Description

P3.0:7 I/O Port 3:

Is an 8-bit bi-directional I/O port with internal pull-ups. Port 3 pins that have 1’s written to them are pulled high by the internal pull-up transistors and can be used as inputs in this state. As inputs, Port 3 pins that are being pulled low externally will be a source of current (IIL, see section "Electrical Characteristic") because of the internal pull-ups. The output latch corresponding to a secondary function must be programmed to one for that function to operate (except for TxD and WR). The secondary functions are assigned to the pins of port 3 as follows:

P3.0/RxD: Receiver data input (asynchronous) or data input/output (synchronous) of the serial interface

P3.1/TxD: Transmitter data output (asynchronous) or clock output (synchronous) of the serial interface

P3.2/INT0: External interrupt 0 input/timer 0 gate control input

P3.3/INT1: External interrupt 1 input/timer 1 gate control input

P3.4/T0: Timer 0 counter input

P3.5/T1/SS: Timer 1 counter input

SPI Slave Select

P3.6/WR: External Data Memory write strobe; latches the data byte from port 0 into the external data memory

P3.7/RD: External Data Memory read strobe; Enables the external data memory. It can drive CMOS inputs without external pull-ups.

P4.0:4 I/O Port 4:

Is an 2-bit bi-directional I/O port with internal pull-ups. Port 4 pins that have 1’s written to them are pulled high by the internal pull-ups and can be used as inputs in this state. As inputs, Port 4 pins that are being pulled low externally will be a source of current (IIL, on the datasheet) because of the internal pull-up transistor. The secondary functions are assigned to the 5 pins of port 4 as follows: P4.0: Regular Port I/O

P4.1: Regular Port I/O

P4.2/MISO:

Master Input Slave Output of SPI controller P4.3/SCK:

Serial Clock of SPI controller P4.4/MOSI: Master Ouput Slave Input of SPI controller

It can drive CMOS inputs without external pull-ups.

4383D–8051–02/08

Pin Name Type Description

Reset:

RESET I/O

ALE O

PSEN O

EA I

XTAL1 I

A high level on this pin during two machine cycles while the oscillator is running resets the device. An internal pull-down resistor to VSS permits power-on reset using only an external capacitor to VCC.

ALE:

An Address Latch Enable output for latching the low byte of the address during accesses to the external memory. The ALE is activated every 1/6 oscillator periods (1/3 in X2 mode) except during an external data memory access. When instructions are executed from an internal Flash (EA = 1), ALE generation can be disabled by the software.

PSEN:

The Program Store Enable output is a control signal that enables the external program memory of the bus during external fetch operations. It is activated twice each machine cycle during fetches from the external program memory. However, when executing from of the external program memory two activations of PSEN are skipped during each access to the external Data memory. The PSEN is not activated for internal fetches.

EA:

When External Access is held at the high level, instructions are fetched from the internal Flash. When held at the low level, AT89C51AC3 fetches all instructions from the external program memory

XTAL1:

Input of the inverting oscillator amplifier and input of the internal clock generator circuits. To drive the device from an external clock source, XTAL1 should be driven, while XTAL2 is left unconnected. To operate above a frequency of 16 MHz, a duty cycle of 50% should be maintained.

AT89C51AC3

XTAL2 O

XTAL2:

Output from the inverting oscillator amplifier.

I/O Configurations

Port 1, Port 3 and Port 4

Each Port SFR operates via type-D latches, as illustrated in Figure 1 for Ports 3 and 4. A CPU "write to latch" signal initiates transfer of internal bus data into the type-D latch. A CPU "read latch" signal transfers the latched Q output onto the internal bus. Similarly, a "read pin" signal transfers the logical level of the Port pin. Some Port data instructions activate the "read latch" signal while others activate the "read pin" signal. Latch instructi ons are referred to as Read-Modify-Write instructions. Each I/ O line may be independently programmed as input or output.

Figure 1 shows the structure of Ports 1 and 3, which have internal pull-ups. An external source can pull the pin low. Each Port pin can be configured either for general-purpose I/O or for its alternate input output function.

To use a pin for general-purpose output, set or clear the corresponding bit in the Px register (x = 1,3 or 4). To use a pin for general-purpose input, set the bit in the Px register. This turns off the output FET drive.

To configure a pin for its alternate function, set the bit in the Px register. When the latch is set, the "alternate output function" signal controls the output level (see Figure 1). The operation of Ports 1, 3 and 4 is discussed further in the "quasi-Bidirectional Port Operation" section.

4383D–8051–02/08

AT89C51AC3

Figure 1. Port 1, Port 3 and Port 4 Structure

QP1.X

LATCH

INTERNAL

WRITE TO LATCH

READ PIN

READ LATCH

P1.x

P3.X P4.X

ALTERNATE OUTPUT FUNCTION

VCC

INTERNAL PULL-UP (1)

ALTERNATE INPUT FUNCTION

P3.x P4.x

BUS

P0.X

LATCH

INTERNAL

WRITE TO LATCH

READ PIN

READ LATCH

P0.x (1)

ADDRESS LOW/ DATA

CONTROL

VDD

BUS

(2)

Note: The internal pull-up can be disabled on P1 when analog function is selected.

Port 0 and Port 2

Ports 0 and 2 are used for general-purpose I/O or as the external address/data bus. Port 0, shown in Figure 3, differs from the other Ports in not having internal pull-ups. Figure 3 shows the structure of Port 2. An external source can pull a Port 2 pin low.

To use a pin for general-purpose output, set or clear the corresponding bit in the Px register (x = 0 or 2). To use a pin for general-purpose input, set the bit in the Px register to turn off the output driver FET.

Figure 2. Port 0 Structure

Notes: 1. Port 0 is precluded from use as general-purpose I/O Ports when used as

address/data bus drivers.

2. Port 0 internal strong pull-ups assist the logic-one output for memory bus cycles only. Except for these bus cycles, the pull-up FET is off, Port 0 outputs are open-drain.

4383D–8051–02/08

AT89C51AC3

P2.X

LATCH

INTERNAL

WRITE TO LATCH

READ PIN

READ LATCH

P2.x (1)

ADDRESS HIGH/

CONTROL

BUS

VDD

INTERNAL PULL-UP (2)

Figure 3. Port 2 Structure

Notes: 1. Port 2 is precluded from use as general-purpose I/O Ports when as address/data bus

drivers.

2. Port 2 internal strong pull-ups FET (P1 in FiGURE) assist the logic-one output for memory bus cycle.

Read-Modify-Write Instructions

When Port 0 and Port 2 are used for an external memory cycle, an internal control signal switches the output-driver input from the latch output to the internal address/data line.

Some instructions read the latch data rather than the pin data. The latch based instructions read the data, modify the data and then rewrite the latch. These are called "ReadModify-Write" instructions. Below is a complete list of these special instructions (see Table ). When the destination operand is a Port or a Port bit, these instructions read the latch rather than the pin:

Instruction Description Example

ANL logical AND ANL P1, A

ORL logical OR ORL P2, A

XRL logical EX-OR XRL P3, A

JBC jump if bit = 1 and clear bit JBC P1.1, LABEL

CPL complement bit CPL P3.0

INC increment INC P2

DEC decrement DEC P2

It is not obvious the last three instructions in this list are Read-Modify-Write instructions.

DJNZ decrement and jump if not zero DJNZ P3, LABEL

MOV Px.y, C move carry bit to bit y of Port x MOV P1.5, C

CLR Px.y clear bit y of Port x CLR P2.4

SET Px.y set bit y of Port x SET P3.3

These instructions read the port (all 8 bits), modify the specifically addressed bit and

4383D–8051–02/08

AT89C51AC3

write the new byte back to the latch. These Read-Modify-Write instructions are directed

READ PIN

INPUT DATA

P1.x

OUTPUT DATA

2 Osc. PERIODS

p1(1)

VCCVCCVCC

P2.x P3.x P4.x

to the latch rather than the pin in order to avoid possible misinterpretation of voltage (and therefore, logic) levels at the pin. For example, a Port bit used to drive the base of an external bipolar transistor can not rise above the transistor’s base-emitter junction voltage (a value lower than VIL). With a logic one written to the bit, attempts by the CPU to read the Port at the pin are misinterpreted as logic zero. A read of the latch rather than the pins returns the correct logic-one value.

Quasi-Bidirectional Port Operation

Port 1, Port 2, Port 3 and Port 4 have fixed internal pull-ups and are referred to as "quasi-bidirectional" Ports. When configured as an input, the pin impedance appears as logic one and sources current in response to an external logic zero condition. Port 0 is a "true bidirectional" pin. The pins float when configured as input. Resets write logic one to all Port latches. If logical zero is subsequently written to a Port latch, it can be returned to input conditions by a logical one written to the latch.

Note: Port latch values change near the end of Read-Modify-Write instruction cycles. Output

buffers (and therefore the pin state) update early in the instruction after Read-ModifyWrite instruction cycle.

Logical zero-to-one transitions in Port 1, Port 2, Port 3 and Port 4 use an additional pullup (p1) to aid this logic transition (see Figure 4.). This increases switch speed. This extra pull-up sources 100 times normal internal circuit current during 2 oscillator clock periods. The internal pull-ups are field-effect transistors rather than linear resistors. Pullups consist of three p-channel FET (pFET) devices. A pFET is on when the gate senses logical zero and off when the gate senses logical one. pFET #1 is turned on for two oscillator periods immediately after a zero-to-one transition in the Port latch. A logical one at the Port pin turns on pFET #3 (a weak pull-up) through the inverter. This inverter and pFET pair form a latch to drive logical one. pFET #2 is a very weak pull-up switched on whenever the associated nFET is switched off. This is traditional CMOS switch convention. Current strengths are 1/10 that of pFET #3.

Figure 4. Internal Pull-Up Configurations

Note: Port 2 p1 assists the logic-one output for memory bus cycles.

4383D–8051–02/08

AT89C51AC3

SFR Mapping

The Special Function Registers (SFRs) of the AT89C51AC3 fall into the following categories:

Mnemonic Add Name 7 6 5 4 3 2 1 0

ACC E0h Accumulator – – – – – – – –

B F0h B Register – – – – – – – –

PSW D0h Program Status Word CY AC F0 RS1 RS0 OV F1 P

SP 81h Stack Pointer – – – – – – – –

Data Pointer Low

DPL 82h

DPH 83h

Mnemonic Add Name 7 6 5 4 3 2 1 0

P0 80h Port 0 – – – – – – – –

P1 90h Port 1 – – – – – – – –

byte

LSB of DPTR

Data Pointer High byte

MSB of DPTR

– – – – – – – –

P2 A0h Port 2 – – – – – – – –

P3 B0h Port 3 – – – – – – – –

P4 C0h Port 4 (x5) – – –

Mnemonic Add Name 7 6 5 4 3 2 1 0

TH0 8Ch

TL0 8Ah

TH1 8Dh

TL1 8Bh

TH2 CDh

TL2 CCh

TCON 88h

Timer/Counter 0 High byte

Timer/Counter 0 Low byte

Timer/Counter 1 High byte

Timer/Counter 1 Low byte

Timer/Counter 2 High byte

Timer/Counter 2 Low byte

Timer/Counter 0 and 1 control

– – – – – – – –

TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0

P4.4 / MOSI

P4.3 /

SCK

P4.2 / MISO

P4.1 P4.0

TMOD 89h

4383D–8051–02/08

Timer/Counter 0 and 1 Modes

GATE1 C/T1# M11 M01 GATE0 C/T0# M10 M00

AT89C51AC3

Mnemonic Add Name 7 6 5 4 3 2 1 0

T2CON C8h

T2MOD C9h

RCAP2H CBh

RCAP2L CAh

WDTRST A6h

WDTPRG A7h

Mnemonic Add Name 7 6 5 4 3 2 1 0

SCON 98h Serial Control FE/SM0 SM1 SM2 REN TB8 RB8 TI RI

SBUF 99h Serial Data Buffer – – – – – – – –

SADEN B9h Slave Address Mask – – – – – – – –

SADDR A9h Slave Address – – – – – – – –

Timer/Counter 2 control

Timer/Counter 2 Mode

Timer/Counter 2 Reload/Capture High byte

Timer/Counter 2 Reload/Capture Low byte

WatchDog Timer Reset

WatchDog Timer Program

TF2 EXF2 RCLK TCLK EXEN2 TR2 C/T2# CP/RL2#

– – – – – – T2OE DCEN

– – – – – – – –

– – – – – S2 S1 S0

Mnemonic

CCON D8h PCA Timer/Counter Control CF CR – CCF4 CCF3 CCF2 CCF1 CCF0

CMOD D9h PCA Timer/Counter Mode CIDL WDTE – – – CPS1 CPS0 ECF

CL E9h PCA Timer/Counter Low byte – – – – – – – –

CH F9h PCA Timer/Counter High byte – – – – – – – –

CCAPM0

CCAPM1

CCAPM2

CCAPM3

CCAPM4

CCAP0H

CCAP1H

CCAP2H

CCAP3H

CCAP4H

CCAP0L

CCAP1L

CCAP2L

CCAP3L

CCAP4L

Add Name 7 6 5 4 3 2 1 0

DAh

PCA Timer/Counter Mode 0

DBh

PCA Timer/Counter Mode 1

DCh

PCA Timer/Counter Mode 2

DDh

PCA Timer/Counter Mode 3

DEh

PCA Timer/Counter Mode 4

FAh

PCA Compare Capture Module 0 H

FBh

PCA Compare Capture Module 1 H

FCh

PCA Compare Capture Module 2 H

FDh

PCA Compare Capture Module 3 H

FEh

PCA Compare Capture Module 4 H

EAh

PCA Compare Capture Module 0 L

EBh

PCA Compare Capture Module 1 L

ECh

PCA Compare Capture Module 2 L

EDh

PCA Compare Capture Module 3 L

EEh

PCA Compare Capture Module 4 L

CCAP0H7

CCAP1H7

CCAP2H7

CCAP3H7

CCAP4H7

CCAP0L7

CCAP1L7

CCAP2L7

CCAP3L7

CCAP4L7

–

ECOM0

ECOM1

ECOM2

ECOM3

ECOM4

CCAP0H6

CCAP1H6

CCAP2H6

CCAP3H6

CCAP4H6

CCAP0L6

CCAP1L6

CCAP2L6

CCAP3L6

CCAP4L6

CAPP0

CAPP1

CAPP2

CAPP3

CAPP4

CCAP0H5

CCAP1H5

CCAP2H5

CCAP3H5

CCAP4H5

CCAP0L5

CCAP1L5

CCAP2L5

CCAP3L5

CCAP4L5

CAPN0

CAPN1

CAPN2

CAPN3

CAPN4

CCAP0H4

CCAP1H4

CCAP2H4

CCAP3H4

CCAP4H4

CCAP0L4

CCAP1L4

CCAP2L4

CCAP3L4

CCAP4L4

MAT0

MAT1

MAT2

MAT3

MAT4

CCAP0H3

CCAP1H3

CCAP2H3

CCAP3H3

CCAP4H3

CCAP0L3

CCAP1L3

CCAP2L3

CCAP3L3

CCAP4L3

TOG0

TOG1

TOG2

TOG3

TOG4

CCAP0H2

CCAP1H2

CCAP2H2

CCAP3H2

CCAP4H2

CCAP0L2

CCAP1L2

CCAP2L2

CCAP3L2

CCAP4L2

PWM0

PWM1

PWM2

PWM3

PWM4

CCAP0H1

CCAP1H1

CCAP2H1

CCAP3H1

CCAP4H1

CCAP0L1

CCAP1L1

CCAP2L1

CCAP3L1

CCAP4L1

ECCF0

ECCF1

ECCF2

ECCF3

ECCF4

CCAP0H0

CCAP1H0

CCAP2H0

CCAP3H0

CCAP4H0

CCAP0L0

CCAP1L0

CCAP2L0

CCAP3L0

CCAP4L0

4383D–8051–02/08

AT89C51AC3

Mnemonic Add Name 7 6 5 4 3 2 1 0

IEN0 A8h

IEN1 E8h

IPL0 B8h

IPH0 B7h

IPL1 F8h

IPH1 F7h

Mnemonic Add Name 7 6 5 4 3 2 1 0

ADCON F3h ADC Control – PSIDLE ADEN ADEOC ADSST SCH2 SCH1 SCH0

ADCF F6h ADC Configuration CH7 CH6 CH5 CH4 CH3 CH2 CH1 CH0

ADCLK F2h ADC Clock – – – PRS4 PRS3 PRS2 PRS1 PRS0

ADDH F5h ADC Data High byte ADAT9 ADAT8 ADAT7 ADAT6 ADAT5 ADAT4 ADAT3 ADAT2

ADDL F4h ADC Data Low byte – – – – – – ADAT1 ADAT0

Interrupt Enable Control 0

Interrupt Enable Control 1

Interrupt Priority Control Low 0

Interrupt Priority Control High 0

Interrupt Priority Control Low 1

Interrupt Priority Control High1

EA EC ET2 ES ET1 EX1 ET0 EX0

– – – – ESPI – EADC –

– PPC PT2 PS PT1 PX1 PT0 PX0

– PPCH PT2H PSH PT1H PX1H PT0H PX0H

– – – – SPIL – PADCL –

– – – – SPIH – PADCH –

Mnemonic Add Name 7 6 5 4 3 2 1 0

SPCON D4h SPI Control SPR2 SPEN SSDIS MSTR CPOL CPHA SPR1 SPR0

SPSCR D5h

SPDAT D6h SPI Data – – – – – – – –

Mnemonic Add Name 7 6 5 4 3 2 1 0

PCON 87h Power Control SMOD1 SMOD0 – POF GF1 GF0 PD IDL

AUXR 8Eh Auxiliary Register 0 DPU VPFDP M0 XRS2 XRS1 XRS0 EXTRAM A0

AUXR1 A2h Auxiliary Register 1 – – ENBOOT – GF3 0 – DPS

CKCON0 8Fh Clock Control 0 – WDX2 PCAX2 SIX2 T2X2 T1X2 T0X2 X2

CKCON1 9Fh Clock Control 1 – – – – – – – SPIX2

FCON D1h Flash Control FPL3 FPL2 FPL1 FPL0 FPS FMOD1 FMOD0 FBUSY

EECON D2h EEPROM Contol EEPL3 EEPL2 EEPL1 EEPL0 – – EEE EEBUSY

FSTA D3 Flash Status - - - - - - SEQERR FLOAD

SPI Status and Control

SPIF – OVR MODF SPTE UARTM SPTEIE MOFIE

4383D–8051–02/08

AT89C51AC3

Table 1. SFR Mapping

(2)

0/8

1/9 2/A 3/B 4/C 5/D 6/E 7/F

F8h

F0h

E8h

E0h

D8h

D0h

C8h

C0h

B8h

B0h

A8h

IPL1

xxxx x0x0

0000 0000

IEN1

xxxx x0x0

ACC

0000 0000

CCON

0000 0000

PSW

0000 0000

T2CON

0000 0000

xxx1 1111

IPL0

x000 0000

1111 1111

IEN0

0000 0000

CMOD

00xx x000

FCON

0000 0000

T2MOD

xxxx xx00

SADEN

0000 0000

SADDR

0000 0000

CCAP0H

0000 0000

ADCLK

xxx0 0000

CCAP0L

0000 0000

CCAPM0

x000 0000

EECON

xxxx xx00

RCAP2L

0000 0000

CCAP1H

0000 0000

ADCON

x000 0000

CCAP1L

0000 0000

CCAPM1

x000 0000

FSTA

xxxx xx00

RCAP2H

0000 0000

CCAP2H

0000 0000

ADDL

0000 0000

CCAP2L

0000 0000

CCAPM2

x000 0000

SPCON

0001 0100

TL2

0000 0000

CCAP3H

0000 0000

ADDH

0000 0000

CCAP3L

0000 0000

CCAPM3

x000 0000

SPSCR

0000 0000

TH2

0000 0000

CCAP4H

0000 0000

ADCF

0000 0000

CCAP4L

0000 0000

CCAPM4

x000 0000

SPDAT

xxxx xxxx

IPH1

xxxx x0x0

IPH0

x000 0000

FFh

F7h

EFh

E7h

DFh

D7h

CFh

C7h

BFh

B7h

AFh

A0h

98h

90h

88h

80h

1111 1111

SCON

0000 0000

1111 1111

TCON

0000 0000

1111 1111

(2)

0/8

SBUF

0000 0000

TMOD

0000 0000

0000 0111

1/9 2/A 3/B 4/C 5/D 6/E 7/F

AUXR1

xxxx 00x0

TL0

0000 0000

DPL

0000 0000

Reserved

Note: 1. Do not read or write Reserved Registers

2. These registers are bit–addressable. Sixteen addresses in the SFR space are both byte–addressable and bit–addressable. The bit–addressable SFR’s are those whose address ends in 0 and 8. The bit addresses, in this area, are 0x80 through to 0xFF.

TL1

0000 0000

DPH

0000 0000

TH0

0000 0000

TH1

0000 0000

WDTRST 1111 1111

AUXR

x001 0100

WDTPRG xxxx x000

CKCON1

xxxx xxx0

CKCON0 x00 0000

PCON

00x1 0000

A7h

9Fh

97h

8Fh

87h

4383D–8051–02/08

AT89C51AC3

Clock

Description

The AT89C51AC3 core needs only 6 clock periods per machine cycle. This feature, called”X2”, provides the following advantages:

• Divides frequency crystals by 2 (cheaper crystals) while keeping the same CPU power.

• Saves power consumption while keeping the same CPU power (oscillator power saving).

• Saves power consumption by dividing dynamic operating frequency by 2 in operating and idle modes.

• Increases CPU power by 2 while keeping the same crystal frequency.

In order to keep the original C51 compatibility, a divider-by-2 is inserted between the XTAL1 signal and the main clock input of the core (phase generator). This divider may be disabled by the software.

An extra feature is available to start after Reset in the X2 mode. This feature can be enabled by a bit X2B in the Hardware Security Byte. This bit is described in the section "In-System Programming".

The X2 bit in the CKCON register (see Table 2) allows switching from 12 clock cycles per instruction to 6 clock cycles and vice versa. At reset, the standard speed is activated (STD mode).

Setting this bit activates the X2 feature (X2 mode) for the CPU Clock only (see Figure

5.).

The Timers 0, 1 and 2, Uart, PCA or WatchDog switch in X2 mode only if the corresponding bit is cleared in the CKCON register.

The clock for the whole circuit and peripheral is first divided by two before being used by the CPU core and peripherals. This allows any cyclic ratio to be accepted on the XTAL1 input. In X2 mode, as this divider is bypassed, the signals on XTAL1 must have a cyclic ratio between 40 to 60%. Figure 5. shows the clock generation block diagram. The X2 bit is validated on the XTAL1÷2 rising edge to avoid glitches when switching from the X2 to the STD mode. Figure 6 shows the mode switching waveforms.

4383D–8051–02/08

AT89C51AC3

Figure 5. Clock CPU Generation Diagram

XTAL1

XTAL2

PCON.1

CPU Core

PERIPH

CLOCK

Clock

Peripheral

CPU

CLOCK

CPU Core Clock Symbol

CKCON.0

X2B

Hardware byte

WDX2

CKCON0.6

PCAX2

CKCON0.5

SIX2

CKCON0.4

T2X2

CKCON0.3

T1X2

CKCON0.2

T0X2

CKCON0.1

IDL

PCON.0

CKCON.0

FWd Clock

FPca Clock

FUart Clock

FT2 Clock

FT1 Clock

FT0 Clock

and ADC

On RESET

FSPIClock

SPIX2

CKCON1.0

Clock Symbol

4383D–8051–02/08

AT89C51AC3

XTAL1/2

XTAL1

CPU clock

X2 bit

X2 ModeSTD Mode STD Mode

Figure 6. Mode Switching Waveforms

Note: In order to prevent any incorrect operation while operating in the X2 mode, users must be aware that all peripherals using the

clock frequency as a time reference (UART, timers...) will have their time reference divided by two. For example a free running timer generating an interrupt every 20 ms will then generate an interrupt every 10 ms. A UART with a 4800 baud rate will have a 9600 baud rate.

4383D–8051–02/08

AT89C51AC3

Registers

Table 2. CKCON0 Register

CKCON0 (S:8Fh) Clock Control Register

7 6 5 4 3 2 1 0

- WDX2 PCAX2 SIX2 T2X2 T1X2 T0X2 X2

Bit

Number

7 -

6 WDX2

5 PCAX2

4 SIX2

3 T2X2

2 T1X2

1 T0X2

0 X2

Bit

Mnemonic Description

Reserved

The value read from this bits is indeterminate. Do not set this bit.

WatchDog clock

Clear to select 6 clock periods per peripheral clock cycle. Set to select 12 clock periods per peripheral clock cycle.

Programmable Counter Array clock

Clear to select 6 clock periods per peripheral clock cycle. Set to select 12 clock periods per peripheral clock cycle.

Enhanced UART clock (MODE 0 and 2)

Clear to select 6 clock periods per peripheral clock cycle. Set to select 12 clock periods per peripheral clock cycle.

Timer2 clock

Clear to select 6 clock periods per peripheral clock cycle. Set to select 12 clock periods per peripheral clock cycle.

Timer1 clock

Clear to select 6 clock periods per peripheral clock cycle. Set to select 12 clock periods per peripheral clock cycle.

Timer0 clock

Clear to select 6 clock periods per peripheral clock cycle. Set to select 12 clock periods per peripheral clock cycle.

CPU clock

Clear to select 12 clock periods per machine cycle (STD mode) for CPU and all the peripherals. Set to select 6 clock periods per machine cycle (X2 mode) and to enable the individual peripherals "X2"bits.

(1)

Note: 1. This control bit is validated when the CPU clock bit X2 is set; when X2 is low, this bit

has no effect.

Reset Value = x000 0000b

4383D–8051–02/08

AT89C51AC3

Table 3. CKCON1 Register

CKCON1 (S:9Fh) Clock Control Register 1

7 6 5 4 3 2 1 0

SPIX2

Bit

Number

7-1 -

0 SPIX2

Bit

Mnemonic Description

Reserved

The value read from these bits is indeterminate. Do not set these bits.

SPI clock

Clear to select 6 clock periods per peripheral clock cycle. Set to select 12 clock periods per peripheral clock cycle.

(1)

Note: 1. This control bit is validated when the CPU clock bit X2 is set; when X2 is low, this bit

has no effect.

Reset Value = XXXX XXX0b

4383D–8051–02/08

AT89C51AC3

Data Memory

Upper

128 Bytes

Internal RAM

Lower

128 Bytes

Internal RAM

Special

Function

Registers

80h

00h

FFh

direct addressing

addressing

7Fh

direct or indirect

indirect addressing

256 up to 2048 Bytes

00h

64K Bytes

External XRAM

0000h

FFFFh

Internal ERAM

EXTRAM = 0

EXTRAM = 1

FFh or 7FFh

Internal

External

The AT89C51AC3 provides data memory access in two different spaces:

1. The internal space mapped in three separate segments:

• the lower 128 Bytes RAM segment.

• the upper 128 Bytes RAM segment.

• the expanded 2048 Bytes RAM segment (ERAM).

2. The external space.

A fourth internal segment is available but dedicated to Special Function Registers, SFRs, (addresses 80h to

FFh

) accessible by direct addressing mode.

Figure 8 shows the internal and external data memory spaces organization.

Figure 7. Internal Memory - RAM

Figure 8. Internal and External Data Memory Organization ERAM-XRAM

4383D–8051–02/08

AT89C51AC3

Bit-Addressable Space

4 Banks of 8 Registers R0-R7

30h

7Fh

(Bit Addresses 0-7Fh)

20h

2Fh

18h

1Fh

10h

17h

08h

0Fh

00h

07h

Internal Space

Lower 128 Bytes RAM The lower 128 Bytes of RAM (see Figure 8) are accessible from address 00h to 7Fh

using direct or indirect addressing modes. The lowest 32 Bytes are grouped into 4 banks of 8 registers (R0 to R7). Two bits RS0 and RS1 in PSW register (see Figure 6) select which bank is in use according to Table 4. This allows more efficient use of code space, since register instructions are shorter than instructions that use direct addressing, and can be used for context switching in interrupt service routines.

Table 4. Register Bank Selection

RS1 RS0 Description

0 0 Register bank 0 from 00h to 07h

0 1 Register bank 0 from 08h to 0Fh

1 0 Register bank 0 from 10h to 17h

1 1 Register bank 0 from 18h to 1Fh

The next 16 Bytes above the register banks form a block of bit-addressable memory space. The C51 instruction set includes a wide selection of single-bit instructions, and the 128 bits in this area can be directly addressed by these instructions. The bit addresses in this area are 00h to 7Fh.

Figure 9. Lower 128 Bytes Internal RAM Organization

Upper 128 Bytes RAM The upper 128 Bytes of RAM are accessible from address 80h to FFh using only indirect

addressing mode.

Expanded RAM The on-chip 2048 Bytes of expanded RAM (ERAM) are accessible from address 0000h

to 07FFh using indirect addressing mode through MOVX instructions. In this address range, the bit EXTRAM in AUXR register is used to select the ERAM (default) or the XRAM. As shown in Figure 8 when EXTRAM = 0, the ERAM is selected and when EXTRAM = 1, the XRAM is selected.

The size of ERAM can be configured by XRS2-0 bit in AUXR register (default size is 2048 Bytes).

4383D–8051–02/08

Note: Lower 128 Bytes RAM, Upper 128 Bytes RAM, and expanded RAM are made of volatile

memory cells. This means that the RAM content is indeterminate after power-up and must then be initialized properly.

AT89C51AC3

External Space

RAM

PERIPHERAL

AT89C51AC3

AD7:0

A15:8

A7:0

A15:8

D7:0

A7:0

ALE

OERD#

WR#

Latch

Memory Interface The external memory interface comprises the external bus (port 0 and port 2) as well as

the bus control signals (RD#, WR#, and ALE).

Figure 10 shows the structure of the external address bus. P0 carries address A7:0 while P2 carries address A15:8. Data D7:0 is multiplexed with A7:0 on P0. Table 5 describes the external memory interface signals.

Figure 10. External Data Memory Interface Structure

Table 5. External Data Memory Interface Signals

Signal

Name Type Description

A15:8 O

AD7:0 I/O

ALE O

RD# O

WR# O

Address Lines

Upper address lines for the external bus.

Address/Data Lines

Multiplexed lower address lines and data for the external memory.

Address Latch Enable

ALE signals indicates that valid address information are available on lines AD7:0.

Read

Read signal output to external data memory.

Write

Write signal output to external memory.

Alternative

Function

P2.7:0

P0.7:0

P3.7

P3.6

External Bus Cycles This section describes the b us cycles the AT89C51AC3 execu tes to read (see

Figure 11), and write data (see Figure 12) in the external data memory. External memory cycle takes 6 CPU clock periods. This is equivalent to 12 oscillator clock period in standard mode or 6 oscillator clock periods in X2 mode. For further information on X2 mode.

Slow peripherals can be accessed by stretching the read and write cycles. This is done using the M0 bit in AUXR register. Setting this bit changes the width of the RD# and WR# signals from 3 to 15 CPU clock periods.

For simplicity, the accompanying figures depict the bus cycle waveforms in idealized form and do not provide precise timing information. For bus cycle timing parameters refer to the Section “AC Characteristics” of the AT89C51AC3 datasheet.

4383D–8051–02/08

AT89C51AC3

ALE

RD#1

DPL or Ri D7:0

DPH or P22

CPU Clock

ALE

WR#1

DPL or Ri D7:0

CPU Clock

DPH or P22

Figure 11. External Data Read Waveforms

Notes: 1. RD# signal may be stretched using M0 bit in AUXR register.

2. When executing MOVX @Ri instruction, P2 outputs SFR content.

Figure 12. External Data Write Waveforms

4383D–8051–02/08

Notes: 1. WR# signal may be stretched using M0 bit in AUXR register.

2. When executing MOVX @Ri instruction, P2 outputs SFR content.

AT89C51AC3

Dual Data Pointer

DPH0

DPH1

DPL0

DPS

AUXR1.0

DPH

DPL

DPL1

DPTR

DPTR0

DPTR1

Description The AT89C51AC3 implements a second data pointer for speeding up code execution

and reducing code size in case of intensive usage of external memory accesses. DPTR 0 and DPTR 1 are seen by the CPU as DPTR and are accessed using the SFR addresses 83h and 84h that are the DPH and DPL addresses. The DPS bit in AUXR1 register (see Figure 8) is used to select whether DPTR is the data pointer 0 or the data pointer 1 (see Figure 13).

Figure 13. Dual Data Pointer Implementation

Application Software can take advantage of the additional data pointers to both increase speed and

reduce code size, for example, block operations (copy, compare…) are well served by using one data pointer as a “source” pointer and the other one as a “destination” pointer. Hereafter is an example of block move implementation using the two pointers and coded in assembler. The latest C compiler takes also advantage of this feature by providing enhanced algorithm libraries.

The INC instruction is a short (2 Bytes) and fast (6 machine cycle) way to manipulate the DPS bit in the AUXR1 register. However, note that the INC instruction does not directly force the DPS bit to a particular state, but simply toggles it. In simple routines, such as the block move example, only the fact that DPS is toggled in the proper sequence matters, not its actual value. In other words, the block move routine works the same whether DPS is '0' or '1' on entry.

; ASCII block move using dual data pointers ; Modifies DPTR0, DPTR1, A and PSW ; Ends when encountering NULL character ; Note: DPS exits opposite to the entry state unless an extra INC AUXR1 is added

AUXR1EQU0A2h

move:movDPTR,#SOURCE ; address of SOURCE

incAUXR1 ; switch data pointers movDPTR,#DEST ; address of DEST

mv_loop:incAUXR1; switch data pointers

movxA,@DPTR; get a byte from SOURCE incDPTR; increment SOURCE address incAUXR1; switch data pointers movx@DPTR,A; write the byte to DEST incDPTR; increment DEST address jnzmv_loop; check for NULL terminator

end_move:

4383D–8051–02/08

AT89C51AC3

Registers

Table 6. PSW Register

PSW (S:8Eh) Program Status Word Register

7 6 5 4 3 2 1 0

CY AC F0 RS1 RS0 OV F1 P

Bit

Number

7 CY

6 AC

5 F0

4-3 RS1:0

2 OV

1 F1

0 P

Bit

Mnemonic Description

Carry Flag

Carry out from bit 1 of ALU operands.

Auxiliary Carry Flag

Carry out from bit 1 of addition operands.

User Definable Flag 0.

Refer to Table 4 for bits description.

Overflow Flag

Overflow set by arithmetic operations.

User Definable Flag 1

Parity Bit

Set when ACC contains an odd number of 1’s. Cleared when ACC contains an even number of 1’s.

Reset Value = 0000 0000b

Table 7. AUXR Register

AUXR (S:8Eh) Auxiliary Register

7 6 5 4 3 2 1 0

- - M0 XRS2 XRS1 XRS0 EXTRAM A0

Bit

Number

7-6 -

5 M0

Bit

Mnemonic Description

Reserved

The value read from these bits are indeterminate. Do not set this bit.

Stretch MOVX control:

the RD/ and the WR/ pulse length is increased according to the value of M0.

M0 Pulse length in clock period

0 6 1 30

4383D–8051–02/08

AT89C51AC3

Bit

Number

4-2 XRS1-0

1 EXTRAM

0 A0

Bit

Mnemonic Description

ERAM size:

Accessible size of the ERAM

XRS 2:0 ERAM size

000 256 Bytes 001 512 Bytes 010 768 Bytes 011 1024 Bytes

100 1792 Bytes

101 2048 Bytes (default configuration after reset)

110 Reserved

111 Reserved

Internal/External RAM (00h - FFh)

access using MOVX @ Ri/@ DPTR 0 - Internal ERAM access using MOVX @ Ri/@ DPTR. 1 - External data memory access.

Disable/Enable ALE)

0 - ALE is emitted at a constant rate of 1/6 the oscillator frequency (or 1/3 if X2 mode is used) 1 - ALE is active only during a MOVX or MOVC instruction.

Reset Value = X001 0100b Not bit addressable

Table 8. AUXR1 Register

AUXR1 (S:A2h) Auxiliary Control Register 1

7 6 5 4 3 2 1 0

- - ENBOOT - GF3 0 - DPS

Bit

Number

7-6 -

5 ENBOOT

4 -

3 GF3

2 0

1 -

0 DPS

Bit

Mnemonic Description

Reserved

The value read from these bits is indeterminate. Do not set these bits.

Enable Boot Flash

Set this bit for map the boot Flash between F800h -FFFFh Clear this bit for disable boot Flash.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

General-purpose Flag 3

Always Zero

This bit is stuck to logic 0 to allow INC AUXR1 instruction without affecting GF3 flag.

Reserved for Data Pointer Extension.

Data Pointer Select Bit

Set to select second dual data pointer: DPTR1. Clear to select first dual data pointer: DPTR0.

Reset Value = XXXX 00X0b

4383D–8051–02/08

AT89C51AC3

VCC

Power On Reset Power Fail Detect Voltage Regulator

XTAL1

(1)

CPU core

Memories

Peripherals

Regulated Supply

RST pin

Hardware Watchdog

PCA Watchdog

Internal Reset

Power Monitor

The POR/PFD function monitors the internal power-supply of the CPU core memories and the peripherals, and if needed, suspends their activity when the internal power supply falls below a safety threshold. This is achieved by applying an internal reset to them.

By g enera ting t he Res et the Power Monit or in sures a corr ect st art up w hen AT89C51CC03 is powered up.

Description

In order to startup and maintain the microcontroller in correct operating mode, VCC has to be stabilized in the VCC operating range and the oscillator has to be stabilized with a nominal amplitude compatible with logic level VIH/VIL.

These parameters are controlled during the three phases: power-up, normal operation and power going down. See Figure 14.

Figure 14. Power Monitor Block Diagram

Note: 1. Once XTAL1 high and low levels reach above and below VIH/VIL a 1024 clock period

delay will extend the reset coming from the Power Fail Detect. If the power falls below the Power Fail Detect thresthold level, the reset will be applied immediately.

The Voltage regulator generates a regulated internal supply for the CPU core the memories and the peripherals. Spikes on the external Vcc are smoothed by the voltage regulator.

The Power fail detect monitor the supply generated by the voltage regulator and generate a reset if this supply falls below a safety threshold as illustrated in the Figure 15.

4383D–8051–02/08

AT89C51AC3

Figure 15. Power Fail Detect

Vcc

Reset

Vcc

When the power is applied, the Power Monitor immediately asserts a reset. Once the internal supply after the voltage regulator reach a safety level, the power monitor then looks at the XTAL clock input. The internal reset will remain asserted until the Xtal1 levels are above and below VIH and VIL. Further more. An internal counter will count 1024 clock periods before the reset is de-asserted.

If the internal power supply falls below a safety level, a reset is immediately asserted.

4383D–8051–02/08

Reset

Power

Monitor

Hardware Watchdog

PCA

Watchdog

RST

Internal Reset

RST

VSS

To internal reset

RST

VDD

b. Power-on Reseta. RST input circuitry

AT89C51AC3

Introduction

Reset Input

The reset sources are : Power Management, Hardware Watchdog, PCA Watchdog and Reset input.

Figure 16. Reset Schematic

The Reset input can be used to force a reset pulse longer than the internal reset controlled by the Power Monitor. RST input has a pull-down resistor allowing power-on reset by simply connecting an external capacitor to VCC as shown in Figure 17. Resistor value and input characteristics are discussed in the Section “DC Characteristics” of the AT89C51AC3 datasheet. The status of the Port pins during reset is detailed in Table 9.

4383D–8051–02/08

Figure 17. Reset Circuitry and Power-On Reset

AT89C51AC3

Reset Output

RST

VDD

VSS

VDD

RST

To other on-board

circuitry

AT89C51AC3

As detailed in Section “Watchdog Timer”, page 79, the WDT generates a 96-clock period pulse on the RST pin. In order to properly propagate this pulse to the rest of the application in case of external capacitor or power-supply supervisor circuit, a 1 kΩ resistor must be added as shown Figure 18.

Figure 18. Recommended Reset Output Schematic

4383D–8051–02/08

Power Management

AT89C51AC3

Introduction

Two power reduction modes are implemented in the AT89C51AC3. The Idle mode and the Power-Down mode. These modes are detailed in the following sections. In addition to these power reduction modes, the clocks of the core and peripherals can be dynamically divided by 2 using the X2 mode detailed in Section “Clock”, page 15.

Idle Mode

Idle mode is a power reduction mode that reduces the power consumption. In this mode, program execution halts. Idle mode freezes the clock to the CPU at known states while the peripherals continue to be clocked. The CPU status before entering Idle mode is preserved, i.e., the program counter and program status word register retain their data for the duration of Idle mode. The contents of the

SFRs

and RAM are also retained. The

status of the Port pins during Idle mode is detailed in Table 9.

Entering Idle Mode To enter Idle mode, set the IDL bit in PCON register (see Table 10). The AT89C51AC3

enters Idle mode upon execution of the instruction that sets IDL bit. The instruction that sets IDL bit is the last instruction executed.

Note: If IDL bit and PD bit are set simultaneously, the AT89C51AC3 enters Power-Down mode.

Then it does not go in Idle mode when exiting Power-Down mode.

Exiting Idle Mode There are two ways to exit Idle mode:

1. Generate an enabled interrupt.

– Hardware clears IDL bit in PCON register which restores the clock to the

CPU. Execution resumes with the interrupt service routine. Upon completion of the interrupt service routine, program execution resumes with the instruction immediately following the instruction that activated Idle mode. The general purpose flags (GF1 and GF0 in PCON register) may be used to indicate whether an interrupt occurred during normal operation or during Idle mode. When Idle mode is exited by an interrupt, the interrupt service routine may examine GF1 and GF0.

2. Generate a reset.

– A logic high on the RST pin clears IDL bit in PCON register directly and

asynchronously. This restores the clock to the CPU. Program execution momentarily resumes with the instruction immediately following the instruction that activated the Idle mode and may continue for a number of clock cycles before the internal reset algorithm takes control. Reset initializes the AT89C51AC3 and vectors the CPU to address C:0000h.

Power-Down Mode

4383D–8051–02/08

Note: During the time that execution resumes, the internal RAM cannot be accessed; however,

it is possible for the Port pins to be accessed. To avoid unexpected outputs at the Port pins, the instruction immediately following the instruction that activated Idle mode should not write to a Port pin or to the external RAM.

The Power-Down mode places the AT89C51AC3 in a very low power state. PowerDown mode stops the oscillator, freezes all clock at known states. The CPU status prior to entering Power-Down mode is preserved, i.e., the program counter, program status word register retain their data for the duration of Power-Down mode. In addition, the

SFR

and RAM contents are preserved. The status of the Port pins during Power-Down mode is detailed in Table 9.

Note: VCC may be reduced to as low as V

power dissipation. Take care, however, that VDD is not reduced until Power-Down mode is invoked.

during Power-Down mode to further reduce

RET

AT89C51AC3

Entering Power-Down Mode To enter Power-Down mode, set PD bit in PCON register. The AT89C51AC3 enters the

INT1:0#

OSC

Power-down phase Oscillator restart phase Active phaseActive phase

Power-Down mode upon execution of the instruction that sets PD bit. The instruction that sets PD bit is the last instruction executed.

Exiting Power-Down Mode

Note: If VCC was reduced during the Power-Down mode, do not exit Power-Down mode until

VCC is restored to the normal operating level.

There are two ways to exit the Power-Down mode:

1. Generate an enabled external interrupt.

– The AT89C51AC3 provides capability to exit from Power-Down using INT0#,

INT1#. Hardware clears PD bit in PCON register which starts the oscillator and restores the clocks to the CPU and peripherals. Using INTx# input, execution resumes when the input is released (see Figure 19). Execution resumes with the interrupt service routine. Upon completion of the interrupt service routine, program execution resumes with the instruction immediately following the instruction that activated Power-Down mode.

Note: The external interrupt used to exit Power-Down mode must be configured as level sensi-

tive (INT0# and INT1#) and must be assigned the highest priority. In addition, the duration of the interrupt must be long enough to allow the oscillator to stabilize. The execution will only resume when the interrupt is deasserted.

Note: Exit from power-down by external interrupt does not affect the

content.

SFRs

nor the internal RAM

Figure 19. Power-Down Exit Waveform Using INT1:0#

2. Generate a reset.

– A logic high on the RST pin clears PD bit in PCON register directly and

asynchronously. This starts the oscillator and restores the clock to the CPU and peripherals. Program execution momentarily resumes with the instruction immediately following the instruction that activated Power-Down mode and may continue for a number of clock cycles before the internal reset algorithm takes control. Reset initializes the AT89C51AC3 and vectors the CPU to address 0000h.

Note: During the time that execution resumes, the internal RAM cannot be accessed; however,

it is possible for the Port pins to be accessed. To avoid unexpected outputs at the Port pins, the instruction immediately following the instruction that activated the Power-Down mode should not write to a Port pin or to the external RAM.

Note: Exit from power-down by reset redefines all the

RAM content.

SFRs

, but does not affect the internal

4383D–8051–02/08

AT89C51AC3

Table 9. Pin Conditions in Special Operating Modes

Mode Port 0 Port 1 Port 2 Port 3 Port 4 ALE PSEN#

Reset Floating High High High High High High

Idle

(internal

code)

Idle

(external

code)

Power-

Down(inter

nal code)

Power-

Down

(external

code)

Data Data Data Data Data High High

Floating Data Data Data Data High High

Data Data Data Data Data Low Low

Floating Data Data Data Data Low Low

4383D–8051–02/08

AT89C51AC3

Registers

Table 10. PCON Register

PCON (S87:h) Power configuration Register

7 6 5 4 3 2 1 0

- - - - GF1 GF0 PD IDL

Bit

Number

7-4 -

3 GF1

2 GF0

1 PD

0 IDL

Bit

Mnemonic Description

Reserved

The value read from these bits is indeterminate. Do not set these bits.

General Purpose flag 1

One use is to indicate whether an interrupt occurred during normal operation or during Idle mode.

General Purpose flag 0

One use is to indicate whether an interrupt occurred during normal operation or during Idle mode.

Power-Down Mode bit

Cleared by hardware when an interrupt or reset occurs. Set to activate the Power-Down mode. If IDL and PD are both set, PD takes precedence.

Idle Mode bit

Cleared by hardware when an interrupt or reset occurs. Set to activate the Idle mode. If IDL and PD are both set, PD takes precedence.

Reset Value= XXXX 0000b

4383D–8051–02/08

AT89C51AC3

EEPROM Data Memory

Write Data in the Column Latches

The 2-Kbyte on-chip EEPROM memory block is located at addresses 0000h to 07FFh of the XRAM/ERAM memory space and is selected by setting control bits in the EECON register. A read in the EEPROM memory is done with a MOVX instruction.

A physical write in the EEPROM memory is done in two steps: write data in the column latches and transfer of all data latches into an EEPROM memory row (programming).

The number of data written on the page may vary from 1 up to 128 Bytes (the page size). When programming, only the data written in the column latch is programmed and a ninth bit is used to obtain this feature. This provides the capability to program the whole memory by Bytes, by page or by a number of Bytes in a page. Indeed, each ninth bit is set when the writing the corresponding byte in a row and all these ninth bits are reset after the writing of the complete EEPROM row.

Data is written by byte to the column latches as for an external RAM memory. Out of the 11 address bits of the data pointer, the 4 MSBs are used for page selection (row) and 7 are used for byte selection. Between two EEPROM programming sessions, all the addresses in the column latches must stay on the same page, meaning that the 4 MSB must no be changed.

The following procedure is used to write to the column latches:

• Save and disable interrupt.

• Set bit EEE of EECON register

• Load DPTR with the address to write

• Store A register with the data to be written

• Execute a MOVX @DPTR, A

• If needed loop the three last instructions until the end of a 128 Bytes page

• Restore interrupt.

Note: The last page address used when loading the column latch is the one used to select the

page programming address.

Programming

Read Data

4383D–8051–02/08

The EEPROM programming consists of the following actions:

• writing one or more Bytes of one page in the column latches. Normally, all Bytes must belong to the same page; if not, the first page address will be latched and the others discarded.

• launching programming by writing the control sequence (50h followed by A0h) to the EECON register.

• EEBUSY flag in EECON is then set by hardware to indicate that programming is in progress and that the EEPROM segment is not available for reading.

• The end of programming is indicated by a hardware clear of the EEBUSY flag.

Note: The sequence 5xh and Axh must be executed without instructions between then other-

wise the programming is aborted.

The following procedure is used to read the data stored in the EEPROM memory:

• Save and disable interrupt

• Set bit EEE of EECON register

• Load DPTR with the address to read

• Execute a MOVX A, @DPTR

• Restore interrupt

AT89C51AC3

Examples

;*F*************************************************************************;* NAME: api_rd_eeprom_byte

;* DPTR contain address to read.

;* Acc contain the reading value

;* NOTE: before execute this function, be sure the EEPROM is not BUSY

;***************************************************************************

api_rd_eeprom_byte:

MOV EECON, #02h; map EEPROM in XRAM space

MOVX A, @DPTR

MOV EECON, #00h; unmap EEPROM

ret

;*F*************************************************************************

;* NAME: api_ld_eeprom_cl

;* DPTR contain address to load

;* Acc contain value to load

;* NOTE: in this example we load only 1 byte, but it is possible upto

;* 128 Bytes.

;* before execute this function, be sure the EEPROM is not BUSY

;***************************************************************************

api_ld_eeprom_cl:

MOV EECON, #02h ; map EEPROM in XRAM space

MOVX @DPTR, A

MOVEECON, #00h; unmap EEPROM

ret

;*F*************************************************************************

;* NAME: api_wr_eeprom

;* NOTE: before execute this function, be sure the EEPROM is not BUSY

;***************************************************************************

api_wr_eeprom:

MOV EECON, #050h

MOV EECON, #0A0h

ret

4383D–8051–02/08

AT89C51AC3

Registers

Table 11. EECON Register

EECON (S:0D2h) EEPROM Control Register

7 6 5 4 3 2 1 0

EEPL3 EEPL2 EEPL1 EEPL0 - - EEE EEBUSY

Bit

Bit Number

7-4 EEPL3-0

3 -

2 -

1 EEE

0 EEBUSY

Mnemonic Description

Programming Launch command bits

Write 5Xh followed by AXh to EEPL to launch the programming.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Enable EEPROM Space bit

Set to map the EEPROM space during MOVX instructions (Write in the column latches) Clear to map the XRAM space during MOVX.

Programming Busy flag

Set by hardware when programming is in progress. Cleared by hardware when programming is done. Can not be set or cleared by software.

Reset Value = XXXX XX00b Not bit addressable

4383D–8051–02/08

AT89C51AC3

Program/Code

0000h

64K Bytes

FFFFh

internal

0000h

FFFFh

Flash

64K Bytes

external memory

EA = 0

EA = 1

Memory

The AT89C51AC3 implement 64K Bytes of on-chip program/code memory. Figure 20 shows the partitioning of internal and external program/code memory spaces depending on the product.

The Flash memory increases EPROM and ROM functionality by in-circuit electrical erasure and programming. Thanks to the internal charge pump, the high voltage needed for programming or erasing Flash cells is generated on-chip using the standard VDD voltage. Thus, the Flash Memory can be programmed using only one voltage and allows InSystem Programming commonly known as ISP. Hardware programming mode is also available using specific programming tool.

Figure 20. Program/Code Memory Organization

4383D–8051–02/08

AT89C51AC3

Flash

EPROM

AT89C51AC3

AD7:0

A15:8

A7:0

A15:8

D7:0

A7:0

ALE

Latch

OEPSEN#

External Code Memory Access

Memory Interface The external memory interface comprises the external bus (port 0 and port 2) as well as

the bus control signals (PSEN#, and ALE).

Figure 21 shows the structure of the external address bus. P0 carries address A7:0 while P2 carries address A15:8. Data D7:0 is multiplexed with A7:0 on P0. Table 21 describes the external memory interface signals.

Figure 21. External Code Memory Interface Structure

Table 12. External Code Memory Interface Signals

Signal

Name Type Description

A15:8 O

AD7:0 I/O

ALE O

PSEN# O

Address Lines

Upper address lines for the external bus.

Address/Data Lines

Multiplexed lower address lines and data for the external memory.

Address Latch Enable

ALE signals indicates that valid address information are available on lines AD7:0.

Program Store Enable Output

This signal is active low during external code fetch or external code read (MOVC instruction).

Alternate Function

P2.7:0

P0.7:0

External Bus Cycles This section describes the bus cycles the AT89C51AC3 executes to fetch code (see

Figure 22) in the external program/code memory.

External memory cycle takes 6 CPU clock periods. This is equivalent to 12 oscillator clock period in standard mode or 6 oscillator clock periods in X2 mode. For further information on X2 mode see section “Clock “.

For simplicity, the accompanying figure depicts the bus cycle waveforms in idealized form and do not provide precise timing information.

For bus cycling parameters refer to the ‘AC-DC parameters’ section.

4383D–8051–02/08

AT89C51AC3

Figure 22. External Code Fetch Waveforms

ALE

PSEN#

PCL

PCHPCH

PCLD7:0 D7:0

PCH

D7:0

CPU Clock

FFFFh

64K Bytes

FM0

0000h

Hardware Security (1 byte)

Column Latches (128 Bytes)

Extra Row (128 Bytes)

2K Bytes

Flash memory

FM1

boot space

FFFFh

F800h

FM1 mapped between FFFFh and F800h when bit ENBOOT is set in AUXR1 register

F800h

Memory space not accessible

Flash Memory Architecture

AT89C51AC3 features two on-chip Flash memories:

• Flash memory FM0: containing 64K Bytes of program memory (user space) organized into 128 byte pages,

• Flash memory FM1: 2K Bytes for boot loader and Application Programming Interfaces (API).

The FM0 can be program by both parallel programming and Serial In-System Programming (ISP) whereas FM1 supports only parallel programming by programmers. The ISP mode is detailed in the "In-System Programming" section.

All Read/Write access operations on Flash Memory by user application are managed by a set of API described in the "In-System Programming" section.

The bit ENBOOT in AUXR1 register is used to map FM1 from F800h to FFFFh. Figure 23 and Fi gur e 24 show the Flash m emory configuration w ith ENBOOT=1 and ENBOOT=0.

Figure 23. Flash Memory Architecture with ENBOOT=1 (boot mode)

4383D–8051–02/08

Figure 24. Flash Memory Architecture with ENBOOT=0 (user modemode)

FFFFh

64K Bytes

FM0

0000h

Hardware Security (1 byte)

Column Latches (128 Bytes)

Extra Row (128 Bytes)

2K Bytes

Flash memory

FM1

boot space

FFFFh

F800h

FM1 mapped between FFFFh and F800h when bit ENBOOT is set in AUXR1 register

F800h

Memory space not accessible

AT89C51AC3

4383D–8051–02/08

AT89C51AC3

FM0 Memory Architecture The Flash memory is made up of 4 blocks (see Figure 23):

• The memory array (user space) 64K Bytes

• The Extra Row

• The Hardware security bits

• The column latch registers

User Space This space is composed of a 64K Bytes Flash memory organized in 512 pages of 128

Bytes. It contains the user’s application code.

Extra Row (XRow) This row is a part of FM0 and has a size of 128 Bytes. The extra row may contain infor-

mation for boot loader usage.

Hardware security Byte (HSB) The Hardware security Byte space is a part of FM0 and has a size of 1 byte.

The 4 MSB can be read/written by software (from FM0 and , the 4 LSB can only be read by software and written by hardware in parallel mode.

H Hardware Security Byte (HSB)

7 6 5 4 3 2 1 0

X2 BLJB - - - LB2 LB1 LB0

Bit

Number

7 X2

6 BLJB

5 -

4 -

3 -

2-0 LB2-0

Bit

Mnemonic Description

X2 Mode

Programmed (=’0’) to force X2 mode (6 clocks per instruction) after reset

Unprogrammed to force X1 mode, Standard Mode, afetr reset (Default)

Boot Loader Jump Bit

When unprogrammed (=’1’), at the next reset :

-ENBOOT=0 (see code space memory configuration)

-Start address is 0000h (PC=0000h)

When programmed (=’0’)at the nex reset:

-ENBOOT=1 (see code space memory configuration)

-Start address is F800h (PC=F800h)

Reserved

General Memory Lock Bits (only programmable by programmer tools)

Section “Flash Protection from Parallel Programming”, page 51

Column Latches The column latches, also part of FM0, have a size of full page (128 Bytes).

The column latches are the entrance buffers of the three previous memory locations (user array, XROW and Hardware security byte). The column latches are write only and can be accessed only from FM1 (boot mode) and from external memory

Cross Flash Memory Access Description

The FM0 memory can be program only from FM1. Programming FM0 from FM0 or from external memory is impossible.

The FM1 memory can be program only by parallel programming.

The Table show all software Flash access allowed.

4383D–8051–02/08

Cross Flash Memory Access

AT89C51AC3

Action

Read ok -

Load column latch ok -

Write - -

Read ok ok

Load column latch ok -

Write ok -

Read (a) -

Load column latch - -

Write - -

(user Flash)

(boot Flash)

Code executing from

FM0

FM1

External

memory

EA = 0

(a) Depend upon general lock bit configuration.

FM0

(user Flash)

FM1

(boot Flash)

4383D–8051–02/08

AT89C51AC3

Overview of FM0 Operations

Flash Registers (SFR)

FCON Register

The CPU interfaces to the flash memory through the FCON register, AUXR1 register and FSTA register.

These registers are used to map the column latches, HSB, extra row and EEDATA in the working data or code space.

Table 13. FCON Register

FCON Register (S:D1h) Flash Control Register

7 6 5 4 3 2 1 0

FPL3 FPL2 FPL1 FPL0 FPS FMOD1 FMOD0 FBUSY

Bit

Number

7-4 FPL3:0

3 FPS

2-1 FMOD1:0

0 FBUSY

Bit

Mnemonic Description

Programming Launch Command Bits

Write 5Xh followed by AXh to launch the programming according to FMOD1:0. (see Table 16.)

Flash Map Program Space

When this bit is set:

The MOVX @DPTR, A instruction writes in the columns latches space

When this bit is cleared:

The MOVX @DPTR, A instruction writes in the regular XDATA memory space

Flash Mode

See Table 16.

Flash Busy

Set by hardware when programming is in progress. Clear by hardware when programming is done. Can not be changed by software.

Reset Value= 0000 0000b

4383D–8051–02/08

FSTA Register

AT89C51AC3

Table 14. FSTA Register

FSTA Register (S:D3h) Flash Status Register

7 6 5 4 3 2 1 0

SEQERR FLOAD

Bit

Number

7-2

1 SEQERR

0 FLOAD

Bit

Mnemonic Description

unusesd

Flash activation sequence error

Set by hardware when the flash activation sequence(MOV FCON 5X and MOV FCON AX )is not correct (See Error Repport Section)

Clear by software or clear by hardware if the last activation sequence was correct (previous error are canceled)

Flash Colums latch loaded

Set by hardware when the first data is loaded in the column latches.

Clear by hardware when the activation sequence suceed (flash write sucess, or reset column latch success)

Reset Value= 0000 0000b

Mapping of the Memory Space By default, the user space is accessed by MOVC A, @DPTR instruction for read only.

The column latches space is made accessible by setting the FPS bit in FCON register. Writing is possible from 0000h to FFFFh, address bits 6 to 0 are used to select an address within a page while bits 15 to 7 are used to select the programming address of the page. Setting FPS bit takes precedence on the EXTRAM bit in AUXR register.

The other memory spaces (user, extra row, hardware security) are made accessible in the code segment by programming bits FMOD0 and FMOD1 in FCON register in accordance with Table 15. A MOVC instruction is then used for reading these spaces.

Table 15. FM0 Blocks Select Bits

FMOD1 FMOD0 FM0 Adressable space

0 0 User (0000h-FFFFh)

0 1 Extra Row(FF80h-FFFFh)

1 0 Hardware Security Byte (0000h)

1 1 Column latches reset (note1)

Notes: 1. The column latches reset is a new option introduced in the AT89C51AC3, and is not

available in T89C51CC01/2

Launching Programming FPL3:0 bits in FCON register are used to secure the launch of programming. A specific

sequence must be written in these bits to unlock the write protection and to launch the programming. This sequence is 5xh followed by Axh. Table 16 summarizes the memory spaces to program according to FMOD1:0 bits.

4383D–8051–02/08

AT89C51AC3

Table 16. Programming Spaces

Write to FCON

5 X 0 0 No action

OperationFPL3:0 FPS FMOD1 FMOD0

Write the column latches in user space

Write the column latches in extra row space

User

Extra Row

Hardware

Security

Byte

Reset

Columns

Latches

A X 0 0

5 X 0 1 No action

A X 0 1

5 X 1 0 No action

A X 1 0 Write the fuse bits space

5 X 1 1 No action

A X 1 1 Reset the column latches

Notes: 1. The sequence 5xh and Axh must be executing without instructions between them

otherwise the programming is not executed (see Flash Status Register)

2. The sequence 5xh and Axh must be executed with the same FMOD0 FMOD1 configuration.

3. Interrupts that may occur during programming time must be disabled to avoid any spurious exit of the programming mode.

Status of the Flash Memory The bit FBUSY in FCON register is used to indicate the status of programming.

FBUSY is set when programming is in progress.

The flash programming process is launched the second machine cycle following the sequence 5xh and Axh in FCON. Thus the FBUSY flag should be read by sofware not during the insctruction after the 5xh, Axh sequence but the the second instruction after the 5xh, Axh sequence in FCON (See next example). FBUSY is cleared when the programming is completed.

;*F*************************************************************************

;* NAME: launch_prog

;;***************************************************************************

launch_prog:

MOV FCON, #050h

MOV FCON #0A0h ; Flash Write Sequence

NOP ;Required time before reading busy flag

wait_busy:

MOV A,FCON

JB ACC.0,wait_busy

RET

Selecting FM1 The bit ENBOOT in AUXR1 register is used to map FM1 from F800h to FFFFh.

Loading the Column Latches Any number of data from 1-byte to 128 Bytes can be loaded in the column latches. This

provides the capability to program the whole memory by byte, by page or by any number of Bytes in a page. Data written in the column latches do not have to be in consecutive

4383D–8051–02/08

AT89C51AC3

order. The page address of the last address loaded in the column latches will be used for the whole page.

When programming is launched, an automatic erase of the locations loaded in the column latches is first performed, then programming is effectively done. Thus no page or block erase is needed and only the loaded data are programmed in the corresponding page

Notes: 1. : If no bytes are written in the column latches the SEQERR bit in the FSTA register

will be set.

2. When a flash write sequence is in progress (FBUSY is set) a write sequence to the column latches will be ignored and the content of the column latches at the time of the launch write sequence will be preserved.

3. MOVX @DPTR, A instruction must be used to load the column latches. Never use MOVX @Ri, A instructions.

4. When a programming sequence is launched, Flash bytes corresponding to activated bytes in the column latches are first erased then the bytes in the column latches are copied into the Flash bytes. Flash bytes corresponding to bytes in the column latches not activated (not loaded during the load column latches sequence) will not be erased and written.

The following procedure is used to load the column latches and is summarized in Figure 25:

• Save and Disable interrupt and map the column latch space by setting FPS bit.

• Load the DPTR with the address to load.

• Load Accumulator register with the data to load.

• Execute the MOVX @DPTR, A instruction.

• If needed loop the three last instructions until the page is completely loaded.

• unmap the column latch.

• Restore Interrupt

4383D–8051–02/08

AT89C51AC3

Figure 25. Column Latches Loading Procedure

Column Latches

Data Load

DPTR = Address

ACC = Data

Exec: MOVX @DPTR, A

Last Byte

to load?

Column Latches Mapping

FCON = 08h (FPS=1)

Data memory Mapping

FCON = 00h (FPS = 0)

Save and Disable IT

EA = 0

Restore IT

Note: The last page address used when loading the column latch is the one used to select the

page programming address.

Programming the Flash Spaces

User The following procedure is used to program the User space and is summarized in

Figure 26:

• Load up to one page of data in the column latches from address 0000h to FFFFh.

• Save and Disable the interrupts.

• Launch the programming by writing the data sequence 50h followed by A0h in FCON register (only from FM1). The end of the programming indicated by the FBUSY flag cleared.

• Restore the interrupts.

Extra Row The following procedure is used to program the Extra Row space and is summarized in

Figure 26:

• Load data in the column latches from address FF80h to FFFFh.

• Save and Disable the interrupts.

• Launch the programming by writing the data sequence 52h followed by A2h in FCON register (only from FM1). The end of the programming indicated by the FBUSY flag cleared.

• Restore the interrupts.

4383D–8051–02/08

Figure 26. Flash and Extra Row Programming Procedure

Flash Spaces

Programming

Save and Disable IT

EA = 0

Launch Programming

FCON = 5xh FCON = Axh

End Programming

Restore IT

Column Latches Loading

see Figure 25

FBusy

Cleared?

Clear Mode

FCON = 00h

AT89C51AC3

Hardware Security Byte

The following procedure is used to program the Hardware

Security

Byte space

and is summarized in Figure 27:

• Set FPS and map Hardware byte (FCON = 0x0C)

• Save and disable the interrupts.

• Load DPTR at address 0000h.

• Load Accumulator register with the data to load.

• Execute the MOVX @DPTR, A instruction.

• Launch the programming by writing the data sequence 54h followed by A4h in FCON register (only from FM1). The end of the programming indicated by the FBusy flag cleared.

• Restore the interrupts.

4383D–8051–02/08

AT89C51AC3

Figure 27. Hardware Programming Procedure

Flash Spaces

Programming

Save and Disable IT

EA = 0

Launch Programming

FCON = 54h

FCON = A4h

End Programming

RestoreIT

FBusy

Cleared?

Clear Mode

FCON = 00h

Data Load

DPTR = 00h

ACC = Data

Exec: MOVX @DPTR, A

FCON = 0Ch

Save and Disable IT

EA = 0

End Loading

Restore IT

Reset the Column Latches

Error Reports

Flash Programming Sequence Errors

An automatic reset of the column latches is performed after a successful Flash write sequence. User can also reset the column latches manually, for instance to reload the column latches before writing the Flash. The following procedure is summarized below.

• Save and disable the interrupts.

• Launch the reset by writing the data sequence 56h followed by A6h in FCON register (only from FM1).

• Restore the interrupts.

When a wrong sequence is detected, the SEQERR bit in FSTA register is set. Possible wrong sequence are :

• MOV FCON, 5xh instruction not immediately followed by a MOV FCON, Ax instruction.

• A write Flash sequence is launched while no data were loaded in the column latches

The SEQERR bit can be cleared

• By software

• By hardware when a correct programming sequence is completed

When multiple pages are written into the Flash, the user should check FSTA for errors after each write page sequences, not only at the end of the multiple write pages.

4383D–8051–02/08

AT89C51AC3

Flash Spaces Reading

Flash Spaces Mapping

FCON= 00000xx0b

Data Read

DPTR= Address

ACC= 0

Exec: MOVC A, @A+DPTR

Clear Mode

FCON = 00h

Power Down Request Before entering in Power Down (Set bit PD in PCON register) the user should check that

no write sequence is in progress (check BUSY=0), then check that the column latches are reset (FLOAD=0 in FSTA register. Launch a reset column latches to clear FLOAD if necessary.

Reading the Flash Spaces

User The following procedure is used to read the User space:

• Read one byte in Accumulator by executing MOVC A,@A+DPTR with A+DPTR=read@.

Note: FCON is supposed to be reset when not needed.

Extra Row The following procedure is used to read the Extra Row space and is summarized in

Figure 28:

• Map the Extra Row space by writing 02h in FCON register.

• Read one byte in Accumulator by executing MOVC A,@A+DPTR with A = 0 and DPTR = FF80h to FFFFh.

• Clear FCON to unmap the Extra Row.

Hardware Security Byte

The following procedure is used to read the Hardware

Security

space and is

summarized in Figure 28:

• Map the Hardware Security space by writing 04h in FCON register.

• Read the byte in Accumulator by executing MOVC A,@A+DPTR with A = 0 and DPTR = 0000h.

Figure 28. Clear FCON to unmap the Hardware Security Byte.Reading Procedure

Flash Protection from Parallel Programming

4383D–8051–02/08

The three lock bits in Hardware Security Byte (see "In-System Programming" section) are programmed according to Table 17 provide different level of protection for the onchip code and data located in FM0 and FM1.

The only way to write this bits are the parallel mode. They are set by default to level 4

AT89C51AC3

Table 17. Program Lock Bit

Program Lock Bits

Security

level

1 U U U No program lock features enabled.

2 P U U

3 U P U

4 U U P Same as 3, also external execution is disabled

LB0 LB1 LB2

Protection Description

MOVC instruction executed from external program memory are disabled from fetching code bytes from internal memory, EA is sampled and latched on reset, and further parallel programming of the Flash is disabled.

ISP and software programming with API are still allowed.

Writing EEprom Data from external parallel programmer is disabled but still allowed from internal code execution.

Same as 2, also verify through parallel programming interface is disabled.

Writing And Reading EEPROM Data from external parallel programmer is disabled but still allowed from internal code execution..

Program Lock bits

U: unprogrammed

P: programmed

WARNING: Security level 2 and 3 should only be programmed after Flash and Core verification.

4383D–8051–02/08

Operation Cross Memory Access

Space addressable in read and write are:

• RAM

• ERAM (Expanded RAM access by movx)

• XRAM (eXternal RAM)

• EEPROM DATA

• FM0 ( user flash )

• Hardware byte

• XROW

• Boot Flash

• Flash Column latch

The table below provide the different kind of memory which can be accessed from different code location.

Table 18. Cross Memory Access

AT89C51AC3

Action RAM

boot FLASH

FM0

External memory

EA = 0

or Code Roll

Over

Read OK OK OK OK -

Write - OK

Read OK OK OK OK -

Write - OK (idle) OK

Read - - OK - -

Write - - OK

Note: 1. RWW: Read While Write

XRAM

ERAM Boot FLASH FM0 E² Data

(1)

Hardware

Byte XROW

(1)

- OK

- -

(1)

4383D–8051–02/08

AT89C51AC3

Sharing Instructions

Table 19. Instructions shared

XRAM

Action RAM

Read MOV MOVX MOVX MOVC MOVC MOVC MOVC

Write MOV MOVX MOVX - by cl by cl by cl

ERAM

EEPROM

DATA

Boot

FLASH FM0

Hardware

Byte XROW

Note: by cl : using Column Latch

Table 20. Read MOVX A, @DPTR

EEE bit in

EECON

0 0 X X OK

0 1 X X OK

1 0 X X OK

1 1 X X OK

FPS in

FCON Register ENBOOT EA

XRAM

ERAM

EEPROM

DATA

Table 21. Write MOVX @DPTR,A

EEE bit in

EECON

FPS bit in

FCON Register ENBOOT EA

XRAM

ERAM

EEPROM

Data

Flash

Column

Latch

Flash

Column

Latch

0 0 X X OK

0 1 X

1 0 X X OK

1 1 X

1 OK

0 OK

1 OK

0 OK

4383D–8051–02/08

Table 22. Read MOVC A, @DPTR

AT89C51AC3

Code Execution

From FM0

From FM1

(ENBOOT =1

FCON Register

ENBOOT DPTR FM1 FM0 XROW

0 0000h to FFFFh OK

0 0 X

0 1 X X

1 0 X X X OK

1 1 X

0 0

0 1 X

0 000h to FFFFh OK

0 X NA

1 X OK

0 X NA

0 NA

0000h to F7FF OK

F800h to FFFFh Do not use this configuration

0000 to 007Fh

(1)

See

0000h to F7FF OK

F800h to FFFFh Do not use this configuration

0000h to F7FF OK

F800h to FFFFh OK

0000h to 007h

(2)

See

Hardware

Byte

External

CodeFMOD1 FMOD0 FPS

External code :

EA=0 or Code

Roll Over

1 0 X

1 1 X

X 0 X X X OK

0 NA

000h to FFFFh

1. For DPTR higher than 007Fh only lowest 7 bits are decoded, thus the behavior is the same as for addresses from 0000h to 007Fh

2. For DPTR higher than 007Fh only lowest 7 bits are decoded, thus the behavior is the same as for addresses from 0000h to 007Fh

4383D–8051–02/08

AT89C51AC3

In-System

F800h

FFFFh

64K Bytes

Flash memory

2K Bytes IAP

bootloader

FM0

FM1

Custom Boot Loader

[SBV]00h

FFFFh

FM1 mapped between F800h and FFFFh when API called

0000h

Programming (ISP)

With the implementation of the User Space (FM0) and the Boot Space (FM1) in Flash technology the AT89C51AC3 allows the system engineer the development of applications with a very high level of flexibility. This flexibility is based on the possibility to alter the customer program at any stages of a product’s life:

• Before assembly the 1st personalization of the product by programming in the FM0 and if needed also a customized Boot loader in the FM1. Atmel provide also a standard UART Boot loader by default.

• After assembling on the PCB in its final embedded position by serial mode via the UART.

This In-System Programming (ISP) allows code modification over the total lifetime of the product.

Besides the default Boot loader Atmel provide to the customer also all the needed Application-Programming-Interfaces (API) which are needed for the ISP. The API are located also in the Boot memory.

This allow the customer to have a full use of the 64-Kbyte user memory.

Flash Programming and Erasure

There are three methods of programming the Flash memory:

• The Atmel bootloader located in FM1 is activated by the application. Low level API routines (located in FM1)will be used to program FM0. The interface used for serial downloading to FM0 is the UART. API can be called also by the user’s bootloader located in FM0 at [SBV]00h.

• A further method exists in activating the Atmel boot loader by hardware activation.

• The FM0 can be programmed also by the parallel mode using a programmer.

Figure 29. Flash Memory Mapping

Boot Process

Software Boot Process Example

Many algorithms can be used for the software boot process. Before describing them,

The description of the different flags and Bytes is given below:

4383D–8051–02/08

AT89C51AC3

Boot Loader Jump Bit (BLJB):

- This bit indicates if on RESET the user wants to jump to this application at address

@0000h on FM0 or execute the boot loader at address @F800h on FM1.

- BLJB = 0 on parts delivered with bootloader programmed.

- To read or modify this bit, the APIs are used.

Boot Vector Address (SBV):

- This byte contains the MSB of the user boot loader address in FM0.

- The default value of SBV is FFh (no user boot loader in FM0).

- To read or modify this byte, the APIs are used.

Extra Byte (EB) and Boot Status Byte (BSB):

- These Bytes are reserved for customer use.

- To read or modify these Bytes, the APIs are used.

Hardware Boot Process At the falling edge of RESET, the bit ENBOOT in AUXR1 register is initialized with the

value of Boot Loader Jump Bit (BLJB).

Further at the falling edge of RESET if the following conditions (called Hardware condition) are detected:

• PSEN low,

• EA high,

• ALE high (or not connected).

– After Hardware Condition the FCON register is initialized with the value 00h

and the PC is initialized with F800h (FM1).

The Hardware condition makes the bootloader to be executed, whatever BLJB value is.

If no hardware condition is detected, the FCON register is initialized with the value F0h.

Check of the BLJB value.

• If bit BLJB = 1: User application in FM0 will be started at @0000h (standard reset).

• If bit BLJB = 0: Boot loader will be started at @F800h in FM1.

Note: 1. As PSEN is an output port in normal operating mode (running user applications or

bootloader applications) after reset it is recommended to release PSEN after the falling edge of Reset is signaled. The hardware conditions are sampled at reset signal Falling Edge, thus they can be released at any time when reset input is low.

2. To ensure correct microcontroller startup, the PSEN pin should not be tied to ground during power-on.

4383D–8051–02/08

AT89C51AC3

Figure 30. Hardware Boot Process Algorithm

RESET

Hardware

condition?

BLJB = = 0

bit ENBOOT in AUXR1 register is initialized with BLJB.

Hardware

Software

ENBOOT = 1 PC = F800h

FCON = 00h

FCON = F0h

Boot Loader in FM1

ENBOOT = 0 PC = 0000h

Yes

Application in FM0

Application Programming Interface

XROW Bytes

Several Application Program Interface (API) calls are available for use by an application program to permit selective erasing and programming of Flash pages. All calls are made by functions.

All these APIs are describe in an documentation: "In-System Programing: Flash Library for AT89C51AC3" available on the Atmel web site.

Table 23. XROW Mapping

Description Default Value Address

Copy of the Manufacturer Code 58h 30h

Copy of the Device ID#1: Family code D7h 31h

Copy of the Device ID#2: Memories size and type FFh 60h

Copy of the Device ID#3: Name and Revision FEh 61h

4383D–8051–02/08

AT89C51AC3

Hardware Security Byte

Table 24. Hardware Security Byte

7 6 5 4 3 2 1 0

X2B BLJB - - - LB2 LB1 LB0

Bit

Number

7 X2B

6 BLJB

5-3 -

2-0 LB2:0

Bit

Mnemonic Description

X2 Bit

Set this bit to start in standard mode Clear this bit to start in X2 mode.

Boot Loader JumpBit

- 1: To start the user’s application on next RESET (@0000h) located in FM0,

- 0: To start the boot loader(@F800h) located in FM1.

Reserved

The value read from these bits are indeterminate.

Lock Bits

Default value after erasing chip: FFh

Notes: 1. Only the 4 MSB bits can be accessed by software.

2. The 4 LSB bits can only be accessed by parallel mode.

4383D–8051–02/08

AT89C51AC3

Serial I/O Port

Write SBUF

SBUF

Transmitter

SBUF

Receiver

IB Bus

Mode 0 Transmit

Receive

Shift register

Load SBUF

Read SBUF

Interrupt Request

Serial Port

TXD

RXD

RITIRB8TB8RENSM2SM1SM0/FE

IDLPDGF0GF1POF-SMOD0SMOD

To UART framing error control

SM0 to UART mode control

Set FE bit if stop bit is 0 (framing error)

The AT89C51AC3 I/O serial port is compatible with the I/O serial port in the 80C52. It provides both synchronous and asynchronous communication modes. It operates as a Universal Asynchronous Receiver and Transmitter (UART) in three full-duplex modes (Modes 1, 2 and 3). Asynchronous transmission and reception can occur simultaneously and at different baud rates

Serial I/O port includes the following enhancements:

• Framing error detection

• Automatic address recognition

Figure 31. Serial I/O Port Block Diagram

Framing Error Detection

Figure 32. Framing Error Block Diagram

Framing bit error detection is provided for the three asynchronous modes. To enable the framing bit error detection feature, set SMOD0 bit in PCON register.

When this feature is enabled, the receiver checks each incoming data frame for a valid stop bit. An invalid stop bit may result from noise on the serial lines or from simultaneous transmission by two CPUs. If a valid stop bit is not found, the Framing Error bit (FE) in SCON register bit is set.

The software may examine the FE bit after each reception to check for data errors. Once set, only software or a reset clears the FE bit. Subsequently received frames with valid stop bits cannot clear the FE bit. When the FE feature is enabled, RI rises on the stop bit instead of the last data bit (See Figure 33. and Figure 34.).

4383D–8051–02/08

Figure 33. UART Timing in Mode 1

Data byte

SMOD0=X

Stop

bit

Start

bit

RXD

D7D6D5D4D3D2D1D0

SMOD0=1

SMOD0=0

Data byte Ninth

bit

Stop

bit

Start

bit

RXD

D8D7D6D5D4D3D2D1D0

SMOD0=1

Figure 34. UART Timing in Modes 2 and 3

AT89C51AC3

Automatic Address Recognition

The automatic address recognition feature is enabled when the multiprocessor communication feature is enabled (SM2 bit in SCON register is set).

Implemented in the hardware, automatic address recognition enhances the multiprocessor communication feature by allowing the serial port to examine the address of each incoming command frame. Only when the serial port recognizes its own address will the receiver set the RI bit in the SCON register to generate an interrupt. This ensures that the CPU is not interrupted by command frames addressed to other devices.

If necessary, you can enable the automatic address recognition feature in mode 1. In this configuration, the stop bit takes the place of the ninth data bit. Bit RI is set only when the received command frame address matches the device’s address and is terminated by a valid stop bit.

To support automatic address recognition, a device is identified by a given address and a broadcast address.

Note: The multiprocessor communication and automatic address recognition features cannot

be enabled in mode 0 (i.e. setting SM2 bit in SCON register in mode 0 has no effect).

4383D–8051–02/08

AT89C51AC3

Given Address

Each device has an individual address that is specified in the SADDR register; the SADEN register is a mask byte that contains don’t-care bits (defined by zeros) to form the device’s given address. The don’t-care bits provide the flexibility to address one or more slaves at a time. The following example illustrates how a given address is formed. To address a device by its individual address, the SADEN mask byte must be 1111 1111b. For example:

SADDR0101 0110b SADEN1111 1100b

Given0101 01XXb

Here is an example of how to use given addresses to address different slaves:

Slave A:SADDR1111 0001b

SADEN1111 1010b

Given1111 0X0Xb

Slave B:SADDR1111 0011b

SADEN1111 1001b

Given1111 0XX1b

Slave C:SADDR1111 0011b

SADEN1111 1101b

Given1111 00X1b

The SADEN byte is selected so that each slave may be addressed separately. For slave A, bit 0 (the LSB) is a don’t-care bit; for slaves B and C, bit 0 is a 1. To communicate with slave A only, the master must send an address where bit 0 is clear (e.g. 1111 0000b). For slave A, bit 1 is a 0; for slaves B and C, bit 1 is a don’t care bit. To communicate with slaves A and B, but not slave C, the master must send an address with bits 0 and 1 both set (e.g. 1111 0011b). To communicate with slaves A, B and C, the master must send an address with bit 0 set, bit 1 clear, and bit 2 clear (e.g. 1111 0001b).

Broadcast Address

A broadcast address is formed from the logical OR of the SADDR and SADEN registers with zeros defined as don’t-care bits, e.g.:

SADDR0101 0110b SADEN1111 1100b

SADDR OR SADEN1111 111Xb

The use of don’t-care bits provides flexibility in defining the broadcast address, however in most applications, a broadcast address is FFh. The following is an example of using broadcast addresses:

Slave A:SADDR1111 0001b

SADEN1111 1010b

Given1111 1X11b,

Slave B:SADDR1111 0011b

SADEN1111 1001b

Given1111 1X11B,

Slave C:SADDR=1111 0010b

SADEN1111 1101b

Given1111 1111b

4383D–8051–02/08

AT89C51AC3

For slaves A and B, bit 2 is a don’t care bit; for slave C, bit 2 is set. To communicate with all of the slaves, the master must send an address FFh. To communicate with slaves A and B, but not slave C, the master can send and address FBh.

Registers

Table 25. SCON Register

SCON (S:98h) Serial Control Register

7 6 5 4 3 2 1 0

FE/SM0 SM1 SM2 REN TB8 RB8 TI RI

Bit

Number

7 FE

6 SM1

5 SM2

Bit

Mnemonic Description

Framing Error bit (SMOD0=1

Clear to reset the error state, not cleared by a valid stop bit. Set by hardware when an invalid stop bit is detected.

SM0

Serial port Mode bit 0 (SMOD0=0)

Refer to SM1 for serial port mode selection.

Serial port Mode bit 1

SM0 SM1 Mode Baud Rate 0 0 Shift Register F 0 1 8-bit UART Variable 1 0 9-bit UART F 1 1 9-bit UART Variable

Serial port Mode 2 bit/Multiprocessor Communication Enable bit

Clear to disable multiprocessor communication feature. Set to enable multiprocessor communication feature in mode 2 and 3.

)

XTAL

/12 (or F

/64 or F

/6 in mode X2)

XTAL

/32

XTAL

4 REN

3 TB8

2 RB8

1 TI

0 RI

Reception Enable bit

Clear to disable serial reception. Set to enable serial reception.

Transmitter Bit 8/Ninth bit to transmit in modes 2 and 3

Clear to transmit a logic 0 in the 9th bit. Set to transmit a logic 1 in the 9th bit.

Receiver Bit 8/Ninth bit received in modes 2 and 3

Cleared by hardware if 9th bit received is a logic 0. Set by hardware if 9th bit received is a logic 1.

Transmit Interrupt flag

Clear to acknowledge interrupt. Set by hardware at the end of the 8th bit time in mode 0 or at the beginning of the stop bit in the other modes.

Receive Interrupt flag

Clear to acknowledge interrupt. Set by hardware at the end of the 8th bit time in mode 0, see Figure 33. and Figure 34. in the other modes.

Reset Value = 0000 0000b Bit addressable

4383D–8051–02/08

AT89C51AC3

Table 26. SADEN Register

SADEN (S:B9h) Slave Address Mask Register

7 6 5 4 3 2 1 0

– – – – – – – –

Bit

Number

7-0

Bit

Mnemonic Description

Mask Data for Slave Individual Address

Reset Value = 0000 0000b Not bit addressable

Table 27. SADDR Register

SADDR (S:A9h) Slave Address Register

7 6 5 4 3 2 1 0

– – – – – – – –

Bit

Number

7-0

Bit

Mnemonic Description

Slave Individual Address

Reset Value = 0000 0000b Not bit addressable

Table 28. SBUF Register

SBUF (S:99h) Serial Data Buffer

7 6 5 4 3 2 1 0

– – – – – – – –

Bit

Number

7-0

Bit

Mnemonic Description

Data sent/received by Serial I/O Port

Reset Value = 0000 0000b Not bit addressable

4383D–8051–02/08

AT89C51AC3

Table 29. PCON Register

PCON (S:87h) Power Control Register

7 6 5 4 3 2 1 0

SMOD1 SMOD0 – POF GF1 GF0 PD IDL

Bit

Number

7 SMOD1

6 SMOD0

5 -

4 POF

3 GF1

2 GF0

1 PD

0 IDL

Bit

Mnemonic Description

Serial port Mode bit 1

Set to select double baud rate in mode 1, 2 or 3.

Serial port Mode bit 0

Clear to select SM0 bit in SCON register. Set to select FE bit in SCON register.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Power-Off Flag

Clear to recognize next reset type. Set by hardware when VCC rises from 0 to its nominal voltage. Can also be set by software.

General-purpose Flag

Cleared by user for general-purpose usage. Set by user for general-purpose usage.

General-purpose Flag

Cleared by user for general-purpose usage. Set by user for general-purpose usage.

Power-Down mode bit

Cleared by hardware when reset occurs. Set to enter power-down mode.

Idle mode bit

Clear by hardware when interrupt or reset occurs. Set to enter idle mode.

4383D–8051–02/08

Reset Value = 00X1 0000b Not bit addressable

AT89C51AC3

Timers/Counters

The AT89C51AC3 implements two general-purpose, 16-bit Timers/Counters. Such are identified as Timer 0 and Timer 1, and can be independently configured to operate in a variety of modes as a Timer or an event Counter. When operating as a Timer, the Timer/Counter runs for a programmed length of time, then issues an interrupt request. When operating as a Counter, the Timer/Counter counts negative transitions on an external pin. After a preset number of counts, the Counter issues an interrupt request. The various operating modes of each Timer/Counter are described in the following sections.

Timer/Counter Operations

A basic operation is Timer registers THx and TLx (x = 0, 1) connected in cascade to form a 16-bit Timer. Setting the run control bit (TRx) in TCON register (see Figure 30) turns the Timer on by allowing the selected input to increment TLx. When TLx overflows it increments THx; when THx overflows it sets the Timer overflow flag (TFx) in TCON register. Setting the TRx does not clear the THx and TLx Timer registers. Timer registers can be accessed to obtain the current count or to enter preset values. They can be read at any time but TRx bit must be cleared to preset their values, otherwise the behavior of the Timer/Counter is unpredictable.

The C/Tx# control bit selects Timer operation or Counter operation by selecting the divided-down peripheral clock or external pin Tx as the source for the counted signal. TRx bit must be cleared when changing the mode of operation, otherwise the behavior of the Timer/Counter is unpredictable.

For Timer operation (C/Tx# = 0), the Timer register counts the divided-down peripheral clock. The Timer register is incremented once every peripheral cycle (6 peripheral clock periods). The Timer clock rate is F

/6, i.e. F

PER

/12 in standard mode or F

OSC

/6 in X2

mode.

For Counter operation (C/Tx# = 1), the Timer register counts the negative transitions on the Tx external input pin. The external input is sampled every peripheral cycles. When the sample is high in one cycle and low in the next one, the Counter is incremented. Since it takes 2 cycles (12 peripheral clock periods) to recognize a negative transition, the maximum count rate is F

/12, i.e. F

PER

/24 in standard mode or F

OSC

/12 in X2

OSC

mode. There are no restrictions on the duty cycle of the external input signal, but to ensure that a given level is sampled at least once before it changes, it should be held for at least one full peripheral cycle.

Timer 0

Timer 0 functions as either a Timer or event Counter in four modes of operation. Figure 35 to Figure 38 show the logical configuration of each mode.

Timer 0 is controlled by the four lower bits of TMOD register (see Figure 31) and bits 0, 1, 4 and 5 of TCON register (see Figure 30). TMOD register selects the method of Timer gating (GATE0), Timer or Counter operation (T/C0#) and mode of operation (M10 and M00). TCON register provides Timer 0 control functions: overflow flag (TF0), run control bit (TR0), interrupt flag (IE0) and interrupt type control bit (IT0).

For normal Timer operation (GATE0 = 0), setting TR0 allows TL0 to be incremented by the selected input. Setting GATE0 and TR0 allows external pin INT0# to control Timer operation.

Timer 0 overflow (count rolls over from all 1s to all 0s) sets TF0 flag generating an interrupt request.

It is important to stop Timer/Counter before changing mode.

4383D–8051–02/08

AT89C51AC3

FTx

CLOCK

TRx

TCON reg

TFx

TCON reg

GATEx

TMOD reg

Overflow

Timer x Interrupt Request

C/Tx#

TMOD reg

TLx

(5 bits)

THx

(8 bits)

INTx#

See the “Clock” section

TRx

TCON reg

TFx

TCON reg

GATEx

TMOD reg

Overflow

Timer x Interrupt Request

C/Tx#

TMOD reg

TLx

(8 bits)

THx

(8 bits)

INTx#

FTx

CLOCK

See the “Clock” section

Mode 0 (13-bit Timer) Mode 0 configures Timer 0 as an 13-bit Timer which is set up as an 8-bit Timer (TH0

register) with a modulo 32 prescaler implemented with the lower five bits of TL0 register (see Figure 35). The upper three bits of TL0 register are indeterminate and should be ignored. Prescaler overflow increments TH0 register.

Figure 35. Timer/Counter x (x = 0 or 1) in Mode 0

Mode 1 (16-bit Timer) Mode 1 configures Timer 0 as a 16-bit Timer with TH0 and TL0 registers connected in

cascade (see Figure 36). The selected input increments TL0 register.

Figure 36. Timer/Counter x (x = 0 or 1) in Mode 1

4383D–8051–02/08

AT89C51AC3

Mode 2 (8-bit Timer with Auto-

TRx

TCON reg

TFx

TCON reg

GATEx

TMOD reg

Overflow

Timer x Interrupt Request

C/Tx#

TMOD reg

TLx

(8 bits)

THx

(8 bits)

INTx#

FTx

CLOCK

See the “Clock” section

TR0

TCON.4

TF0

TCON.5

INT0#

GATE0

TMOD.3

Overflow

Timer 0 Interrupt Request

C/T0#

TMOD.2

TL0

(8 bits)

TR1

TCON.6

TH0

(8 bits)

TF1

TCON.7

Overflow

Timer 1 Interrupt Request

FTx

CLOCK

FTx

CLOCK

See the “Clock” section

Reload)

Mode 2 configures Timer 0 as an 8-bit Timer (TL0 register) that automatically reloads from TH0 register (see Figure 37). TL0 overflow sets TF0 flag in TCON register and reloads TL0 with the contents of TH0, which is preset by software. When the interrupt request is serviced, hardware clears TF0. The reload leaves TH0 unchanged. The next reload value may be changed at any time by writing it to TH0 register.

Figure 37. Timer/Counter x (x = 0 or 1) in Mode 2

Mode 3 (Two 8-bit Timers) Mode 3 configures Timer 0 such that registers TL0 and TH0 operate as separate 8-bit

Timers (see Figure 38). This mode is provided for applications requiring an additional 8bit Timer or Counter. TL0 uses the Timer 0 control bits C/T0# and GATE0 in TMOD register, and TR0 and TF0 in TCON register in the normal manner. TH0 is locked into a Timer function (counting F

/6) and takes over use of the Timer 1 interrupt (TF1) and

PER

run control (TR1) bits. Thus, operation of Timer 1 is restricted when Timer 0 is in mode

Figure 38. Timer/Counter 0 in Mode 3: Two 8-bit Counters

4383D–8051–02/08

AT89C51AC3

Timer 1

Timer 1 is identical to Timer 0 excepted for Mode 3 which is a hold-count mode. The following comments help to understand the differences:

• Timer 1 functions as either a Timer or event Counter in three modes of operation. Figure 35 to Figure 37 show the logical configuration for modes 0, 1, and 2. Timer 1’s mode 3 is a hold-count mode.

• Timer 1 is controlled by the four high-order bits of TMOD register (see Figure 31) and bits 2, 3, 6 and 7 of TCON register (see Figure 30). TMOD register selects the method of Timer gating (GATE1), Timer or Counter operation (C/T1#) and mode of operation (M11 and M01). TCON register provides Timer 1 control functions: overflow flag (TF1), run control bit (TR1), interrupt flag (IE1) and interrupt type control bit (IT1).

• Timer 1 can serve as the Baud Rate Generator for the Serial Port. Mode 2 is best suited for this purpose.

• For normal Timer operation (GATE1 = 0), setting TR1 allows TL1 to be incremented by the selected input. Setting GATE1 and TR1 allows external pin INT1# to control Timer operation.

• Timer 1 overflow (count rolls over from all 1s to all 0s) sets the TF1 flag generating an interrupt request.

• When Timer 0 is in mode 3, it uses Timer 1’s overflow flag (TF1) and run control bit (TR1). For this situation, use Timer 1 only for applications that do not require an interrupt (such as a Baud Rate Generator for the Serial Port) and switch Timer 1 in and out of mode 3 to turn it off and on.

• It is important to stop Timer/Counter before changing mode.

Mode 0 (13-bit Timer) Mode 0 configures Timer 1 as a 13-bit Timer, which is set up as an 8-bit Timer (TH1 reg-

ister) with a modulo-32 prescaler implemented with the lower 5 bits of the TL1 register (see Figure 35). The upper 3 bits of TL1 register are ignored. Prescaler overflow increments TH1 register.

Mode 1 (16-bit Timer) Mode 1 configures Timer 1 as a 16-bit Timer with TH1 and TL1 registers connected in

cascade (see Figure 36). The selected input increments TL1 register.

Mode 2 (8-bit Timer with AutoReload)

Mode 3 (Halt) Placing Timer 1 in mode 3 causes it to halt and hold its count. This can be used to halt

Mode 2 configures Timer 1 as an 8-bit Timer (TL1 register) with automatic reload from TH1 register on overflow (see Figure 37). TL1 overflow sets TF1 flag in TCON register and reloads TL1 with the contents of TH1, which is preset by software. The reload leaves TH1 unchanged.

Timer 1 when TR1 run control bit is not available i.e. when Timer 0 is in mode 3.

4383D–8051–02/08

AT89C51AC3

Interrupt

TF0

TCON.5

ET0

IEN0.1

Timer 0 Interrupt Request

TF1

TCON.7

ET1

IEN0.3

Timer 1 Interrupt Request

Each Timer handles one interrupt source that is the timer overflow flag TF0 or TF1. This flag is set every time an overflow occurs. Flags are cleared when vectoring to the Timer interrupt routine. Interrupts are enabled by setting

ETx

bit in IEN0 register. This assumes

interrupts are globally enabled by setting EA bit in IEN0 register.

Figure 39. Timer Interrupt System

Registers

Table 30. TCON Register

TCON (S:88h) Timer/Counter Control Register

7 6 5 4 3 2 1 0

TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0

Bit

Number

7 TF1

6 TR1

5 TF0

4 TR0

3 IE1

Bit

Mnemonic Description

Timer 1 Overflow Flag

Cleared by hardware when processor vectors to interrupt routine. Set by hardware on Timer/Counter overflow, when Timer 1 register overflows.

Timer 1 Run Control Bit

Clear to turn off Timer/Counter 1. Set to turn on Timer/Counter 1.

Timer 0 Overflow Flag

Cleared by hardware when processor vectors to interrupt routine. Set by hardware on Timer/Counter overflow, when Timer 0 register overflows.

Timer 0 Run Control Bit

Clear to turn off Timer/Counter 0. Set to turn on Timer/Counter 0.

Interrupt 1 Edge Flag

Cleared by hardware when interrupt is processed if edge-triggered (see IT1). Set by hardware when external interrupt is detected on INT1# pin.

2 IT1

1 IE0

0 IT0

Reset Value = 0000 0000b

Interrupt 1 Type Control Bit

Clear to select low level active (level triggered) for external interrupt 1 (INT1#). Set to select falling edge active (edge triggered) for external interrupt 1.

Interrupt 0 Edge Flag

Cleared by hardware when interrupt is processed if edge-triggered (see IT0). Set by hardware when external interrupt is detected on INT0# pin.

Interrupt 0 Type Control Bit

Clear to select low level active (level triggered) for external interrupt 0 (INT0#). Set to select falling edge active (edge triggered) for external interrupt 0.

4383D–8051–02/08

AT89C51AC3

Table 31. TMOD Register

TMOD (S:89h) Timer/Counter Mode Control Register

7 6 5 4 3 2 1 0

GATE1 C/T1# M11 M01 GATE0 C/T0# M10 M00

Bit

Number

7 GATE1

6 C/T1#

5 M11

4 M01

3 GATE0

2 C/T0#

1 M10

Bit

Mnemonic Description

Timer 1 Gating Control Bit

Clear to enable Timer 1 whenever TR1 bit is set. Set to enable Timer 1 only while INT1# pin is high and TR1 bit is set.

Timer 1 Counter/Timer Select Bit

Clear for Timer operation: Timer 1 counts the divided-down system clock. Set for Counter operation: Timer 1 counts negative transitions on external pin T1.

Timer 1 Mode Select Bits

M11 M01 Operating mode

0 0 Mode 0: 8-bit Timer/Counter (TH1) with 5-bit prescaler (TL1). 0 1 Mode 1: 16-bit Timer/Counter.

1 0 Mode 2: 8-bit auto-reload Timer/Counter (TL1) 1 1 Mode 3: Timer 1 halted. Retains count

Timer 0 Gating Control Bit

Clear to enable Timer 0 whenever TR0 bit is set. Set to enable Timer/Counter 0 only while INT0# pin is high and TR0 bit is set.

Timer 0 Counter/Timer Select Bit

Clear for Timer operation: Timer 0 counts the divided-down system clock. Set for Counter operation: Timer 0 counts negative transitions on external pin T0.

Timer 0 Mode Select Bit

M10 M00 Operating mode

0 0 Mode 0: 8-bit Timer/Counter (TH0) with 5-bit prescaler (TL0). 0 1 Mode 1: 16-bit Timer/Counter.

M00

1 0 Mode 2: 8-bit auto-reload Timer/Counter (TL0) 1 1 Mode 3: TL0 is an 8-bit Timer/Counter

TH0 is an 8-bit Timer using Timer 1’s TR0 and TF0 bits.

(1)

(2)

4383D–8051–02/08

1. Reloaded from TH1 at overflow.

2. Reloaded from TH0 at overflow.

Reset Value = 0000 0000b

AT89C51AC3

Table 32. TH0 Register

TH0 (S:8Ch) Timer 0 High Byte Register

7 6 5 4 3 2 1 0

– – – – – – – –

Bit

Number

7:0

Bit

Mnemonic Description

High Byte of Timer 0.

Reset Value = 0000 0000b

Table 33. TL0 Register

TL0 (S:8Ah) Timer 0 Low Byte Register

7 6 5 4 3 2 1 0

– – – – – – – –

Bit

Number

7:0

Bit

Mnemonic Description

Low Byte of Timer 0.

Reset Value = 0000 0000b

Table 34. TH1 Register

TH1 (S:8Dh) Timer 1 High Byte Register

7 6 5 4 3 2 1 0

– – – – – – – –

Bit

Number

7:0

Bit

Mnemonic Description

High Byte of Timer 1.

Reset Value = 0000 0000b

4383D–8051–02/08

AT89C51AC3

Table 35. TL1 Register

TL1 (S:8Bh) Timer 1 Low Byte Register

7 6 5 4 3 2 1 0

– – – – – – – –

Bit

Number

7:0

Bit

Mnemonic Description

Low Byte of Timer 1.

Reset Value = 0000 0000b

4383D–8051–02/08

AT89C51AC3

Timer 2

(DOWN COUNTING RELOAD VALUE)

TF2

EXF2

TH2

(8-bit)

TL2

(

8-bit)

RCAP2H

(8-bit)

RCAP2L

(8-bit)

FFh

(8-bit)

FFh

(

8-bit)

TOGGLE

(UP COUNTING RELOAD VALUE)

TIMER 2

INTERRUPT

T2CONreg

T2EX:

1=UP

2=DOWN

CT/2

T2CON.1

TR2

T2CON.2

FT2

CLOCK

see section “Clock”

The AT89C51AC3 timer 2 is compatible with timer 2 in the 80C52.

It is a 16-bit timer/counter: the count is maintained by two eight-bit timer registers, TH2 and TL2 that are cascade- connected. It is controlled by T2CON register (See Table ) and T2MOD register (See Table 38). Timer 2 operation is similar to Timer 0 and Timer

1. C/T2 selects F

/6 (timer operation) or external pin T2 (counter operation) as

T2 clock

timer clock. Setting TR2 allows TL2 to be incremented by the selected input.

Timer 2 includes the following enhancements:

• Auto-reload mode (up or down counter)

• Programmable clock-output

Auto-Reload Mode

The auto-reload mode configures timer 2 as a 16-bit timer or event counter with automatic reload. This feature is controlled by the DCEN bit in T2MOD register (See Table 38). Setting the DCEN bit enables timer 2 to count up or down as shown in Figure 40. In this mode the T2EX pin controls the counting direction.

When T2EX is high, timer 2 counts up. Timer overflow occurs at FFFFh which sets the TF2 flag and generates an interrupt request. The overflow also causes the 16-bit value in RCAP2H and RCAP2L registers to be loaded into the timer registers TH2 and TL2.

When T2EX is low, timer 2 counts down. Timer underflow occurs when the count in the timer registers TH2 and TL2 equals the value stored in RCAP2H and RCAP2L registers. The underflow sets TF2 flag and reloads FFFFh into the timer registers.

The EXF2 bit toggles when timer 2 overflow or underflow, depending on the direction of the count. EXF2 does not generate an interrupt. This bit can be used to provide 17-bit resolution.

Figure 40. Auto-Reload Mode Up/Down Counter

4383D–8051–02/08

AT89C51AC3

Clock O utFre que ncy–

FT 2cl ock

4 65536 RCA P2H– RCA P2L⁄( )×

-----------------------------------------------------------------------------------------

EXEN2

EXF2

OVERFLOW

T2EX

TH2

(8-bit)

TL2

(8-bit)

TIMER 2

RCAP2H

(8-bit)

RCAP2L

(8-bit)

T2OE

T2CON reg

T2MOD reg

INTERRUPT

TR2

T2CON.2

FT2

CLOCK

Q D

Toggle

Programmable ClockOutput

In clock-out mode, timer 2 operates as a 50%-duty-cycle, programmable clock generator (See Figure 41). The input clock increments TL2 at frequency F

/2. The timer

OSC

repeatedly counts to overflow from a loaded value. At overflow, the contents of RCAP2H and RCAP2L registers are loaded into TH2 and TL2. In this mode, timer 2 overflows do not generate interrupts. The formula gives the clock-out frequency depending on the system oscillator frequency and the value in the RCAP2H and RCAP2L registers:

For a 16 MHz system clock in x1 mode, timer 2 has a programmable frequency range of 61 Hz (F

OSC

16)

to 4 MHz (F

/4). The generated clock signal is brought out to T2 pin

OSC

(P1.0).

Timer 2 is programmed for the clock-out mode as follows:

• Set T2OE bit in T2MOD register.

• Clear C/T2 bit in T2CON register.

• Determine the 16-bit reload value from the formula and enter it in RCAP2H/RCAP2L registers.

• Enter a 16-bit initial value in timer registers TH2/TL2. It can be the same as the reload value or different depending on the application.

• To start the timer, set TR2 run control bit in T2CON register.

Figure 41. Clock-Out Mode

It is possible to use timer 2 as a baud rate generator and a clock generator simultane ous ly. For thi s co nfi gur ation, the bau d rates and clock frequencies are not independent since both functions use the values in the RCAP2H and RCAP2L registers.

4383D–8051–02/08

AT89C51AC3

Registers

Table 36. T2CON Register

T2CON (S:C8h) Timer 2 Control Register

7 6 5 4 3 2 1 0

TF2 EXF2 RCLK TCLK EXEN2 TR2 C/T2# CP/RL2#

Bit

Number

7 TF2

6 EXF2

5 RCLK

4 TCLK

3 EXEN2

2 TR2

Bit

Mnemonic Description

Timer 2 Overflow Flag

TF2 is not set if RCLK=1 or TCLK = 1. Must be cleared by software. Set by hardware on timer 2 overflow.

Timer 2 External Flag

Set when a capture or a reload is caused by a negative transition on T2EX pin if EXEN2=1. Set to cause the CPU to vector to timer 2 interrupt routine when timer 2 interrupt is enabled. Must be cleared by software.

Receive Clock bit

Clear to use timer 1 overflow as receive clock for serial port in mode 1 or 3. Set to use timer 2 overflow as receive clock for serial port in mode 1 or 3.

Transmit Clock bit

Clear to use timer 1 overflow as transmit clock for serial port in mode 1 or 3. Set to use timer 2 overflow as transmit clock for serial port in mode 1 or 3.

Timer 2 External Enable bit

Clear to ignore events on T2EX pin for timer 2 operation. Set to cause a capture or reload when a negative transition on T2EX pin is detected, if timer 2 is not used to clock the serial port.

Timer 2 Run Control bit

Clear to turn off timer 2. Set to turn on timer 2.

1 C/T2#

0 CP/RL2#

Timer/Counter 2 Select bit

Clear for timer operation (input from internal clock system: F Set for counter operation (input from T2 input pin).

Timer 2 Capture/Reload bit

If RCLK=1 or TCLK=1, CP/RL2# is ignored and timer is forced to auto-reload on timer 2 overflow. Clear to auto-reload on timer 2 overflows or negative transitions on T2EX pin if EXEN2=1. Set to capture on negative transitions on T2EX pin if EXEN2=1.

Reset Value = 0000 0000b Bit addressable

OSC

4383D–8051–02/08

AT89C51AC3

Table 37. T2MOD Register

T2MOD (S:C9h) Timer 2 Mode Control Register

7 6 5 4 3 2 1 0

- - - - - - T2OE DCEN

Bit

Number

7 -

6 -

5 -

4 -

3 -

2 -

1 T2OE

0 DCEN

Bit

Mnemonic Description

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Timer 2 Output Enable bit

Clear to program P1.0/T2 as clock input or I/O port. Set to program P1.0/T2 as clock output.

Down Counter Enable bit

Clear to disable timer 2 as up/down counter. Set to enable timer 2 as up/down counter.

Reset Value = XXXX XX00b Not bit addressable

4383D–8051–02/08

Table 38. TH2 Register

TH2 (S:CDh) Timer 2 High Byte Register

7 6 5 4 3 2 1 0

- - - - - - - -

Bit

Number

7-0 High Byte of Timer 2.

Bit

Mnemonic Description

Reset Value = 0000 0000b Not bit addressable

AT89C51AC3

Table 39. TL2 Register

TL2 (S:CCh) Timer 2 Low Byte Register

7 6 5 4 3 2 1 0

- - - - - - - -

Bit

Number

7-0 Low Byte of Timer 2.

Bit

Mnemonic Description

Reset Value = 0000 0000b Not bit addressable

Table 40. RCAP2H Register

RCAP2H (S:CBh) Timer 2 Reload/Capture High Byte Register

7 6 5 4 3 2 1 0

- - - - - - - -

Bit

Number

7-0 High Byte of Timer 2 Reload/Capture.

Bit

Mnemonic Description

Reset Value = 0000 0000b Not bit addressable

Table 41. RCAP2L Register

RCAP2L (S:CAH) T

IMER

2 REload/Capture Low Byte Register

7 6 5 4 3 2 1 0

- - - - - - - -

Bit

Number

7-0 Low Byte of Timer 2 Reload/Capture.

Bit

Mnemonic Description

Reset Value = 0000 0000b Not bit addressable

4383D–8051–02/08

AT89C51AC3

CPU and Peripheral Clock

Fwd

CLOCK

WDTPRG

Watchdog Timer

Figure 42. Watchdog Timer

AT89C51AC3 contains a powerful programmable hardware Watchdog Timer (WDT) that automatically resets the chip if it software fails to reset the WDT before the selected time interval has elapsed. It permits large Time-Out ranking from 16ms to 2s @Fosc = 12MHz in X1 mode.

This WDT consists of a 14-bit counter plus a 7-bit programmable counter, a Watchdog Timer reset register (WDTRST) and a Watchdog Timer programming (WDTPRG) register. When exiting reset, the WDT is -by default- disable.

To enable the WDT, the user has to write the sequence 1EH and E1H into WDTRST register no instruction in between. When the Watchdog Timer is enabled, it will increment every machine cycle while the oscillator is running and there is no way to disable the WDT except through reset (either hardware reset or WDT overflow reset). When WDT overflows, it will generate an output RESET pulse at the RST pin. The RESET pulse duration is 96xT

, where T

OSC

=1/F

. To make the best use of the WDT, it

OSC

should be serviced in those sections of code that will periodically be executed within the time required to prevent a WDT reset

Note: When the Watchdog is enable it is impossible to change its period.

Fwd Clock

RESET

WDTRST

Enable

14-bit COUNTER

Decoder

Control

7-bit COUNTER

Outputs

RESET

4383D–8051–02/08

AT89C51AC3

Watchdog Programming

FT ime O ut

12 2142

Sv a lu e

×( ) 1–( )×

-----------------------------------------------------------------

=–

The three lower bits (S0, S1, S2) located into WDTPRG register permit to program the WDT duration.

Table 42. Machine Cycle Count

S2 S1 S0 Machine Cycle Count

0 0 0 214 - 1

0 0 1 215 - 1

0 1 0 2

0 1 1 217 - 1

1 0 0 218 - 1

1 0 1 219 - 1

1 1 0 220 - 1

1 1 1 221 - 1

- 1

To compute WD Time-Out, the following formula is applied:

Note: Svalue represents the decimal value of (S2 S1 S0)

The following table outlines the time-out value for Fosc

= 12 MHz in X1 mode

XTAL

Table 43. Time-Out Computation

S2 S1 S0 Fosc = 12 MHz Fosc = 16 MHz Fosc = 20 MHz

0 0 0 16.38 ms 12.28 ms 9.82 ms

0 0 1 32.77 ms 24.57 ms 19.66 ms

0 1 0 65.54 ms 49.14 ms 39.32 ms

0 1 1 131.07 ms 98.28 ms 78.64 ms

1 0 0 262.14 ms 196.56 ms 157.28 ms

1 0 1 524.29 ms 393.12 ms 314.56 ms

1 1 0 1.05 s 786.24 ms 629.12 ms

1 1 1 2.10 s 1.57 s 1.25 s

4383D–8051–02/08

AT89C51AC3

Watchdog Timer During Power-down Mode and Idle

In Power-down mode the oscillator stops, which means the WDT also stops. While in Power-down mode, the user does not need to service the WDT. There are 2 methods of exiting Power-down 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, the Watchdog is disabled. Exiting Power-down with an interrupt is significantly different. The interrupt shall be 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.

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

In the Idle mode, the oscillator continues to run. To prevent the WDT from resetting AT89C51AC3 while in Idle mode, the user should always set up a timer that will periodically exit Idle, service the WDT, and re-enter Idle mode.

WDTPRG (S:A7h) Watchdog Timer Duration Programming Register

7 6 5 4 3 2 1 0

– – – – – S2 S1 S0

Bit

Number

7 -

6 -

5 -

4 -

3 -

2 S2

1 S1

0 S0

Bit

Mnemonic Description

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Watchdog Timer Duration selection bit 2

Work in conjunction with bit 1 and bit 0.

Watchdog Timer Duration selection bit 1

Work in conjunction with bit 2 and bit 0.

Watchdog Timer Duration selection bit 0

Work in conjunction with bit 1 and bit 2.

Reset Value = XXXX X000b

4383D–8051–02/08

AT89C51AC3

Table 45. WDTRST Register

WDTRST (S:A6h Write only) Watchdog Timer Enable Register

7 6 5 4 3 2 1 0

– – – – – – – –

Bit

Number

7 - Watchdog Control Value

Bit

Mnemonic Description

Reset Value = 1111 1111b

Note: The WDRST register is used to reset/enable the WDT by writing 1EH then E1H in

sequence without instruction between these two sequences.

4383D–8051–02/08

AT89C51AC3

Slave 1

MISO

MOSI

SCK

MISO MOSI SCK SS

PORT

0 1 2 3

Slave 3

MISO

MOSI

SCK

Slave 4

MISO

MOSI

SCK

Slave 2

MISO

MOSI

SCK

VDD

Master

Serial Port Interface (SPI)

Features

Signal Description

The Serial Peripheral Interface Module (SPI) allows full-duplex, synchronous, serial communication between the MCU and peripheral devices, including other MCUs.

Features of the SPI Module include the following:

• Full-duplex, three-wire synchronous transfers

• Master or Slave operation

• Six programmable Master clock rates in master mode

• Serial clock with programmable polarity and phase

• Master Mode fault error flag with MCU interrupt capability

Figure 43 shows a typical SPI bus configuration using one Master controller and many Slave peripherals. The bus is made of three wires connecting all the devices.

Figure 43. SPI Master/Slaves Interconnection

The Master device selects the individual Slave devices by using four pins of a parallel port to control the four SS pins of the Slave devices.

Master Output Slave Input (MOSI)

This 1-bit signal is directly connected between the Master Device and a Slave Device. The MOSI line is used to transfer data in series from the Master to the Slave. Therefore, it is an output signal from the Master, and an input signal to a Slave. A Byte (8-bit word) is transmitted most significant bit (MSB) first, least significant bit (LSB) last.

Master Input Slave Output (MISO)

This 1-bit signal is directly connected between the Slave Device and a Master Device. The MISO line is used to transfer data in series from the Slave to the Master. Therefore, it is an output signal from the Slave, and an input signal to the Master. A Byte (8-bit word) is transmitted most significant bit (MSB) first, least significant bit (LSB) last.

SPI Serial Clock (SCK) This signal is used to synchronize the data transmission both in and out of the devices

through their MOSI and MISO lines. It is driven by the Master for eight clock cycles

Slave Select (SS) Each Slave peripheral is selected by one Slave Select pin (SS). This signal must stay

which allows to exchange one Byte on the serial lines.

low for any message for a Slave. It is obvious that only one Master (SS high level) can drive the network. The Master may select each Slave device by software through port pins (Figure 44). To prevent bus conflicts on the MISO line, only one slave should be selected at a time by the Master for a transmission.

4383D–8051–02/08

AT89C51AC3

In a Master configuration, the SS line can be used in conjunction with the MODF flag in the SPI Status register (SPSCR) to prevent multiple masters from driving MOSI and SCK (see Error conditions).

A high level on the SS pin puts the MISO line of a Slave SPI in a high-impedance state.

The SS pin could be used as a general-purpose if the following conditions are met:

• The device is configured as a Master and the SSDIS control bit in SPCON is set. This kind of configuration can be found when only one Master is driving the network and there is no way that the SS pin could be pulled low. Therefore, the MODF flag in the SPSCR will never be set

• The Device is configured as a Slave with CPHA and SSDIS control bits set

(1)

(2)

. This kind of configuration can happen when the system includes one Master and one Slave only. Therefore, the device should always be selected and there is no reason that the Master uses the SS pin to select the communicating Slave device.

Note: 1. Clearing SSDIS control bit does not clear MODF.

2. Special care should be taken not to set SSDIS control bit when CPHA =’0’ because in this mode, the SS is used to start the transmission.

Baud Rate In Master mode, the baud rate can be selected from a baud rate generator which is con-

trolled by three bits in the SPCON register: SPR2, SPR1 and SPR0.The Master clock is selected from one of seven clock rates resulting from the division of the internal clock by 4, 8, 16, 32, 64 or 128.

Table 46 gives the different clock rates selected by SPR2:SPR1:SPR0.

In Slave mode, the maximum baud rate allowed on the SCK input is limited to F

Table 46. SPI Master Baud Rate Selection

SPR2 SPR1 SPR0 Clock Rate Baud Rate Divisor (BD)

0 0 0 Don’t Use No BRG

0 0 1 F

0 1 0 F

0 1 1 F

1 0 0 F

1 0 1 F

1 1 0 F

1 1 1 Don’t Use No BRG

CLK PERIPH

/4 4

/8 8

/16 16

/32 32

/64 64

/128 128

sys

4383D–8051–02/08

AT89C51AC3

Shift Register

234567

Internal Bus

Pin Control Logic

MISO

MOSI

SCK

M S

Clock Logic

SPI Interrupt

8-bit bus

1-bit signal

FCLK

Receive Data Register

SPDAT

SPI Control

Transmit Data Register

- MODFSPIF OVR SPTE UARTM

SPTEIE

MODFIE

SPSCR

SPEN MSTRSPR2 SSDIS CPOL CPHA SPR1 SPR0

SPCON

Request

PERIPH

Functional Description

Figure 44 shows a detailed structure of the SPI Module.

Figure 44. SPI Module Block Diagram

Operating Modes The Serial Peripheral Interface can be configured in one of the two modes: Master mode

or Slave mode. The configuration and initialization of the SPI Module is made through two registers:

• The Serial Peripheral Control register (SPCON)

• The Serial Peripheral Status and Control Register (SPSCR)

Once the SPI is configured, the data exchange is made using:

• The Serial Peripheral DATa register (SPDAT)

During an SPI transmission, data is simultaneously transmitted (shifted out serially) and received (shifted in serially). A serial clock line (SCK) synchronizes shifting and sampling on the two serial data lines (MOSI and MISO). A Slave Select line (SS) allows individual selection of a Slave SPI device; Slave devices that are not selected do not interfere with SPI bus activities.

4383D–8051–02/08

AT89C51AC3

When the Master device transmits data to the Slave device via the MOSI line, the Slave

8-bit Shift register

SPI

Clock Generator

Master MCU

8-bit Shift register

MISOMISO

MOSI

SCK SCK

VSS

VDD

SSSS

Slave MCU

device responds by sending data to the Master device via the MISO line. This implies full-duplex transmission with both data out and data in synchronized with the same clock (Figure 45).

Figure 45. Full-Duplex Master-Slave Interconnection

Master Mode The SPI operates in Master mode when the Master bit, MSTR

is set. Only one Master SPI device can initiate transmissions. Software begins the transmission from a Master SPI Module by writing to the Serial Peripheral Data Register (SPDAT). If the shift register is empty, the Byte is immediately transferred to the shift register. The Byte begins shifting out on MOSI pin under the control of the serial clock, SCK. Simultaneously, another Byte shifts in from the Slave on the Master’s MISO pin. The transmission ends when the Serial Peripheral transfer data flag, SPIF, in SPSCR becomes set. At the same time that SPIF becomes set, the received Byte from the Slave is transferred to the receive data register in SPDAT. Software clears SPIF by reading the Serial Peripheral Status register (SPSCR) with the SPIF bit set, and then reading the SPDAT.

Slave Mode The SPI operates in Slave mode when the Master bit, MSTR

(2)

cleared. Before a data transmission occurs, the Slave Select pin, SS, of the Slave device must be set to’0’. SS must remain low until the transmission is complete.

In a Slave SPI Module, data enters the shift register under the control of the SCK from the Master SPI Module. After a Byte enters the shift register, it is immediately transferred to the receive data register in SPDAT, and the SPIF bit is set. To prevent an overflow condition, Slave software must then read the SPDAT before another Byte enters the shift register

(3)

. A Slave SPI must complete the write to the SPDAT (shift register) at least one bus cycle before the Master SPI starts a transmission. If the write to the data register is late, the SPI transmits the data already in the shift register from the previous transmission.

(1)

, in the SPCON register

, in the SPCON register is

Transmission Formats Software can select any of four combinations of serial clock (SCK) phase and polarity

using two bits in the SPCON: the Clock Polarity (CPOL (CPHA4). CPOL defines the default SCK line level in idle state. It has no significant effect on the transmission format. CPHA defines the edges on which the input data are sampled and the edges on which the output data are shifted (Figure 46 and Figure 47). The clock phase and polarity should be identical for the Master SPI device and the communicating Slave device.

1. The SPI Module should be configured as a Master before it is enabled (SPEN set). Also,

2. The SPI Module should be configured as a Slave before it is enabled (SPEN set).

3. The maximum frequency of the SCK for an SPI configured as a Slave is the bus clock

4. Before writing to the CPOL and CPHA bits, the SPI should be disabled (SPEN =’0’).

the Master SPI should be configured before the Slave SPI.

speed.

( 4)

) and the Clock Phase

4383D–8051–02/08

Figure 46. Data Transmission Format (CPHA = 0)

MSB bit6 bit5 bit4 bit3 bit2 bit1 LSB

bit6 bit5 bit4 bit3 bit2 bit1MSB LSB

1 32 4 5 6 7 8

Capture Point

SS (to Slave)

MISO (from Slave)

MOSI (from Master)

SCK (CPOL = 1)

SCK (CPOL = 0)

SPEN (Internal)

SCK Cycle Number

MSB bit6 bit5 bit4 bit3 bit2 bit1 LSB

bit6 bit5 bit4 bit3 bit2 bit1

MSB LSB

1 32 4 5 6 7 8

Capture Point

SS (to Slave)

MISO (from Slave)

MOSI (from Master)

SCK (CPOL = 1)

SCK (CPOL = 0)

SPEN (Internal)

SCK Cycle Number

Byte 1 Byte 2

Byte 3

MISO/MOSI

Master SS

Slave SS

(CPHA = 1)

Slave SS

(CPHA = 0)

Figure 47. Data Transmission Format (CPHA = 1)

AT89C51AC3

Figure 48. CPHA/SS Timing

As shown in Figure 46, the first SCK edge is the MSB capture strobe. Therefore, the Slave must begin driving its data before the first SCK edge, and a falling edge on the SS pin is used to start the transmission. The SS pin must be toggled high and then low between each Byte transmitted (Figure 48).

Figure 47 shows an SPI transmission in which CPHA is ’1’. In this case, the Master begins driving its MOSI pin on the first SCK edge. Therefore, the Slave uses the first SCK edge as a start transmission signal. The SS pin can remain low between transmissions (Figure 48). This format may be preferred in systems having only one Master and only one Slave driving the MISO data line.

Queuing transmission For an SPI configured in master or slave mode, a queued data byte must be transmit-

ted/received immediately after the previous transmission has completed.

4383D–8051–02/08

AT89C51AC3

When a transmission is in progress a new data can be queued and sent as soon as

MSB

B6 B5 B4 B3 B2

LSB

MOSI

SCK

MSB

B6 B5 B4 B3 B2

LSB

BYTE 1 under transmission

MSB

B6 B5 B4 B3 B2

LSB

MSB

B6 B5 B4 B3 B2

LSB

MISO

Data

Byte 1 Byte 2

Byte 3

SPTE

BYTE 2 under transmission

transmission has been completed. So it is possible to transmit bytes without latency, useful in some applications.

The SPTE bit in SPSCR is set as long as the transmission buffer is free. It means that the user application can write SPDAT with the data to be transmitted until the SPTE becomes cleared.

Figure 49 shows a queuing transmission in master mode. Once the Byte 1 is ready, it is immediately sent on the bus. Meanwhile an other byte is prepared (and the SPTE is cleared), it will be sent at the end of the current transmission. The next data must be ready before the end of the current transmission.

Figure 49. Queuing Transmission In Master Mode

In slave mode it is almost the same except it is the external master that start the transmission.

Also, in slave mode, if no new data is ready, the last value received will be the next data byte transmitted.

4383D–8051–02/08

AT89C51AC3

SCK

SS (master)

1 2 3

SCK cycle #

0 0

(slave)

(from master)

MODF detected

B6MSB

SPI enable

MODF detected

MOSI

MISO

(from master)

(from slave)

Error Conditions The following flags in the SPSCR register indicate the SPI error conditions:

Mode Fault Error (MODF) Mode Fault error in Master mode SPI indicates that the level on the Slave Select (SS)

pin is inconsistent with the actual mode of the device.

• Mode fault detection in Master mode:

MODF is set to warn that there may be a multi-master conflict for system control. In this case, the SPI system is affected in the following ways:

– An SPI receiver/error CPU interrupt request is generated

– The SPEN bit in SPCON is cleared. This disables the SPI

– The MSTR bit in SPCON is cleared

Clearing the MODF bit is accomplished by a read of SPSCR register with MODF bit set, followed by a write to the SPCON register. SPEN Control bit may be restored to its original set state after the MODF bit has been cleared.

Figure 50. Mode Fault Conditions in Master Mode (Cpha =’1’/Cpol =’0’)

4383D–8051–02/08

Note: When SS is discarded (SS disabled) it is not possible to detect a MODF error in master

mode because the SPI is internally unselected and the SS pin is a general purpose I/O.

• Mode fault detection in Slave mode

In slave mode, the MODF error is detected when SS goes high during a transmission. A transmission begins when SS goes low and ends once the incoming SCK goes back to its idle level following the shift of the eighteen data bit. A MODF error occurs if a slave is selected (SS is low) and later unselected (SS is high) even if no SCK is sent to that slave.

At any time, a ’1’ on the SS pin of a slave SPI puts the MISO pin in a high impedance state and internal state counter is cleared. Also, the slave SPI ignores all incoming SCK clocks, even if it was already in the middle of a transmission. A new transmission will be performed as soon as SS pin returns low.

AT89C51AC3

Figure 51. Mode Fault Conditions in Slave Mode

SCK

1 2 3

SCK cycle #

SS (slave)

(from master)

MODF detected

B6MSB

MODF detected

MOSI

MISO

(from master)

(from slave)

MSB

B5 B4

Note: when SS is discarded (SS disabled) it is not possible to detect a MODF error in slave

mode because the SPI is internally selected. Also the SS pin becomes a general purpose I/O.

OverRun Condition This error mean that the speed is not adapted for the running application:

An OverRun condition occurs when a byte has been received whereas the previous one has not been read by the application yet. The last byte (which generate the overrun error) does not overwrite the unread data so that it can still be read. Therefore, an overrun error always indicates the loss of data.

Interrupts Three SPI status flags can generate a CPU interrupt requests:

Table 47. SPI Interrupts

Flag Request

SPIF (SPI data transfer) SPI Transmitter Interrupt Request

MODF (Mode Fault) SPI mode-fault Interrupt Request

SPTE (Transmit register empty) SPI transmit register empty Interrupt Request

Serial Peripheral data transfer flag, SPIF: This bit is set by hardware when a transfer has been completed. SPIF bit generates transmitter CPU interrupt request only when SPTEIE is disabled.

Mode Fault flag, MODF: This bit is set to indicate that the level on the SS is inconsistent with the mode of the SPI (in both master and slave modes).

Serial Peripheral Transmit Register empty flag, SPTE: This bit is set when the transmit buffer is empty (other data can be loaded is SPDAT). SPTE bit generates transmitter CPU interrupt request only when SPTEIE is enabled.

Note: While using SPTE interruption for “burst mode” transfers (SPTEIE=’1’), the user software application should take care to clear SPTEIE, during the last but one

data reception (to be able to generate an interrupt on SPIF flag at the end of the last data reception).

4383D–8051–02/08

AT89C51AC3

SPI

CPU Interrupt Request

SPIF

SPTEIE

SPTE

MODF

MODFIE

Figure 52. SPI Interrupt Requests Generation

Registers Three registers in the SPI module provide control, status and data storage functions.

These registers are describe in the following paragraphs.

Serial Peripheral Control Register (SPCON)

• The Serial Peripheral Control Register does the following:

• Selects one of the Master clock rates

• Configure the SPI Module as Master or Slave

• Selects serial clock polarity and phase

• Enables the SPI Module

• Frees the SS pin for a general-purpose

Table 48 describes this register and explains the use of each bit

Table 48. SPCON Register

SPCON - Serial Peripheral Control Register (0D4H)

7 6 5 4 3 2 1 0

SPR2 SPEN SSDIS MSTR CPOL CPHA SPR1 SPR0

Bit Number Bit Mnemonic Description

Serial Peripheral Rate 2

7 SPR2

6 SPEN

Bit with SPR1 and SPR0 define the clock rate (See bits SPR1 and SPR0 for detail).

Serial Peripheral Enable

Cleared to disable the SPI interface (internal reset of the SPI).

Set to enable the SPI interface.

4383D–8051–02/08

5 SSDIS

4 MSTR

SS Disable

Cleared to enable SS in both Master and Slave modes.

Set to disable SS in both Master and Slave modes. In Slave mode, this bit has no effect if CPHA =’0’. When SSDIS is set, no MODF interrupt request is generated

Serial Peripheral Master

Cleared to configure the SPI as a Slave.

Set to configure the SPI as a Master.

AT89C51AC3

Bit Number Bit Mnemonic Description

Clock Polarity

3 CPOL

2 CPHA

1 SPR1

0 SPR0

Cleared to have the SCK set to ’0’ in idle state.

Set to have the SCK set to ’1’ in idle state.

Clock Phase

Cleared to have the data sampled when the SCK leaves the idle state (see CPOL).

Set to have the data sampled when the SCK returns to idle state (see CPOL).

SPR2 SPR1 SPR0 Serial Peripheral Rate

0 0 0 Invalid

0 0 1 F

0 1 0 F

0 1 1 F

1 0 0 F

1 0 1 F

1 1 0 F

1 1 1 Invalid

Reset Value = 0001 0100b

Not bit addressable

CLK PERIPH

/16

/32

/64

/128

Serial Peripheral Status Register and Control (SPSCR)

The Serial Peripheral Status Register contains flags to signal the following conditions:

• Data transfer complete

• Write collision

• Inconsistent logic level on SS pin (mode fault error)

Table 49. SPSCR Register

SPSCR - Serial Peripheral Status and Control register (0D5H)

7 6 5 4 3 2 1 0

SPIF - OVR MODF SPTE UARTM SPTEIE MODFIE

Bit

Number

7 SPIF

6 -

5 OVR

Bit

Mnemonic Description

Serial Peripheral Data Transfer Flag

Cleared by hardware to indicate data transfer is in progress or has been approved by a clearing sequence.

Set by hardware to indicate that the data transfer has been completed.

This bit is cleared when reading or writing SPDATA after reading SPSCR.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Overrun Error Flag

- Set by hardware when a byte is received whereas SPIF is set (the previous received data is not overwritten).

- Cleared by hardware when reading SPSCR

4383D–8051–02/08

AT89C51AC3

Bit

Number

4 MODF

3 SPTE

2 UARTM

1 SPTEIE

Bit

Mnemonic Description

Mode Fault

- Set by hardware to indicate that the SS pin is in inappropriate logic level (in both master and slave modes).

- Cleared by hardware when reading SPSCR

When MODF error occurred:

- In slave mode: SPI interface ignores all transmitted data while SS remains high. A new transmission is perform as soon as SS returns low.

- In master mode: SPI interface is disabled (SPEN=0, see description for SPEN bit in SPCON register).

Serial Peripheral Transmit register Empty

- Set by hardware when transmit register is empty (if needed, SPDAT can be loaded with another data).

- Cleared by hardware when transmit register is full (no more data should be loaded in SPDAT).

Serial Peripheral UART mode

Set and cleared by software:

- Clear: Normal mode, data are transmitted MSB first (default)

- Set: UART mode, data are transmitted LSB first.

Interrupt Enable for SPTE

Set and cleared by software:

- Set to enable SPTE interrupt generation (when SPTE goes high, an interrupt is generated).

- Clear to disable SPTE interrupt generation

Caution: When SPTEIE is set no interrupt generation occurred when SPIF flag goes high. To enable SPIF interrupt again, SPTEIE should be cleared.

Interrupt Enable for MODF

0 MODFIE

Set and cleared by software:

- Set to enable MODF interrupt generation

- Clear to disable MODF interrupt generation

Reset Value = 00X0 XXXXb

Not Bit addressable

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AT89C51AC3

Programmable Counter Array (PCA)

The PCA provides more timing capabilities with less CPU intervention than the standard timer/counters. Its advantages include reduced software overhead and improved accuracy. The PCA consists of a dedicated timer/counter which serves as the time base for an array of five compare/capture modules. Its clock input can be programmed to count any of the following signals:

• PCA clock frequency/6 (see “clock” section)

• PCA clock frequency/2

• Timer 0 overflow

• External input on ECI (P1.2)

Each compare/capture modules can be programmed in any one of the following modes:

• rising and/or falling edge capture,

• software timer,

• high-speed output,

• pulse width modulator.

Module 4 can also be programmed as a WatchDog timer. see the "PCA WatchDog Timer" section.

When the compare/capture modules are programmed in capture mode, software timer, or high speed output mode, an interrupt can be generated when the module executes its function. All five modules plus the PCA timer overflow share one interrupt vector.

The PCA timer/counter and compare/capture modules share Port 1 for external I/Os. These pins are listed below. If the port is not used for the PCA, it can still be used for standard I/O.

PCA Timer

PCA Component External I/O Pin

16-bit Counter P1.2/ECI

16-bit Module 0 P1.3/CEX0

16-bit Module 1 P1.4/CEX1

16-bit Module 2 P1.5/CEX2

16-bit Module 3 P1.6/CEX3

16-bit Module 4 P1.7/CEX4

The PCA timer is a common time base for all five modules (see Figure 53). The timer count source is determined from the CPS1 and CPS0 bits in the CMOD SFR (see Table

8) and can be programmed to run at:

• 1/6 the PCA clock frequency.

• 1/2 the PCA clock frequency.

• the Timer 0 overflow.

• the input on the ECI pin (P1.2).

4383D–8051–02/08

Figure 53. PCA Timer/Counter

CIDL CPS1 CPS0 ECF

CH CL

16 bit up counter

To PCA modules

FPca/6

FPca/2

T0 OVF

P1.2

Idle

CMOD 0xD9

WDTE

CF CR

CCON 0xD8

CCF4 CCF3 CCF2 CCF1 CCF0

overflow

AT89C51AC3

PCA Modules

The CMOD register includes three additional bits associated with the PCA.

• The CIDL bit which allows the PCA to stop during idle mode.

• The WDTE bit which enables or disables the WatchDog function on module 4.

• The ECF bit which when set causes an interrupt and the PCA overflow flag CF in

CCON register to be set when the PCA timer overflows.

The CCON register contains the run control bit for the PCA and the flags for the PCA timer and each module.

• The CR bit must be set to run the PCA. The PCA is shut off by clearing this bit.

• The CF bit is set when the PCA counter overflows and an interrupt will be generated

if the ECF bit in CMOD register is set. The CF bit can only be cleared by software.

• The CCF0:4 bits are the flags for the modules (CCF0 for module0...) and are set by

hardware when either a match or a capture occurs. These flags also can be cleared by software.

Each one of the five compare/capture modules has six possible functions. It can perform:

• 16-bit Capture, positive-edge triggered

• 16-bit Capture, negative-edge triggered

• 16-bit Capture, both positive and negative-edge triggered

• 16-bit Software Timer

• 16-bit High Speed Output

• 8-bit Pulse Width Modulator.

4383D–8051–02/08

In addition module 4 can be used as a WatchDog Timer.

AT89C51AC3

PCA Interrupt

CF CR

CCON

CCF4 CCF3 CCF2 CCF1 CCF0

Module 4

Module 3

Module 2

Module 1

Module 0

PCA Timer/Counter

ECCFn

CCAPMn.0

To Interrupt

IEN0.7

IEN0.6

ECF

CMOD.0

Figure 54. PCA Interrupt System

Each module in the PCA has a special function register associated with it (CCAPM0 for module 0 ...). The CCAPM0:4 registers contain the bits that control the mode that each module will operate in.

• The ECCF bit enables the CCF flag in the CCON register to generate an interrupt

when a match or compare occurs in the associated module.

• The PWM bit enables the pulse width modulation mode.

• The TOG bit when set causes the CEX output associated with the module to toggle

when there is a match between the PCA counter and the module’s capture/compare register.

• The match bit MAT when set will cause the CCFn bit in the CCON register to be set

when there is a match between the PCA counter and the module’s capture/compare register.

• The two bits CAPN and CAPP in CCAPMn register determine the edge that a

capture input will be active on. The CAPN bit enables the negative edge, and the CAPP bit enables the positive edge. If both bits are set both edges will be enabled.

• The bit ECOM in CCAPM register when set enables the comparator function.

PCA Capture Mode

To use one of the PCA modules in capture mode either one or both of the CCAPM bits CAPN and CAPP for that module must be set. The external CEX input for the module (on port 1) is sampled for a transition. When a valid transition occurs the PCA hardware loads the value of the PCA counter registers (CH and CL) into the module’s capture registers (CCAPnL and CCAPnH). If the CCFn bit for the module in the CCON SFR and the ECCFn bit in the CCAPMn SFR are set then an interrupt will be generated.

4383D–8051–02/08

Figure 55. PCA Capture Mode

CEXn n = 0, 4

PCA Counter

(8bits)

CCAPnH

CCAPnL

CCFn

CCON

PCA Interrupt Request

0CAPPn CAPNn 000 ECCFn

CCAPMn Register (n = 0, 4)

CCAPnL

(8 bits)

CCAPnH

(8 bits)

ECOMn0 0 MATn TOGn0 ECCFn

7 0

CCAPMn Register

(n = 0, 4)

(8 bits)CL(8 bits)

16-Bit Comparator

Match

Enable

CCFn

CCON reg

PCA Interrupt Request

CEXn

Compare/Capture Module

PCA Counter

“0”

“1”

Reset

Write to

CCAPnL

Write to CCAPnH

For software Timer mode, set ECOMn and MATn. For high speed output mode, set ECOMn, MATn and TOGn.

Toggle

AT89C51AC3

16-bit Software Timer Mode

The PCA modules can be used as software timers by setting both the ECOM and MAT bits in the modules CCAPMn register. The PCA timer will be compared to the module’s capture registers and when a match occurs an interrupt will occur if the CCFn (CCON SFR) and the ECCFn (CCAPMn SFR) bits for the module are both set.

Figure 56. PCA 16-bit Software Timer and High Speed Output Mode

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AT89C51AC3

High Speed Output Mode

CH CL

CCAPnH CCAPnL

ECOMn

CCAPMn, n = 0 to 4

0xDA to 0xDE

CAPNn MATn TOGn PWMn ECCFnCAPPn

16-bit comparator

Match

CF CR

CCON

0xD8

CCF4 CCF3 CCF2 CCF1 CCF0

PCA IT

Enable

CEXn

PCA counter/timer

“1”“0”

Write to

CCAPnL

Reset

Write to

CCAPnH

In this mode the CEX output (on port 1) associated with the PCA module will toggle each time a match occurs between the PCA counter and the module’s capture registers. To activate this mode the TOG, MAT, and ECOM bits in the module’s CCAPMn SFR must be set.

Figure 57. PCA High Speed Output Mode

Pulse Width Modulator Mode

All the PCA modules can be used as PWM outputs. The output frequency depends on the source for the PCA timer. All the modules will have the same output frequency because they all share the PCA timer. The duty cycle of each module is independently variable using the module’s capture register CCAPLn. When the value of the PCA CL SFR is less than the value in the module’s CCAPLn SFR the output will be low, when it is equal to or greater than it, the output will be high. When CL overflows from FF to 00, CCAPLn is reloaded with the value in CCAPHn. the allows the PWM to be updated without glitches. The PWM and ECOM bits in the module’s CCAPMn register must be set to enable the PWM mode.

4383D–8051–02/08

Figure 58. PCA PWM Mode

CL rolls over from FFh TO 00h loads CCAPnH contents into CCAPnL

CCAPnL

CCAPnH

8-Bit Comparator

CL (8 bits)

“0”

“1”

CL < CCAPnL

CL > = CCAPnL

CEX

PWMn

CCAPMn.1

ECOMn

CCAPMn.6

AT89C51AC3

PCA WatchDog Timer

An on-board WatchDog timer is available with the PCA to improve system reliability without increasing chip count. WatchDog timers are useful for systems that are sensitive to noise, power glitches, or electrostatic discharge. Module 4 is the only PCA module that can be programmed as a WatchDog. However, this module can still be used for other modes if the WatchDog is not needed. The user pre-loads a 16-bit value in the compare registers. Just like the other compare modes, this 16-bit value is compared to the PCA timer value. If a match is allowed to occur, an internal reset will be generated. This will not cause the RST pin to be driven high.

To hold off the reset, the user has three options:

• periodically change the compare value so it will never match the PCA timer,

• periodically change the PCA timer value so it will never match the compare values,

• disable the WatchDog by clearing the WDTE bit before a match occurs and then re-

enable it.

The first two options are more reliable because the WatchDog timer is never disabled as in the third option. If the program counter ever goes astray, a match will eventually occur and cause an internal reset. If other PCA modules are being used the second option not recommended either. Remember, the PCA timer is the time base for all modules; changing the time base for other modules would not be a good idea. Thus, in most applications the first solution is the best option.

4383D–8051–02/08

AT89C51AC3

PCA Registers

Table 50. CMOD Register

CMOD (S:D9h) PCA Counter Mode Register

7 6 5 4 3 2 1 0

CIDL WDTE - - - CPS1 CPS0 ECF

Bit

Number

2-1 CPS1:0

Mnemonic Description

7 CIDL

6 WDTE

5 -

4 -

3 -

0 ECF

Bit

PCA Counter Idle Control bit

Clear to let the PCA run during Idle mode. Set to stop the PCA when Idle mode is invoked.

WatchDog Timer Enable

Clear to disable WatchDog Timer function on PCA Module 4, Set to enable it.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

EWC Count Pulse Select bits

CPS1 CPS0 Clock source 0 0 Internal Clock, FPca/6 0 1 Internal Clock, FPca/2 1 0 Timer 0 overflow 1 1 External clock at ECI/P1.2 pin (Max. Rate = FPca/4)

Enable PCA Counter Overflow Interrupt bit

Clear to disable CF bit in CCON register to generate an interrupt. Set to enable CF bit in CCON register to generate an interrupt.

100

Reset Value = 00XX X000b

4383D–8051–02/08

ATMEL AT89C51AC3 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Features

Description

Block Diagram

Pin Configuration

I/O Configurations

Port 1, Port 3 and Port 4

Port 0 and Port 2

Read-Modify-Write Instructions

Quasi-Bidirectional Port Operation

SFR Mapping

Clock

Description

Registers

Data Memory

Internal Space

External Space

Dual Data Pointer

Registers

Power Monitor

Description

Reset

Introduction

Reset Input

Reset Output

Power Management

Introduction

Idle Mode

Power-Down Mode

Registers

EEPROM Data Memory

Write Data in the Column Latches

Programming

Read Data

Examples

Registers

External Code Memory Access

Flash Memory Architecture

Overview of FM0 Operations

Operation Cross Memory Access

Sharing Instructions

Flash Programming and Erasure

Boot Process

Application Programming Interface

XROW Bytes

Hardware Security Byte

Serial I/O Port

Framing Error Detection

Automatic Address Recognition

Given Address

Broadcast Address

Registers

Timers/Counters

Timer/Counter Operations

Timer 0

Timer 1

Interrupt

Registers

Timer 2

Auto-Reload Mode

Registers

Watchdog Timer

Watchdog Programming

Watchdog Timer During Power-down Mode and Idle

Serial Port Interface (SPI)

Features

Signal Description

Functional Description

Programmable Counter Array (PCA)

PCA Timer

PCA Modules

PCA Interrupt

PCA Capture Mode

16-bit Software Timer Mode

High Speed Output Mode

Pulse Width Modulator Mode

PCA WatchDog Timer