Philips P80C31SFBB, P87C51UFAA, P87C51UBAA, P87C51SFPN, P87C51SFBB Datasheet

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80C51/87C51/80C31

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless low voltage (2.7V–5.5V),

low power, high speed (33 MHz)

Product specification

Supersedes data of 1999 Apr 01

IC28 Data Handbook

2000 Jan 20

INTEGRATED CIRCUITS

Philips Semiconductors Product specification

80C51/87C51/80C31

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless, low voltage (2.7V–5.5V),

low power, high speed (33 MHz)

2000 Jan 20 853–0169 23001

DESCRIPTION

The Philips 8XC51/31 is a high-performance static 80C51 design

fabricated with Philips high-density CMOS technology with operation

from 2.7V to 5.5V .

The 8XC51/31 contains a 4k × 8 ROM, a 128 × 8 RAM, 32 I/O lines,

three 16-bit counter/timers, a six-source, four-priority level nested

interrupt structure, a serial I/O port for either multi-processor

communications, I/O expansion or full duplex UART, and on-chip

oscillator and clock circuits.

In addition, the device is a low power static design which offers a

wide range of operating frequencies down to zero. Two software

selectable modes of power reduction—idle mode and power-down

mode are available. The idle mode freezes the CPU while allowing

the RAM, timers, serial port, and interrupt system to continue

functioning. The power-down mode saves the RAM contents but

freezes the oscillator, causing all other chip functions to be

inoperative. Since the design is static, the clock can be stopped

without loss of user data and then the execution resumed from the

point the clock was stopped.

SELECTION TABLE

For applications requiring more ROM and RAM,

see the 8XC52/54/58/80C32, 8XC51FA/FB/FC/80C51FA,

and 8XC51RA+/RB+/RC+/80C51RA+ data sheet.

ROM/EPROM

Memory Size

(X by 8)

RAM Size

(X by 8)

Programmable

Timer Counter

(PCA)

Hardware

Watch Dog

Timer

80C31/8XC51

0K/4K 128 No No

80C32/8XC52/54/58

0K/8K/16K/32K 256 No No

80C51FA/8XC51FA/FB/FC

0K/8K/16K/32K 256 Yes No

80C51RA+/8XC51RA+/RB+/RC+

0K/8K/16K/32K 512 Yes Yes

8XC51RD+

64K 1024 Yes Yes

FEA TURES

•8051 Central Processing Unit

– 4k × 8 ROM (80C51)

– 128 × 8 RAM

– Three 16-bit counter/timers

– Boolean processor

– Full static operation

– Low voltage (2.7V to 5.5V@ 16MHz) operation

•Memory addressing capability

– 64k ROM and 64k RAM

•Power control modes:

– Clock can be stopped and resumed

– Idle mode

– Power-down mode

•CMOS and TTL compatible

•TWO speed ranges at V

= 5V

– 0 to 16MHz

– 0 to 33MHz

•Three package styles

•Extended temperature ranges

•Dual Data Pointers

•Security bits:

– ROM (2 bits)

– OTP/EPROM (3 bits)

•Encryption array—64 bytes

•4 level priority interrupt

•6 interrupt sources

•Four 8-bit I/O ports

•Full–duplex enhanced UART

– Framing error detection

– Automatic address recognition

•Programmable clock out

•Asynchronous port reset

•Low EMI (inhibit ALE)

•Wake-up from Power Down by an external interrupt (8XC51)

Philips Semiconductors Product specification

80C51/87C51/80C31

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless, low voltage (2.7V–5.5V),

low power, high speed (33 MHz)

2000 Jan 20

80C51/87C51 AND 80C31 ORDERING INFORMATION

MEMORY SIZE

4K × 8

ROMless

TEMPERATURE RANGE °C

AND PACKAGE

VOLTAGE

RANGE

FREQ.

(MHz)

DWG.

ROM P80C51SBPN

OTP P87C51SBPN

P80C31SBPN

Plastic

line

Package

SOT129

ROM P80C51SBAA

OTP P87C51SBAA

P80C31SBAA

Plastic

Leaded

Chip

Carrier

SOT187

ROM P80C51SBBB

OTP P87C51SBBB

P80C31SBBB

Plastic

Flat

Pack

SOT307

ROM P80C51SFPN

OTP P87C51SFPN

P80C31SFPN

–

Plastic

line

Package

SOT129

ROM P80C51SFAA

OTP P87C51SFAA

P80C31SFAA

–

Plastic

Leaded

Chip

Carrier

SOT187

ROM P80C51SFBB

OTP P87C51SFBB

P80C31SFBB

–

Plastic

Flat

Pack

SOT307

ROM P80C51UBAA

OTP P87C51UBAA

P80C31UBAA

Plastic

Leaded

Chip

Carrier

SOT187

ROM P80C51UBPN

OTP P87C51UBPN

P80C31UBPN

Plastic

line

Package

SOT129

ROM P80C51UBBB

OTP P87C51UBBB

P80C31UBBB

Plastic

Flat

Pack

SOT307

ROM P80C51UFAA

OTP P87C51UFAA

P80C31UFAA

–

Plastic

Leaded

Chip

Carrier

SOT187

ROM P80C51UFPN

OTP P87C51UFPN

P80C31UFPN

–

Plastic

line

Package

SOT129

ROM P80C51UFBB

OTP P87C51UFBB

P80C31UFBB

–

Plastic

Flat

Pack

SOT307

80C51/87C51 AND 80C31 ORDERING INFORMATION

DEVICE NUMBER (P87C51) OPERATING FREQUENCY, MAX (S) TEMPERATURE RANGE (B) PACKAGE (AA)

P80C51 ROM S = 16 MHz

B = 0_ to +70_C

AA = PLCC

P87C51 OTP U = 33 MHz

F = –40_C to +85_C

BB = PQFP

P80C31 ROMless PN = PDIP

Philips Semiconductors Product specification

80C51/87C51/80C31

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless, low voltage (2.7V–5.5V),

low power, high speed (33 MHz)

2000 Jan 20

BLOCK DIAGRAM

SU00845

PSEN

EAV

ALE/PROG

RST

XTAL1 XTAL2

PORT 0

DRIVERS

PORT 2

DRIVERS

RAM ADDR

RAM

PORT 0

LATCH

PORT 2

LATCH

ROM/EPROM

ACC

STACK

POINTER

TMP2

TMP1

ALU

TIMING

AND

CONTROL

INSTRUCTION

OSCILLATOR

PSW

PORT 1

LATCH

PORT 3

LATCH

PORT 1

DRIVERS

PORT 3

DRIVERS

PROGRAM

ADDRESS

BUFFER

INCRE-

MENTER

PROGRAM

COUNTER

DPTR’S

MULTIPLE

P1.0–P1.7

P3.0–P3.7

P0.0–P0.7 P2.0–P2.7

SFRs

TIMERS

8 16

Philips Semiconductors Product specification

80C51/87C51/80C31

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless, low voltage (2.7V–5.5V),

low power, high speed (33 MHz)

2000 Jan 20

LOGIC SYMBOL

PORT 0

PORT 1PORT 2

PORT 3

ADDRESS AND

DATA BUS

ADDRESS BUS

T2EX

RxD

TxD

INT0

INT1

SECONDARY FUNCTIONS

RST

EA/V

PSEN

ALE/PROG

XTAL1

XTAL2

SU00830

PIN CONFIGURA TIONS

SU01063

T2/P1.0

T2EX/P1.1

P1.2

P1.3

P1.4

P1.5

P1.6

RST

RxD/P3.0

TxD/P3.1

INT0

/P3.2

INT1

/P3.3

T0/P3.4

T1/P3.5

P1.7

/P3.6

/P3.7

XTAL2

XTAL1

P2.0/A8

P2.1/A9

P2.2/A10

P2.3/A11

P2.4/A12

P2.5/A13

P2.6/A14

P2.7/A15

PSEN

ALE

P0.7/AD7

P0.6/AD6

P0.5/AD5

P0.4/AD4

P0.3/AD3

P0.2/AD2

P0.1/AD1

P0.0/AD0

DUAL

IN-LINE

PACKAGE

PLASTIC LEADED CHIP CARRIER PIN FUNCTIONS

SU01062

LCC

6140

18 28

Pin Function

1 NIC*

2 P1.0/T2

3 P1.1/T2EX

4 P1.2

5 P1.3

6 P1.4

7 P1.5

8 P1.6

9 P1.7

10 RST

11 P3.0/RxD

12 NIC*

13 P3.1/TxD

14 P3.2/INT0

15 P3.3/INT1

Pin Function

16 P3.4/T0

17 P3.5/T1

18 P3.6/WR

19 P3.7/RD

20 XTAL2

21 XTAL1

22 V

23 NIC*

24 P2.0/A8

25 P2.1/A9

26 P2.2/A10

27 P2.3/A11

28 P2.4/A12

29 P2.5/A13

30 P2.6/A14

Pin Function

31 P2.7/A15

32 PSEN

33 ALE

34 NIC*

35 EA/V

36 P0.7/AD7

37 P0.6/AD6

38 P0.5/AD5

39 P0.4/AD4

40 P0.3/AD3

41 P0.2/AD2

42 P0.1/AD1

43 P0.0/AD0

44 V

* NO INTERNAL CONNECTION

PLASTIC QUAD FLAT PACK

PIN FUNCTIONS

SU01064

PQFP

44 34

12 22

Pin Function

1 P1.5

2 P1.6

3 P1.7

4 RST

5 P3.0/RxD

6 NIC*

7 P3.1/TxD

8 P3.2/INT0

9 P3.3/INT1

10 P3.4/T0

11 P3.5/T1

12 P3.6/WR

13 P3.7/RD

14 XTAL2

15 XTAL1

Pin Function

16 V

17 NIC*

18 P2.0/A8

19 P2.1/A9

20 P2.2/A10

21 P2.3/A11

22 P2.4/A12

23 P2.5/A13

24 P2.6/A14

25 P2.7/A15

26 PSEN

27 ALE

28 NIC*

29 EA

30 P0.7/AD7

Pin Function

31 P0.6/AD6

32 P0.5/AD5

33 P0.4/AD4

34 P0.3/AD3

35 P0.2/AD2

36 P0.1/AD1

37 P0.0/AD0

38 V

39 NIC*

40 P1.0/T2

41 P1.1/T2EX

42 P1.2

43 P1.3

44 P1.4

* NO INTERNAL CONNECTION

Philips Semiconductors Product specification

80C51/87C51/80C31

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless, low voltage (2.7V–5.5V),

low power, high speed (33 MHz)

2000 Jan 20

PIN DESCRIPTIONS

PIN NUMBER

MNEMONIC DIP LCC QFP TYPE NAME AND FUNCTION

20 22 16 I Ground: 0V reference.

40 44 38 I Power Supply: This is the power supply voltage for normal, idle, and power-down operation.

P0.0–0.7 39–32 43–36 37–30 I/O Port 0: Port 0 is an open-drain, bidirectional I/O port. Port 0 pins that have 1s written to

them float and can be used as high-impedance inputs. Port 0 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 1s. Port 0 also outputs the

code bytes during program verification and received code bytes during EPROM

programming. External pull-ups are required during program verification.

P1.0–P1.7 1–8 2–9 40–44,

1–3

I/O Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. Port 1 pins that have 1s

written to them are pulled high by the internal pull-ups and can be used as inputs. As inputs,

port 1 pins that are externally pulled low will source current because of the internal pull-ups.

(See DC Electrical Characteristics: I

). Port 1 also receives the low-order address byte

during program memory verification. Alternate functions for Port 1 include:

1 2 40 I/O T2 (P1.0): Timer/Counter 2 external count input/clockout (see Programmable Clock-Out).

2 3 41 I T2EX (P1.1): Timer/Counter 2 Reload/Capture/Direction control.

P2.0–P2.7 21–28 24–31 18–25 I/O Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. Port 2 pins that have 1s

written to them are pulled high by the internal pull-ups and can be used as inputs. As inputs,

port 2 pins that are externally being pulled low will source current because of the internal

pull-ups. (See DC Electrical Characteristics: I

). Port 2 emits the high-order address byte

during fetches from external program memory and during accesses to external data memory

that use 16-bit addresses (MOVX @DPTR). In this application, it uses strong internal

pull-ups when emitting 1s. During accesses to external data memory that use 8-bit addresses

(MOV @Ri), port 2 emits the contents of the P2 special function register. Some Port 2 pins

receive the high order address bits during EPROM programming and verification.

P3.0–P3.7 10–17 11,

13–19

7–13

I/O Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. Port 3 pins that have 1s

written to them are pulled high by the internal pull-ups and can be used as inputs. As inputs,

port 3 pins that are externally being pulled low will source current because of the pull-ups.

(See DC Electrical Characteristics: I

). Port 3 also serves the special features of the 80C51

family, as listed below:

10 11 5 I RxD (P3.0): Serial input port

11 13 7 O TxD (P3.1): Serial output port

12 14 8 I INT0 (P3.2): External interrupt

13 15 9 I INT1 (P3.3): External interrupt

14 16 10 I T0 (P3.4): Timer 0 external input

15 17 11 I T1 (P3.5): Timer 1 external input

16 18 12 O WR (P3.6): External data memory write strobe

17 19 13 O RD (P3.7): External data memory read strobe

RST 9 10 4 I Reset: A high on this pin for two machine cycles while the oscillator is running, resets the

device. An internal diffused resistor to V

permits a power-on reset using only an external

capacitor to V

ALE/PROG 30 33 27 O Address Latch Enable/Program Pulse: Output pulse for latching the low byte of the

address during an access to external memory. In normal operation, ALE is emitted at a

constant rate of 1/6 the oscillator frequency, and can be used for external timing or clocking.

Note that one ALE pulse is skipped during each access to external data memory. This pin is

also the program pulse input (PROG

) during EPROM programming. ALE can be disabled by

setting SFR auxiliary.0. With this bit set, ALE will be active only during a MOVX instruction.

PSEN 29 32 26 O Program Store Enable: The read strobe to external program memory. When the 8XC51/31

is executing code from the external program memory, PSEN is activated twice each

machine cycle, except that two PSEN activations are skipped during each access to

external data memory. PSEN is not activated during fetches from internal program memory.

EA/V

31 35 29 I External Access Enable/Programming Supply Voltage: EA must be externally held low

to enable the device to fetch code from external program memory locations 0000H and

0FFFH. If EA

is held high, the device executes from internal program memory unless the

program counter contains an address greater than 0FFFH. This pin also receives the

12.75V programming supply voltage (V

) during EPROM programming. If security bit 1 is

programmed, EA will be internally latched on Reset.

XTAL1 19 21 15 I Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock generator

circuits.

XTAL2 18 20 14 O Crystal 2: Output from the inverting oscillator amplifier.

NOTE:

To avoid “latch-up” effect at power-on, the voltage on any pin at any time must not be higher than V

+ 0.5V or V

– 0.5V, respectively.

Philips Semiconductors Product specification

80C51/87C51/80C31

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless, low voltage (2.7V–5.5V),

low power, high speed (33 MHz)

2000 Jan 20

Table 1. 8XC51/80C31 Special Function Registers

SYMBOL DESCRIPTION

DIRECT

ADDRESS

BIT ADDRESS, SYMBOL, OR ALTERNATIVE PORT FUNCTION

MSB LSB

RESET

VALUE

ACC* Accumulator E0H E7 E6 E5 E4 E3 E2 E1 E0 00H

AUXR# Auxiliary 8EH – – – – – – – AO xxxxxxx0B

AUXR1# Auxiliary 1 A2H – – – LPEP

WUPD

0 – DPS xxx000x0B

B* B register F0H F7 F6 F5 F4 F3 F2 F1 F0 00H

DPTR: Data Pointer (2 bytes)

DPH Data Pointer High 83H 00H

DPL Data Pointer Low 82H 00H

AF AE AD AC AB AA A9 A8

IE* Interrupt Enable A8H EA – ET2 ES ET1 EX1 ET0 EX0 0x000000B

BF BE BD BC BB BA B9 B8

IP* Interrupt Priority B8H – – PT2 PS PT1 PX1 PT0 PX0 xx000000B

B7 B6 B5 B4 B3 B2 B1 B0

IPH# Interrupt Priority High B7H – – PT2H PSH PT1H PX1H PT0H PX0H xx000000B

87 86 85 84 83 82 81 80

P0* Port 0 80H AD7 AD6 AD5 AD4 AD3 AD2 AD1 AD0 FFH

97 96 95 94 93 92 91 90

P1* Port 1 90H – – – – – – T2EX T2 FFH

A7 A6 A5 A4 A3 A2 A1 A0

P2* Port 2 A0H AD15 AD14 AD13 AD12 AD11 AD10 AD9 AD8 FFH

B7 B6 B5 B4 B3 B2 B1 B0

P3* Port 3 B0H RD WR T1 T0 INT1 INT0 TxD RxD FFH

PCON#

Power Control 87H SMOD1 SMOD0 – POF GF1 GF0 PD IDL 00xx0000B

D7 D6 D5 D4 D3 D2 D1 D0

PSW* Program Status Word D0H CY AC F0 RS1 RS0 OV – P 000000x0B

RACAP2H# Timer 2 Capture High CBH 00H

RACAP2L# Timer 2 Capture Low CAH 00H

SADDR# Slave Address A9H 00H

SADEN# Slave Address Mask B9H 00H

SBUF Serial Data Buffer 99H xxxxxxxxB

9F 9E 9D 9C 9B 9A 99 98

SCON* Serial Control 98H

SM0/FE

SM1 SM2 REN TB8 RB8 TI RI 00H

SP Stack Pointer 81H 07H

8F 8E 8D 8C 8B 8A 89 88

TCON* Timer Control 88H TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0 00H

CF CE CD CC CB CA C9 C8

T2CON* Timer 2 Control C8H TF2 EXF2 RCLK TCLK EXEN2 TR2 C/T2 CP/RL2 00H

T2MOD# Timer 2 Mode Control C9H – – – – – – T2OE DCEN xxxxxx00B

TH0 Timer High 0 8CH 00H

TH1 Timer High 1 8DH 00H

TH2# Timer High 2 CDH 00H

TL0 Timer Low 0 8AH 00H

TL1 Timer Low 1 8BH 00H

TL2# Timer Low 2 CCH 00H

TMOD Timer Mode 89H GA TE C/T M1 M0 GATE C/T M1 M0 00H

* SFRs are bit addressable.

# SFRs are modified from or added to the 80C51 SFRs.

– Reserved bits.

1. Reset value depends on reset source.

2. LPEP – Low Power EPROM operation (OTP/EPROM only)

3. Not available on 80C31.

Philips Semiconductors Product specification

80C51/87C51/80C31

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless, low voltage (2.7V–5.5V),

low power, high speed (33 MHz)

2000 Jan 20

OSCILLA T OR CHARACTERISTICS

XTAL1 and XTAL2 are the input and output, respectively, of an

inverting amplifier . The pins can be configured for use as an on-chip

oscillator, as shown in the logic symbol.

To drive the device from an external clock source, XTAL1 should be

driven while XTAL2 is left unconnected. There are no requirements

on the duty cycle of the external clock signal, because the input to

the internal clock circuitry is through a divide-by-two flip-flop.

However, minimum and maximum high and low times specified in

the data sheet must be observed.

Reset

A reset is accomplished by holding the RST pin high for at least two

machine cycles (24 oscillator periods), while the oscillator is running.

To insure a good power-up reset, the RST pin must be high long

enough to allow the oscillator time to start up (normally a few

milliseconds) plus two machine cycles.

Stop Clock Mode

The static design enables the clock speed to be reduced down to

0 MHz (stopped). When the oscillator is stopped, the RAM and

Special Function Registers retain their values. This mode allows

step-by-step utilization and permits reduced system power

consumption by lowering the clock frequency down to any value. For

lowest power consumption the Power Down mode is suggested.

Idle Mode

In idle mode (see Table 2), the CPU puts itself to sleep while all of

the on-chip peripherals stay active. The instruction to invoke the idle

mode is the last instruction executed in the normal operating mode

before the idle mode is activated. The CPU contents, the on-chip

RAM, and all of the special function registers remain intact during

this mode. The idle mode can be terminated either by any enabled

interrupt (at which time the process is picked up at the interrupt

service routine and continued), or by a hardware reset which starts

the processor in the same manner as a power-on reset.

Power-Down Mode

To save even more power, a Power Down mode (see Table 2) can

be invoked by software. In this mode, the oscillator is stopped and

the instruction that invoked Power Down is the last instruction

executed. The on-chip RAM and Special Function Registers retain

their values down to 2.0V and care must be taken to return V

the minimum specified operating voltages before the Power Down

Mode is terminated.

For the 87C51 and 80C51 either a hardware reset or external

interrupt can be used to exit from Power Down. Reset redefines all

the SFRs but does not change the on-chip RAM. An external

interrupt allows both the SFRs and the on-chip RAM to retain their

values. WUPD (AUXR1.3–Wakeup from Power Down) enables or

disables the wakeup from power down with external interrupt.

Where:

WUPD = 0 Disable

WUPD = 1 Enable

To properly terminate Power Down the reset or external interrupt

should not be executed before V

is restored to its normal

operating level and must be held active long enough for the

oscillator to restart and stabilize (normally less than 10ms).

With an external interrupt, INT0 or INT1 must be enabled and

configured as level-sensitive. Holding the pin low restarts the

oscillator but bringing the pin back high completes the exit. Once the

interrupt is serviced, the next instruction to be executed after RETI

will be the one following the instruction that put the device into

Power Down.

For the 80C31, wakeup from power down is always enabled.

LPEP

The eprom array contains some analog circuits that are not required

when V

is less than 4V, but are required for a V

greater than

4V. The LPEP bit (AUXR.4), when set, will powerdown these analog

circuits resulting in a reduced supply current. This bit should be set

ONLY for applications that operate at a V

less tan 4V.

Design Consideration

•When the idle mode is terminated by a hardware reset, the device

normally resumes program execution, from where it left off, up to

two machine cycles before the internal reset algorithm takes

control. On-chip hardware inhibits access to internal RAM in this

event, but access to the port pins is not inhibited. To eliminate the

possibility of an unexpected write when Idle is terminated by reset,

the instruction following the one that invokes Idle should not be

one that writes to a port pin or to external memory.

ONCE Mode

The ONCE (“On-Circuit Emulation”) Mode facilitates testing and

debugging of systems without the device having to be removed from

the circuit. The ONCE Mode is invoked by:

1. Pull ALE low while the device is in reset and PSEN

is high;

2. Hold ALE low as RST is deactivated.

While the device is in ONCE Mode, the Port 0 pins go into a float

state, and the other port pins and ALE and PSEN

are weakly pulled

high. The oscillator circuit remains active. While the 8XC51/31 is in

this mode, an emulator or test CPU can be used to drive the circuit.

Normal operation is restored when a normal reset is applied.

Table 2. External Pin Status During Idle and Power-Down Modes

MODE PROGRAM MEMORY ALE PSEN PORT 0 PORT 1 PORT 2 PORT 3

Idle Internal 1 1 Data Data Data Data

Idle External 1 1 Float Data Address Data

Power-down Internal 0 0 Data Data Data Data

Power-down External 0 0 Float Data Data Data

Philips Semiconductors Product specification

80C51/87C51/80C31

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless, low voltage (2.7V–5.5V),

low power, high speed (33 MHz)

2000 Jan 20

Programmable Clock-Out

A 50% duty cycle clock can be programmed to come out on P1.0.

This pin, besides being a regular I/O pin, has two alternate

functions. It can be programmed:

1. to input the external clock for Timer/Counter 2, or

2. to output a 50% duty cycle clock ranging from 61Hz to 4MHz at a

16MHz operating frequency.

To configure the Timer/Counter 2 as a clock generator, bit C/T2 (in

T2CON) must be cleared and bit T20E in T2MOD must be set. Bit

TR2 (T2CON.2) also must be set to start the timer.

The Clock-Out frequency depends on the oscillator frequency and

the reload value of Timer 2 capture registers (RCAP2H, RCAP2L)

as shown in this equation:

Oscillator Frequency

4 (65536 * RCAP2H, RCAP2L)

Where:

(RCAP2H,RCAP2L) = the content of RCAP2H and RCAP2L

taken as a 16-bit unsigned integer.

In the Clock-Out mode Timer 2 roll-overs will not generate an

interrupt. This is similar to when it is used as a baud-rate generator.

It is possible to use Timer 2 as a baud-rate generator and a clock

generator simultaneously. Note, however, that the baud-rate and the

Clock-Out frequency will be the same.

TIMER 2 OPERATION

Timer 2

Timer 2 is a 16-bit Timer/Counter which can operate as either an

event timer or an event counter, as selected by C/T

2* in the special

function register T2CON (see Figure 1). Timer 2 has three operating

modes:Capture, Auto-reload (up or down counting) ,and Baud Rate

Generator, which are selected by bits in the T2CON as shown in

Table 3.

Capture Mode

In the capture mode there are two options which are selected by bit

EXEN2 in T2CON. If EXEN2=0, then timer 2 is a 16-bit timer or

counter (as selected by C/T2* in T2CON) which, upon overflowing

sets bit TF2, the timer 2 overflow bit. This bit can be used to

generate an interrupt (by enabling the Timer 2 interrupt bit in the

IE register). If EXEN2= 1, Timer 2 operates as described above, but

with the added feature that a 1- to -0 transition at external input

T2EX causes the current value in the Timer 2 registers, TL2 and

TH2, to be captured into registers RCAP2L and RCAP2H,

respectively. In addition, the transition at T2EX causes bit EXF2 in

T2CON to be set, and EXF2 like TF2 can generate an interrupt

(which vectors to the same location as Timer 2 overflow interrupt.

The Timer 2 interrupt service routine can interrogate TF2 and EXF2

to determine which event caused the interrupt). The capture mode is

illustrated in Figure 2 (There is no reload value for TL2 and TH2 in

this mode. Even when a capture event occurs from T2EX, the

counter keeps on counting T2EX pin transitions or osc/12 pulses.).

Auto-Reload Mode (Up or Down Counter)

In the 16-bit auto-reload mode, Timer 2 can be configured (as either

a timer or counter (C/T2* in T2CON)) then programmed to count up

or down. The counting direction is determined by bit DCEN(Down

Counter Enable) which is located in the T2MOD register (see

Figure 3). When reset is applied the DCEN=0 which means Timer 2

will default to counting up. If DCEN bit is set, Timer 2 can count up

or down depending on the value of the T2EX pin.

Figure 4 shows Timer 2 which will count up automatically since

DCEN=0. In this mode there are two options selected by bit EXEN2

in T2CON register. If EXEN2=0, then T imer 2 counts up to 0FFFFH

and sets the TF2 (Overflow Flag) bit upon overflow. This causes the

Timer 2 registers to be reloaded with the 16-bit value in RCAP2L

and RCAP2H. The values in RCAP2L and RCAP2H are preset by

software means.

If EXEN2=1, then a 16-bit reload can be triggered either by an

overflow or by a 1-to-0 transition at input T2EX. This transition also

sets the EXF2 bit. The Timer 2 interrupt, if enabled, can be

generated when either TF2 or EXF2 are 1.

In Figure 5 DCEN=1 which enables Timer 2 to count up or down.

This mode allows pin T2EX to control the direction of count. When a

logic 1 is applied at pin T2EX Timer 2 will count up. Timer 2 will

overflow at 0FFFFH and set the TF2 flag, which can then generate

an interrupt, if the interrupt is enabled. This timer overflow also

causes the 16–bit value in RCAP2L and RCAP2H to be reloaded

into the timer registers TL2 and TH2.

When a logic 0 is applied at pin T2EX this causes Timer 2 to count

down. The timer will underflow when TL2 and TH2 become equal to

the value stored in RCAP2L and RCAP2H. Timer 2 underflow sets

the TF2 flag and causes 0FFFFH to be reloaded into the timer

registers TL2 and TH2.

The external flag EXF2 toggles when Timer 2 underflows or

overflows. This EXF2 bit can be used as a 17th bit of resolution if

needed. The EXF2 flag does not generate an interrupt in this mode

of operation.

Table 3. Timer 2 Operating Modes

RCLK + TCLK CP/RL2 TR2 MODE

0 0 1 16-bit Auto-reload

0 1 1 16-bit Capture

1 X 1 Baud rate generator

X X 0 (off)

Philips Semiconductors Product specification

80C51/87C51/80C31

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless, low voltage (2.7V–5.5V),

low power, high speed (33 MHz)

2000 Jan 20

(MSB) (LSB)

Symbol Position Name and Significance

TF2 T2CON.7 Timer 2 overflow flag set by a Timer 2 overflow and must be cleared by software. TF2 will not be set

when either RCLK or TCLK = 1.

EXF2 T2CON.6 Timer 2 external flag set when either a capture or reload is caused by a negative transition on T2EX and

EXEN2 = 1. When Timer 2 interrupt is enabled, EXF2 = 1 will cause the CPU to vector to the Timer 2

interrupt routine. EXF2 must be cleared by software. EXF2 does not cause an interrupt in up/down

counter mode (DCEN = 1).

RCLK T2CON.5 Receive clock flag. When set, causes the serial port to use Timer 2 overflow pulses for its receive clock

in modes 1 and 3. RCLK = 0 causes Timer 1 overflow to be used for the receive clock.

TCLK T2CON.4 Transmit clock flag. When set, causes the serial port to use Timer 2 overflow pulses for its transmit clock

in modes 1 and 3. TCLK = 0 causes Timer 1 overflows to be used for the transmit clock.

EXEN2 T2CON.3 Timer 2 external enable flag. When set, allows a capture or reload to occur as a result of a negative

transition on T2EX if Timer 2 is not being used to clock the serial port. EXEN2 = 0 causes Timer 2 to

ignore events at T2EX.

TR2 T2CON.2 Start/stop control for Timer 2. A logic 1 starts the timer.

C/T2

T2CON.1 Timer or counter select. (Timer 2)

0 = Internal timer (OSC/12)

1 = External event counter (falling edge triggered).

CP/RL2

T2CON.0 Capture/Reload flag. When set, captures will occur on negative transitions at T2EX if EXEN2 = 1. When

cleared, auto-reloads will occur either with Timer 2 overflows or negative transitions at T2EX when

EXEN2 = 1. When either RCLK = 1 or TCLK = 1, this bit is ignored and the timer is forced to auto-reload

on Timer 2 overflow .

TF2 EXF2 RCLK TCLK EXEN2 TR2 C/T2

CP/RL2

SU00728

Figure 1. Timer/Counter 2 (T2CON) Control Register

OSC

÷ 12

C/T2 = 0

C/T2

= 1

TR2

Control

TL2

(8-bits)

TH2

(8-bits)

TF2

RCAP2L RCAP2H

EXEN2

Control

EXF2

Timer 2

Interrupt

T2EX Pin

Transition

Detector

T2 Pin

Capture

SU00066

Figure 2. Timer 2 in Capture Mode

Philips Semiconductors Product specification

80C51/87C51/80C31

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless, low voltage (2.7V–5.5V),

low power, high speed (33 MHz)

2000 Jan 20

Not Bit Addressable

Symbol Function

— Not implemented, reserved for future use.*

T2OE Timer 2 Output Enable bit.

DCEN Down Count Enable bit. When set, this allows Timer 2 to be configured as an up/down counter.

— — — — — — T2OE DCEN

SU00729

76543210

* User software should not write 1s to reserved bits. These bits may be used in future 8051 family products to invoke new features.

In that case, the reset or inactive value of the new bit will be 0, and its active value will be 1. The value read from a reserved bit is

indeterminate.

Bit

T2MOD Address = 0C9H Reset Value = XXXX XX00B

Figure 3. Timer 2 Mode (T2MOD) Control Register

OSC

÷ 12

C/T2 = 0

C/T2

= 1

TR2

CONTROL

TL2

(8-BITS)

TH2

(8-BITS)

TF2

RCAP2L RCAP2H

EXEN2

CONTROL

EXF2

TIMER 2

INTERRUPT

T2EX PIN

TRANSITION

DETECTOR

T2 PIN

RELOAD

SU00067

Figure 4. Timer 2 in Auto-Reload Mode (DCEN = 0)

Philips Semiconductors Product specification

80C51/87C51/80C31

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless, low voltage (2.7V–5.5V),

low power, high speed (33 MHz)

2000 Jan 20

÷12

C/T2 = 0

C/T2

= 1

TL2 TH2

TR2

CONTROL

T2 PIN

SU00730

FFH FFH

RCAP2L RCAP2H

(UP COUNTING RELOAD VALUE) T2EX PIN

TF2

INTERRUPT

COUNT

DIRECTION

1 = UP

0 = DOWN

EXF2

OVERFLOW

(DOWN COUNTING RELOAD VALUE)

TOGGLE

OSC

Figure 5. Timer 2 Auto Reload Mode (DCEN = 1)

OSC

÷ 2

C/T2 = 0

C/T2

= 1

TR2

Control

TL2

(8-bits)

TH2

(8-bits)

÷ 16

RCAP2L RCAP2H

EXEN2

Control

EXF2

Timer 2

Interrupt

T2EX Pin

Transition

Detector

T2 Pin

Reload

NOTE: OSC. Freq. is divided by 2, not 12.

÷ 2

“0” “1”

RX Clock

÷ 16 TX Clock

“0”“1”

Timer 1

Overflow

Note availability of additional external interrupt.

SMOD

RCLK

TCLK

SU00068

Figure 6. Timer 2 in Baud Rate Generator Mode

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