2001 Apr 06

8

Philips Semiconductors

Preliminary specification

P87C51MB2/P87C51MC2

80C51 8-bit microcontroller family with extended memory

64KB/96KB OTP with 2KB/3KB RAM

P4.0 - P4.1

12,34

I/O

Port 4: Port 4 is an 8-bit bidirectional I/O port with internal pull-ups on all pin. Port 4 pins

that have 1s written to them are pulled high by the internal pull-ups and can be used as

inputs. As inputs, port 4 pins that are externally pulled low will source current because of

the internal pull-ups. (Note: When SFR bit SPEN (SPCTL.6) is ’1’, the pull-ups at these port

pins are disabled.)

12

I

P4.0

RXD1

Serial input port 1. (Note: This pin is a no connect pin on some

derivatives.) (with pull-up on pin)

I/O

MISO

SPI Master In/Slave Out (Selected when SFR bit SPEN (SPCTL.6)

is ’1’, in which case the pull-up for this pin is disabled)

34

O

P4.1

TXD1

Serial output port 1. (Note: This pin is a no connect pin on some

derivatives.) (with pull-up on pin)

I

SS

SPI Slave Select (Selected when SFR bit SPEN (SPCTL.6) is ’1’,

in which case the pull-up for this pin is disabled)

RST

10

I

Reset: A high on this pin for two machine cycles while the oscillator is running, resets the

ALE

33

O

Address Latch Enable: 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. If SFR bit AO (AUXR.0) is

’0’, ALE is emitted at the constant rate as indicated above. With this bit set to ’1’, ALE will

be active only during a MOVX instruction.

PSEN

32

O

Program Store Enable: The read strobe to external program memory. When executing

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

except that two PSEN activations are skipped during each access to external data

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

EA/Vpp

35

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. If EA is held

high, the device executes from internal program memory. The value on the EA pin is

latched when RST is released and any subsequent changes have no effect.

XTAL1

21

I

Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock generator

circuits.

XTAL2

20

O

Crystal 2: Output from the inverting oscillator amplifier.

22

I

Ground: 0V reference.

44

I

Power Supply: This is the power supply voltage for normal operation as well as Idle and

Power Down modes.

1

I

No Connect/Ground: This pin is a no connect pin on some derivatives, but is internally

system-level EMI characteristics.)

23

I

No Connect/Power Supply: This pin is a no connect pin on some derivatives, but is

system-level EMI characteristics.)

MNEMONIC

PIN NO.

TYPE NAME AND FUNCTION