M80C51 データシートの表示（PDF） - Oki Electric Industry

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M80C51

CMOS 8-Bit Microcontroller

Oki Electric Industry 

¡ Semiconductor

MSM80C31F/80C51F

PIN DESCRIPTION

Symbol

VSS

VCC

Port 0.0

- 0.7

Port 1.0

- 1.7

Port 2.0

- 2.7

Port 3.0

- 3.7

RESET

ALE

PSEN

EA

XTAL1

XTAL2

Description

Ground potential

Supply voltage during Normal, Idle and Power Down operation

Port 0 is an 8-bit open-drain bidirectional I/O port. It is also the mutiplexed low-order address

and data bus during accesses to external memory.

Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. It can drive CMOS inputs without

external pull-ups.

Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. It outputs the high-order address

byte during accesses to external memory. It can drive CMOS inputs without external pull-ups.

Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. It also provides various special

features, as shown below:

Port Pin

P3.0

P3.1

P3.2

P3.3

P3.4

P3.5

P3.6

P3.7

Alternate Function

RXD (serial input port)

TXD (serial output port)

INT0 (external interrupt)

INT1 (external interrupt)

T0

(Timer 0 external input)

T1

(Timer 1 external input)

WR (external data memory write strobe)

RD

(external data memory read strobe)

Port 3 can drive CMOS inputs without external pull-ups.

Reset input pin. A reset is accomplished by holding the RESET pin high for at least 1ms.

even if the oscillator has been stopped. The CPU responds by executing an internal reset. An

internal pull-down resistor permits Power-On reset using only a capacitor connected to VCC.

This pin does not receive the power down voltage since the function has been transferred to the

VCC pin.

Address Latch Enable. This output latches for latching the low byte of the address during

accesses to external memory. For this purpose, ALE is activated twice every machine cycle or

at a constant rate of 1/6th the oscillator frequency, except during an external memory access at

which time one ALE pulse is skipped. ALE can drive CMOS inputs without an external pull-up.

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

For this purpose, PSEN is activated twice every machine cycle. (However, when executing out

of external program memory, two activations of PSEN are skipped during each access to

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

It can drive CMOS inputs without an external pull-up.

External Access input pin. When EA is held high, the CPU executes out of internal program

memory (unless the program counter exceeds 0FFFH).

When EA is held low, the CPU executes only out of external program memory.

EA must not be floated.

Crystal 1 pin. It is an input to the inverting amplifier which forms the internal oscillator.

Crystal 2 pin. It is an output of the inverting amplifier that forms the internal oscillator.

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