MD80C51FB 查看數據表（PDF） - Intel

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MD80C51FB

CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLER

Intel 

M80C51FB

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 pullups when emitting 1’s Dur-

ing accesses to external Data Memory that use 8-bit

addresses (MOVX Ri) Port 2 emits the contents of

the P2 Special Function Register

Port 3 Port 3 is an 8-bit bidirectional I O port with

internal pullups The Port 3 output buffers can drive

LS TTL inputs Port 3 pins that have 1’s written to

them are pulled high by the internal pullups and in

that state can be used as inputs As inputs Port 3

pins that are externally being pulled low will source

current (IIL on the data sheet) because of the pull-

ups

Port 3 also serves the functions of various special

features of the M8051 Family as listed below

Port Pin

Alternate Function

P3 0

P3 1

P3 2

P3 3

P3 4

P3 5

P3 6

P3 7

RXD (serial input port)

TXD (serial output port)

INT0 (external interrupt 0)

INT1 (external interrupt 1)

T0 (Timer 0 external input)

T1 (Timer 1 external input)

WR (external data memory write strobe)

RD (external data memory read strobe)

RST Reset input A high on this pin for two machine

cycles while the oscillator is running resets the de-

vice An internal pulldown resistor permits a power-

on reset with only a capacitor connected to VCC

ALE Address Latch Enable output pulse for latching

the low byte of the address during accesses to ex-

ternal memory

In normal operation ALE is emitted at a constant

rate of the oscillator frequency and may be used

for external timing or clocking purposes Note how-

ever that one ALE pulse is skipped during each ac-

cess to external Data Memory

PSEN Program Store Enable is the read strobe to

external Program Memory

When the M80C51FB is executing code from exter-

nal Program Memory PSEN is activated twice each

machine cycle except that two PSEN activations

are skipped during each access to external Data

Memory

EA External Access enable EA must be strapped to

VSS in order to enable the device to fetch code from

external Program Memory

XTAL1 Input to the inverting oscillator amplifier

XTAL2 Output from the inverting oscillator amplifier

OSCILLATOR CHARACTERISTICS

XTAL1 and XTAL2 are the input and output respec-

tively of an inverting amplifier which can be config-

ured for use as an on-chip oscillator as shown in

Figure 3 Either a quartz crystal or ceramic resonator

may be used More detailed information concerning

the use of the on-chip oscillator is available in Appli-

cation Note AP-155 ‘‘Oscillators for Microcontrol-

lers ’’

To drive the device from an external clock source

XTAL1 should be driven while XTAL2 floats as

shown in Figure 4 There are no requirements on the

duty cycle of the external clock signal since the in-

put to the internal clocking circuitry is through a di-

vide-by-two flip-flop but minimum and maximum

high and low times specified on the data sheet must

be observed

C1 C2 e 30 pF g10 pF for Crystals

e 10 pF for Ceramic Resonators

271172 – 4

Figure 3 Oscillator Connections

4

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