87C51FC-20 查看數據表（PDF） - Intel

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87C51FC-20

CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLER

Intel 

AUTOMOTIVE 87C51FA FB FC FC-20

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

Some Port 2 pins receive the high-order address bits

during EPROM programming and program verifica-

tion

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 pulled low will source current

(IIL on the data sheet) because of the pullups

Port 3 also serves the functions of various special

features of the MCS-51 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 The port pins will be driven to their reset condi-

tion when a minimum VIH1 is applied whether the

oscillator is running or not An internal pulldown re-

sistor permits a power-on reset with only a capacitor

connected to VCC

ALE PROG Address Latch Enable output pulse for

latching the low byte of the address during accesses

to external memory This pin (ALE PROG) is also

the program pulse input during EPROM program-

ming for the 87C51FA FB FC

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

Throughout the remainder of this data sheet ALE

will refer to the signal coming out of the ALE PROG

pin and the pin will be referred to as the ALE PROG

pin

PSEN Program Store Enable is the read strobe to

external Program Memory

When the 87C51FA FB FC is executing code from

external Program Memory PSEN is activated twice

each machine cycle except that two PSEN activa-

tions are skipped during each access to external

Data Memory

EA VPP External Access enable EA must be

strapped to VSS in order to enable the device to

fetch code from external Program Memory locations

0000H to 0FFFFH Note however that if either of

the Program Lock bits are programmed EA will be

internally latched on reset

EA should be strapped to VCC for internal program

executions

This pin also receives the programming supply volt-

age (VPP) during EPROM programming

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 4 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’’ and in Application Note AP-486 ‘‘Oscillator

Design for Microcontrollers’’

5

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