87L52 datasheet(4/20 Pages) INTEL

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8XL525458

PIN DESCRIPTIONS

VCC Supply voltage

VSS Circuit ground

Port 0 Port 0 is an 8-bit open drain bidirectional IO

port As an output port each pin can sink several

inputs Port 0 pins that have 1’s written to them float

and in that state 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 inter-

nal pullups when emitting 1’s and can source and

sink several inputs

Port 0 also receives the code bytes during OTP

ROM programming and outputs the code bytes dur-

ing program verification External pullup resistors are

required during program verification

Port 1 Port 1 is an 8-bit bidirectional IO port with

internal pullups The Port 1 output buffers can drive

several inputs Port 1 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 1

pins that are externally pulled low will source current

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

ups

In addition Port 1 serves the functions of the follow-

ing special features of the 8XL5X

Port Pin

Alternate Function

P10

T2 (External Count

Input to Timer

Counter 2) Clock

Out

P11

T2EX (Timer

Counter 2 Capture

Reload Trigger and

Direction Control)

Port 1 receives the low-order address bytes during

OTP ROM programming and verifying

Port 2 Port 2 is an 8-bit bidirectional IO port with

internal pullups The Port 2 output buffers can drive

several inputs Port 2 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 2

pins that are externally pulled low will source current

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

ups

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 OTP ROM programming and program verifi-

cation

Port 3 Port 3 is an 8-bit bidirectional IO port with

internal pullups The Port 3 output buffers can drive

several 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

P30

RXD (serial input port)

P31

TXD (serial output port)

P32

INT0 (external interrupt 0)

P33

INT1 (external interrupt 1)

P34

T0 (Timer 0 external input)

P35

T1 (Timer 1 external input)

P36

WR (external data memory write strobe)

P37

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 VIH2 voltage is applied wheth-

er the oscillator is running or not An internal pull-

down resistor permits a power-on reset with only a

capacitor connected to VCC

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