AUTOMOTIVE 80C31BH80C51BH87C51

Diagrams are for pin reference only Package sizes are not to scale

270419 – 3

Pin (PDIP)

EPROM only

Do not connect reserved pins

270419 – 4

Pad (PLCC)

Figure 3 Pin Connections

PIN DESCRIPTION

Down operations

ground Provided to reduce ground bounce and im-

prove power supply bypassing

NOTE

For ROM and ROMless pin 1 is reserveddo not

connect

Port 0

Port 0 is an 8-bit open drain bidirectional IO

port As an output port each pin can sink 8 LS TTL

inputs Port 0 pins that have 1s 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 memory In this

application it uses strong internal pullups when emit-

ting 1s

Port 0 also receives the code bytes during EPROM

programming and outputs the code bytes during

program verification External pullups are required

during program verification

Port 1

Port 1 is an 8-bit bidirectional IO port with

internal pullups Port 1 pins that have 1s 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 being pulled low will source

nal pullups

Port 1 also receives the low-order address bytes

during EPROM programming and program verifica-

tion

Port 2

Port 2 is an 8-bit bidirectional IO port with

internal pullups Port 2 pins that have 1s 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 being pulled low will source

nal pullups

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

address (MOVX

DPTR) In this application it uses

strong internal pullups when emitting 1s

During accesses to external Data Memory that use

8-bit addresses (MOVX

Ri) Port 2 emits the con-

tents of the P2 Special Function Register

Port 2 also receives some control signals and the

high-order address bits during EPROM programming

and program verification

Port 3

Port 3 is an 8-bit bidirectional IO port with

internal pullups Port 3 pins that have 1s 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

ups

4