Department of Computer Scien

ce and Information Engineering

National Cheng Kung University, TAIWAN

HANEL

PROGRAMMING THE 82558255 Features

(cont’)

‰RD and WR

¾These two active-low control signals are inputs to the 8255¾The RD and WR signals from the 8031/51 are connected to these inputs

‰D0

– D7¾are connected to the data pins of the microcontroller ¾allowing it to send data back and forth between the controller and the 8255 chip

‰RESET

¾An active-high signal input¾Used to clear the control register

ƒWhen RESET is activated,

all ports are initialized

as input ports

(^8255) A
PA3PA2PA1PA0-RD-CSGNDA1A0PC7PC6PC5PC4PC0PC1PC2PC3PB0PB1PB2
PA4PA5PA6PA7-WRRESETD0D1D2D3D4D5D6D7VccPB7PB6PB5PB4PB3
(^1234567891011121314151617181920)
4039383736353433323130292827262524232221