The 8051 Microcontroller and Embedded

Department of Computer Scien

ce and Information Engineering

National Cheng Kung University, TAIWAN

HANEL

OTHER MODES OF THE 82558255 in Mode 1:

I/O With Handshaking

Capability

(cont

’)

¾ACKa (acknowledge for port A)
ƒactive-low input signal received at PC6 of 8255ƒThrough ACK, 8255 knows that the data at port A has been picked up by the receiving deviceƒWhen the receiving device picks up the data at port A, it must inform the 8255 through ACKƒ8255 in turn makes OBFa high, to indicate that the data at the port is now old dataƒOBFa will not go low unt

il the CPU writes a new

byte pf data to port A

¾INTRa (interrupt request for port A)

ƒActive-high signal coming out of PC3ƒThe ACK signal is a signal of limited duration