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

’)

ƒWhen it goes active it makes OBFa inactive, stays low for a small amount of time and then goes back to highƒit is a rising edge of ACK that activates INTRa by making it highƒThis high signal on INTRa can be used to get the attention of the CPUƒThe CPU is informed through INTRa that the printer has received the last byte and is ready to receive another oneƒINTRa interrupts the CPU in whatever it is doing and forces it to write the next byte to port A to be printedƒIt is important to note that INTRa is set to 1 only if INTEa, OBF, and ACKa are all high ƒIt is reset to zero when

the CPU writes a byte

to port A