Method for effecting one timer interrupt for multiple port communication

Abstract

A method for effecting full duplex communications through a plurality of ports of a processing apparatus having one timer. Each output and input signal is expressed as a plurality of bit time intervals. The timer is operated to establish cycles of duration equal to the bit time interval with each of the cycles being divided into sub-bits; designating one of the sub-bits within each of the cycles as a transmitting sub-bit and, upon commencement of the transmitting sub-bit, latching the output pins of appropriate ports at a signal level indicating an output signal bit for transmission at such ports and, upon completion of that latching, interrogating all of the ports for presence of an input signal; upon commencement of sub-bits other than a transmitting sub-bit, interrogating all of the ports for presence of input signals; designating sub-bits of a first cycle during which presence of an input signal is detected as initial sub-bits and identifying sub-bits immediately succeeding initial sub-bits as confirming sub-bits on a port-by-port basis; recognizing input signals detected during confirming sub-bits as true input signals and tagging ports at which true input signals are detected as true input ports; after such tagging, effecting selective interrogation of true input ports in subsequent cycles during sub-bits appearing in a sequential order corresponding to the confirming sub-bits in the first cycle, which selective interrogation of each of the true input ports continues until the input signal at respective true input ports ceases.