Fault tolerant three port communications module

A communications module, comprising:

• two control ports for receiving commands from two computers, and a communication port for transferring data over a communication channel in response to said commands;
• each of said control ports including a select line which carries a select signal with true and false states, mode lines which carry codes, and a write line which carries a respective pulse in sync with each of said codes;
• each control port having its select line, mode lines, and write line coupled to a separate intra-processor command decoder and a separate inter-processor command decoder for that port;
• each intra-processor command decoder having only a single stage which generates an output signal that indicates the receipt of an intra-processor command for said module if, during any one of said pulses, a first multi-bit code occurs on said mode lines and said select line is true;
• each inter-processor command decoder having a lead stage which signals when a second multi-bit code occurs on said mode lines and said select signal is false during a first one of said pulses;
• and, having a trial state coupled to said lead stage, which generates an output signal that indicates the receipt of an inter-processor command if, during a second pulse that immediately follows said lead stage signal, the compliment of said second code occurs on said mode lines and said select line is true.