Data transmission systems

An interface system for a computer comprising:

• a RELEASE line connected to said computer;
• a plurality of data word sources and data word sinks;
• a plurality of communications links;
• a plurality of remote interface units connected to said data sources and data sinks, each one of said remote interface units connected to a corresponding one of said communications links for transferring data words therebetween via a first I/O sub-channel;
• each of said remote interface units comprising a serializer and a deserializer for converting said data words between serial and parallel form;
• an input multiplexer connected to said serializer, and an output multiplexer connected to said deserializer
• a local interface unit, connected to said computer and at least one of said communications links for transferring input data words via a plurality of second I/O sub-channels therebetween, and comprising
• a plurality of buffers each buffer connected to a corresponding one of said communication links, each buffer comprising a plurality of locations for storing in parallel form a single input data word transferred from one of said data sources and received in bit serial form from one of said corresponding links;
• said RELEASE line connected to each of said buffers for clearing a first one of said buffers when a RELEASE signal generated by said computer on said RELEASE line is transmitted to said first one buffer, said RELEASE signal being indicative that said computer has received an input data word from said local interface unit;
• means for polling each of said buffers in turn, and being responsive to the presence of an input data word in a second one of said buffers for temporarily stopping polling of said buffers at said second one of said buffers, said means for polling being connected to said RELEASE line and responsive to said RELEASE signal from said computer to resume polling of said buffers at the next one of said buffers in turn;
• and
• transmitting means for transmitting an acknowledge data word in bit serial form to a corresponding one of said remote interface units along a corresponding one of said communications links from whose corresponding buffer an input data word has just been received by said computer for informing said remote interface unit that it may send another input data word to said local interface unit.