Abstract: A plurality of multi-functioning machines are simultaneously controlled by similar transmitter/receiver pairs, one of which is associated with a programmable controller and the other of which is associated with a machine. In the controller terminal, each transmitter of one such pair transmits a series of groups of serial command signals while its receiver receives corresponding groups of serial condition-responsive signals from the machine which update the controller. In the machine terminal, the transmitter of the other pair is connected to the controller receiver and the receiver is connected to the controller transmitter. Each transmitter derives input from a multiplexing matrix and each receiver outputs its information through a demultiplexer matrix. Each transmitter/receiver pair is driven by a free-running clock but the pair associated with the machine is slaved to the controller transmitter.