A mode-selectable communications system which commands one or more remote modules from a controller unit. The controller unit issues a command signal having an address and major communications mode command. Each remote module includes a major mode identifier for receiving the command signal from the control unit through a communications link. The major mode identifier identifies an address pertaining to the module and identifies a major communications mode for that module as a command response mode or a time slot mode. The module implements a task indicated by the command mode and selects a time slot response based on the time slot mode. A time slot unique to that module is determined and the module communicates with the control unit through the communications link during that time slot.
