1. A communication system for serving a plurality of communication devices each of which is connected to an associated port circuit, said system including a system controller for transmitting commands to control said port circuits and for receiving data transmitted from said port circuits, said system further comprising a plurality of port interfaces each interposed between said system controller and one of said port circuits wherein each port interface sends a command received acknowledgement signal in response to a received interface command from said system controller requesting data from an associated port circuit and wherein each port interface sends said data as an interface response to a subsequent read command from said system controller and said system controller including first means for transmitting a separate interface command to each of a preselected number of said port interfaces in a predetermined order and for receiving a separate command received acknowledgement signal from each of said preselected number of said port interfaces and second means operational after said first transmitting means for transmitting a separate read command to each of said preselected number of said port interfaces in said predetermined order and for receiving a separate interface response from each of said preselected number of said port interfaces.