Abstract: A processor controlled communication switching system or PABX uses time division multiplexing with pulse width modulation of audio signals. Switching to establish communication paths between peripheral devices serviced by the system is distributed among the peripheral devices and controlled by command signals issued to the peripheral devices by a processor implemented common control. All peripheral devices transmit to the common control on a communication send line and receive signals from the common control on a communication receive line. The particular illustrated system services up to fifty two-way peripheral device ports and is inherently nonblocking.

Abstract: In a telephone set, possible mistakes in the generation of "hook flash" and "disconnect" signals, as customarily produced by operation of the hook switch and manifested as interruptions in the loop current, are avoided by a signal generating circuit which produces an accurately timed interruption of loop current, as a hook flash signal, in response to operation of a hook flash push button and which also produces another accurately timed and substantially longer interruption of loop current, as a disconnect signal, in response to operation of the hook switch.

Abstract: A decoder is disclosed for use in a communication system wherein bits of information are conveyed by the transmission, on a communication line, of code tones of distinctive frequencies each corresponding to a respective bit of information. The decoder divides an incoming signal into repetitive intervals having durations dependent on the period of the signal and provides digital measurements of the length of the interval by counting clock pulses during each interval. The digital measurements are then processed to test for persistence of the signal at a stable frequency for a predetermined time and for matching of said stabilized frequency to a recognized code tone frequency. More specifically, such decoder is disclosed as part of a larger decoder for use in, for example, a telephone communication system wherein dial numbers or other characters are communicated by way of simultaneously transmitted code tone pairs.

Abstract: A private automatic branch exchange (PABX) telephone system includes a number of stations connected to a transmission cable by appliques. By digital messages sent over a communication line in the cable, in signalling and supervision time slots, the appliques communicate with one another to make and break talking path connections between stations, which talking path connections utilize other time slots of the communication line, and to perform other signalling and supervision functions. A system clock broadcasts timing signals to the appliques over a timing line in the cable, separate from the communication line, to synchronize the operation of the appliques and to define the time slots into which the usage of the communication line is broken. The system clock also maintains traffic on the communication line by detecting the end of each signalling and supervision message and by initiating a new message upon the detection of such end of message.