Abstract: The system receives subscriber station address information in the form of frequency coded tone signals transmitted from a calling station along a common intercom circuit, and selectively accesses a called subscriber station having a corresponding station address in order to produce a call indication ring-out thereat. The system is comprised of decoder circuitry including a digital multi-frequency tone detector for receiving and decoding station address information transmitted from a calling station, and access circuitry operatively associated with the tone detector for routing an appropriate call indication signal to the called station. Signals which appear at the output of the tone detector are delivered to the access circuitry which, in turn, initiates the call indication sequence and routes additional signals back to the tone detector for controlling it during call indication.

Abstract: The system includes a central station console and one or more remote station modules. Corresponding message-waiting indicators mounted by the central station console and each remote station module are accessed and controlled from the central station on a selective individual basis; but can be controlled alternatively from the remote station modules in order to indicate message-received. Corresponding do-not-disturb indicators mounted by the central station console and each remote station module are controlled exclusively from the latter. For telephone application, the do-not-disturb indicators additionally may be operated in a flashing mode when the associated telephone set assumes off-hook condition in order to provide call status indication.