Abstract: A telephone intercommunication system where a plurality of stations have access to a plurality of lines. Each station has a pushbutton type keyset which is connectible to integrated circuits associated with each line and are utilized and generate signals for controlling central office switching equipment.

Abstract: A phase-locked loop is disclosed having a phase comparator, a switched lowpass filter, a voltage controlled oscillator, a loss of lock detector, and a charging circuit. The switched lowpass filter has two different bandwidths: the first bandwidth has a wide frequency response for use during acquisition periods for rapid acquisition, and a second bandwidth has a very narrow bandwidth for use during normal tracking for tight control of the voltage controlled oscillator. A loss of lock detector controls the particular filter bandwidth state by causing certain filter components to be switched in and out according to the presence or absence of phase lock condition. A charging circuit, used in conjunction with the particular lowpass filter section not operative during acquisition, charges the energy storage components used in this section of the filter to preclude transients from occurring when these components are switched back into the lowpass filter.

Abstract: An arrangement for applying the bits of a binary coded word to the inputs of respective ones of a first plurality of reiterative digital stores in a predetermined time sequence. A further means is provided for subsequently applying a code of parity bits for the said binary word to the inputs of respective ones of a second plurality of reiterative digital stores in a predetermined time sequence. And also there is a means for causing the word and parity bits to traverse their respective stores in the same sequence.As a result, the binary data can receive a dual check for correctness.

Abstract: A private telephone intercommunication system including facilities for connecting the system to a telephone central office. Common supervisory means are provided to control access to a line from each station.

Abstract: A private telephone intercommunication system including facilities for connecting the system to a telephone central office. Means are included and restrict internal calls to only two stations to insure privacy.

Abstract: A time and zone metering system wherein a central store is used to accumulate the metering pulse total for each line. The central store consists of a magnetic disc with which a line scanner is synchronized. Each line is equipped with a pulse plus bias line gate that is also wired into a gating arrangement with the timing pulses, so that a combination of the allotted time by the scanner and the presence of a metering pulse is effective to cause a temporary record to be made. Included in the system is a timing means to verify the authenticity of the metering pulses. After storage of the metering marks in the temporary store other logic is effective to place the marks in the stores reserved for a particular line.

Abstract: A private telephone intercommunication system including facilities for connecting the system to a telephone central office. Separate communication channels and supervisory means are provided for external and internal calls.