| 摘要 |
791,933. Automatic exchange equipment. STANDARD TELEPHONES & CABLES, Ltd. April 3, 1956, No. 10123/56. Addition to 753,645, [Group XL (c)]. Class 40 (4). [Also in Group XL (c)] Time division multiplexing of amplitude modulated pulses is obtained by providing a plurality of the combined modulator/demodulators disclosed in the parent Specification and switching them with pulses derived from a corresponding number of the transistor frequency dividers disclosed in Specification 784,379, [Group XL (c)]. Clock pulses applied to the dividers are divided by 25 so that each modulator/demodulator may be triggered to operate in any one of 25 time-phase positions in the multiplexed output. As applied to a telephone switching system, Fig. 4, 200 lines are connected each to a selector 41, of the kind above described, the outputs of the selectors being connected to a multiplex bus-bar 42. Selectors not in use are biased to cut-off. The passage of line current when a caller lifts his handset removes this bias and a starting impulse is applied via a selector 44 (which scans all the lines) from a selector 43 which seeks a vacant channel on the multiplex bus-bar. A further selector 45 acts as a register unit and is set by selector 43 to the same channel as the caller so as to send out dial tone and receive dialling impulses which step it into coincidence with the scanning switch 44 on to the called subscriber's channel selector. |
