| 摘要 |
PURPOSE:To block a circuit regardless of whether the circuit is in use or not, under the control that a central processor writes a block instruction into a blocking control circuit. CONSTITUTION:Cental processor CC sends out control signals (spc) and (lac) for series-parallel converter circuit SP and latch circuit LA to blocking control circuit B first, and then sends out information (sd) indicating the class of a subscriber to sp. By sp, information (sd) is converted into parallel one and transferred to LA, the output of which is used for the assignment of the class of a subscriber's telephone set to be blocked. Once blocking command (bs) is transmitted from (cc), FF of blocking control circuit B is set and bus driver D1 is driven by the set output to send a block signal to SUB1. If SUB1 is in an on-hook state, the output of loop detection circuit LD is ''0'' and, in consequence, output Q of RSFF is also ''0'' and AG1 does not conduct and is blocked. |
