TIME SERIES TYPE EXCLUSIVE LOGIC SYSTEM

摘要

PURPOSE:To avoid driving of a control switch with the polarity inversion controlling signal which is wrong in terms of time series and to prevent a malfunction of a subscriber circuit, by forming a logical circuit with the call monitoring signal which monitors the state of subscribers and the polarity inversion controlling signal of a polarity inverting switch. CONSTITUTION:Current holding polarity inverting switches SW0-SW3 are connected between a call current supplying circuit BF and a telephone TEL. At the same time, the monitor signal SCN which is supplied from the circuit BF and monitors the state of subscribers is applied to a logical circuit element NOT1, and the control data D1-D3 which control the switches SW0-SW3 are applied to registers REG1-3. At the same time, the data D2 and D3 are fed to a logical circuit element OR1 via logical circuit elements NOT2 and 3 and an AND1. Then a logic is obtained between the control data and the signal SCN, and drivers DV1-3 are controlled via the registers REG1-3 to avoid driving of the switches SW0-SW3 with the polarity inversion controlling signals which are wrong in terms of time series.