FAILURE COUNTERMEASURE SYSTEM FOR BUTTON TELEPHONE SET

摘要

PURPOSE:To normally keep operation between a master device and other slave devices, by detecting a failure of transmission/reception function of a slave device of by the master device itself, and disconnecting a transmitter/receiver from a control line. CONSTITUTION:A control signal TxD from a master device is transmitted to a slave device designated with polling via a transmission section as a pulse signal. During the transmission, a reception section is stopped for the reception with an inhibition signal RTS but can receive a signal from the slave device with a photocoupler PC1 through the inversion of the signal RTS. The transmission/ reception circuit of the slave device makes signal transmission/reception to/ from the master device with photocouplers PC13 and PC14. A slave processor monitors an output signal IRQ of a photocoupler PC12 for transmission monitor and if a failure is detected in the said signal, it is discriminated as the failure of transmission/reception function. A signal EM is inverted and a transistor Q11 is turned off via the photocoupler PC11 to disconnect the transmission reception circuit from the control line.