MULTIPLEX STATION

PURPOSE:To ensure self-diagnosis of a standby system by using an output of a pattern generator as a reception signal of a communication processing section in the standby system. CONSTITUTION:An output signal from a pattern generator 32a passes through a selector 31a to be a reception signal 4a and enters a communication processing section 20a. On the other hand, reception signals 4a, 4b and transmission signals 5a, 5b are given respectively to comparison processing sections 6a, 6b. when a bypass command 30b is logical 0, a communication processing section 20b is in standby and the communication processing section 20b regenerates and relays the reception signal 4b as it is and outputs the result as a transmission signal 5b. Thus, the reception signal 4b and the transmission signal 5b relating to the communication processing section 20b in the standby system are made coincident with each other.