Communication semiconductor device capable of switching between redundant mode and non-redundant mode

A communication semiconductor device, comprising:

• a first communication circuit that performs a predetermined operation on a signal input and performs a signal output;
• a second communication circuit that performs a predetermined operation on a second signal input and performs a signal output;
• a first switchover function unit that is connected to one end of the first communication circuit and one end of the second communication circuit and switches an input destination and an output source of a signal with respect to the first communication circuit and the second communication circuit;
• a second switchover function unit that is connected to another end of the first communication circuit and the another end of the second communication circuit and switches an input destination and an output source of the signal with respect to the first communication circuit and the second communication circuit;
• a diagnostic circuit that is provided in each of the first communication circuit and the second communication circuit and diagnoses the first communication circuit and the second communication circuit;
• and
• a control circuit connected to the first communication circuit and the second communication circuit and the first switchover function unit and the second switchover function unit,
• wherein the control circuit includes:
• a switching function control unit that issues an input destination and output source switchover instruction to the first switchover function unit and the second switchover function unit based on a redundant/non-redundant mode switchover signal indicating an operation mode input and a diagnostic result of each diagnostic circuit,
• wherein, when the operation mode is a redundant mode, signals input to the first communication circuit and the second communication circuit are the same signal,
• wherein each of the first communication circuit and the second communication circuit includes a transmitter and a receiver, and
• each diagnostic circuit of the first communication circuit and the second communication circuit diagnoses each of the first communication circuit and the second communication circuit by comparing information input to the transmitter with information output from the receiver.