Master unit and communication system

A communication system comprising an I/O unit to which a device is connected, and a master unit configured to transmit a signal to the device via the I/O unit,

• wherein the master unit includes:
• a master processing circuit configured to perform signal processing;
• a first connector configured to be connected to another master unit provided in a subsequent stage of the master processing circuit;
• a second connector configured to be connected to a control device provided in a preceding stage of the master processing circuit or another master unit provided in the preceding stage;
• a branch-line terminal configured to be connected to the I/O unit;
• and
• a power supply unit configured to supply electric power to the master processing circuit,
• wherein the master unit is divided into:
• a first connector module including the first connector;
• and
• a main module including the master processing circuit, the second connector, the branch-line terminal, and the power supply unit, wherein the second connector, the branch-line terminal, and the power supply unit are connected to the master processing circuit,
• wherein each of the first connector module and the main module further includes a first connection terminal configured to connect the first connector and the master processing circuit via the I/O unit, and
• wherein the I/O unit includes:
• a preceding-stage main-line terminal and a preceding-stage branch-line terminal-configured to be connected to the first connection terminal and the branch-line terminal of the main module provided in a preceding stage of the I/O unit;
• a subsequent-stage branch-line terminal configured to be connected to the preceding-stage branch-line terminal of another I/O unit provided in a subsequent stage of the I/O unit;
• a slave processing circuit connected to the preceding-stage branch-line terminal and the subsequent-stage branch-line terminal and configured to perform input and output of a signal with respect to the master processing circuit;
• and
• a subsequent-stage main-line terminal connected to the preceding-stage main-line terminal not via the slave processing circuit and configured to be connected to the first connection terminal of the first connector module provided in the subsequent stage.