Vehicle relay device

A vehicle relay device comprising:

• a plurality of physical (PHY) modules configured to communicate in accordance with an Ethernet standard;
• and
• one PHY manager connected to the plurality of PHY modules, and configured to change an operation setting of each of the plurality of PHY modules and monitor an operation state of each of the plurality of PHY modules, wherein
• the PHY manager is individually connected to each of the plurality of PHY modules by a Management Data Input/Output (MDIO) line as a signal line for transmitting and receiving management data for monitoring and controlling an operation of each of the plurality of PHY modules,
• the PHY manager includes a Management Data Clock (MDC) output unit configured to transmit an MDC that is a clock for performing transmission and reception of the management data with each of the plurality of PHY modules, and
• when the PHY manager performs transmission and reception of the management data with at least one of the plurality of PHY modules as a communication target, the PHY manager (i) simultaneously transmits the management data to the MDIO line connected to the communication target and (ii) causes the MDIO line connected to a non-target module that is a PHY module with which the PHY manager does not perform transmission and reception of the management data to be in a high impedance state or stops transmitting the MDC to the non-target module.