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COMMUNICATION • FX5U / GX WORKS3

Which channel numbers are used for FX5U serial communication?

For FX5U, the built-in RS-485 port is CH1, a communication board is CH2, and communication adapters are assigned CH3 and CH4 in order from the CPU side.

Practical explanation

The channel assignment is fixed by the hardware position.

Selecting the wrong channel is a common reason that a correctly wired serial device does not communicate.

Check in this order

  1. 1Identify the physical port/module.
  2. 2Match GX Works3 parameters to the assigned channel.
  3. 3Confirm baud rate, parity, stop bits and station number.

Last reviewed: 2 October 2026

Official source: MELSEC iQ-F FX5 User's Manual (Serial Communication)

Related verified answers

How many Modbus slaves can an FX5U master connect?Why is my FX5U RS-485 device not communicating?

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