Zyxel XMG3927-B50A Motherboard UART Pinout


I need to reload the standard factory issue firmare into a Zyxel XMG3927-B50A that has been locked down with many features including SSH disabled. I believe that I have identified the UART pins on the bottom of the motherboard in the photo above with a red rectangle. The right most pin appears to be ground but the other poins all show 3.3v with my basic multimeter.

Does anybody have the function of the other three pins between Rx, Tx and VCC?


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  • tonygibbs16
    tonygibbs16 Posts: 839  Guru Member
    First Anniversary 10 Comments Friend Collector First Answer
    edited April 2023

    Hello @Cycle

    Welcome to the forum.

    I was wondering if someone from Zyxel was going to answer this for you.

    People in the OpenWRT community have done a lot with connecting to the UART pins on Zyxel devices, for example see https://openwrt.org/toh/zyxel/nbg6716

    - from what I have read, buy a USB to 3v3 UART connection device and only connect to TxD, RxD and Ground.

    I have not tried this myself. So you try this at your own risk. I don't work for ZyXEL.

    Kind regards,


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