Multiple COM.x modules together

  • I have an application that would need to collect data over RS485, one or two GPIOs, GPS and send it out over LTE.

    Is it correct that the M-Bus only supports two UARTS such that stacking COM.GPS, COM.LTE and COMMU together would not work?

  • Hello @mludlum

    all COM.X modules allow to select from three pairs of UART pins.

    TX can be set to: 17, 0 or 13
    RX can be set to: 16, 5 or 15

    In the COMMU module GPIO 17 and 16 are used for RS485 which leaves GPIO 0/5 and 13/15 for the two COMX modules. Unfortunately the COMMU module also uses GPIO 15 for CAN INT.

    So, no, I don't think you can make COM.GPS, COM.LTE and COMMU all work together. At least not w/o hardware modification.


  • Thanks for the information. If I didn't need CAN, there's no dip switch or API to disable it? Could I just clip the pin 15 on the COMMU M-Bus header?

  • Hello @mludlum

    no, there is no dip switch for this line - so yes, I suppose clipping the pin might work.

    Please note: I don't have the COMMU module, so I cannot actually test this.

    But, I do have the COM.LTE module and I just remembered that the SIM7600G used in the COM.LTE module also has a GPS in it. M5Stack doesn't seem to advertise this fact nor do they supply a GPS antenna, but I've just tested it and the GPS works for me.

    So for your application you won't need an extra COM.GPS module. Which reduces the number of UARTs you'll need.


  • Good to know about the GPS. I was wondering about that. Looks like it's as accurate as the COM.GPS module.
    This HAT uses the 7600G and has some specs:

    Thanks for your help!

  • The UART in question, is that the M5STACK bus IC ? What part number is it ?