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Why Isn’t the CM4 Able to Pull the ESP32’s RX Pin Down to 0V?

I kind of have an issue somewhere and I am honestly quite stumped. I designed a board using a Raspberry CM4 and an ESP32S3. The ESP32S3 has USB-PD and is powering the CM4 through it. The ESP32 board has a CP2104 USB/UART-Bridge. Both the CP2104 and Raspberry are connected to the ESP32’s UART0.

  1. Gendos#0000

    08023560D-0AA0-41D1-9D94-ECE599D12EEA.png

  2. Gendos#0000

    For some reason the CM4 isn’t able to pull the ESP32’s RX all the way down to 0V. Anyone happen to have a clue on what may be going on here?

  3. Gendos#0000

    09FF56B04-66AD-4371-873F-9E44890667E4.png

  4. Gendos#0000

    05D4079DF-A17B-44FC-A2B8-C062C9F98C32.png

  5. Gendos#0000

    That’s quite literally it. Nothing else.

  6. Afuevu#0000

    Hello @ironside_gendos why are you connecting both to the USART0 of the ESP?

  7. bruce_wayne#0000

    “Both the CP2104 and Raspberry are connected to the ESP32’s UART0.”

    Can you explain more on this? What are you trying to do?

  8. Gendos#0000

    I meant to use both the Raspberry to flash the ESP32 as well as the CP2104.

  9. Gendos#0000

    The ESP32’s supposed to be used with the Raspberry board I designed, but if you were to use it as standalone, you could program it via USB.

  10. bruce_wayne#0000

    You can program it using the UART pins by pulling the boot pin low and resetting the chip

  11. Gendos#0000

    I know, but that’s not my issue.

  12. Gendos#0000

    My issue is: Why does the Raspberry only pull down the ESP32’s RX to 1.8V?

  13. Gendos#0000

    @afuevu_ May you be able to assist me with this?

  14. Afuevu#0000

    I think the CP2104 may be the cause of that, can you disable the CP2104 and check again

  15. Gendos#0000

    I don’t believe I can disable the CP2104 without cutting a trace.

  16. Gendos#0000

    Slight oversight on my part. Oops.

  17. Afuevu#0000

    you have more than one board? maybe you can cut a trace and try and see

  18. Afuevu#0000

    or look for a way to power the board withouth using the USB PD

  19. bruce_wayne#0000

    Doubt – Can we connect branch out multiple uart peripherals to a single pair of uart lines?

  20. Afuevu#0000

    Yeah, i will suggest you use 2 pin connectors to disable and enable. You get what i mean?

  21. Afuevu#0000

    Something like the yellow connector
    0Screenshot_from_2024-12-10_14-55-21.png

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