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AM625: Question about UART0 circuit

Oh Sangbong
Prodigy 250 points

Part Number: AM625

Tool/software:

Hello.

I have a question about the circuit while developing and using the AM6252 custom board.

I just connected the UART0 directly with a long external cable,

but it doesn't boot at all.

Do I need a pull-up/pull-down resistor to use UART0 right away?

Please answer.

Thank you.

  • 0
    TI__Intellectual 1590 points

    Hello Oh Sangbong,

    Thank you for the query.

    Below are the schematics recommendations:

    It is recommended to add pullup resistor on the UART Receive pin (UARTx_RXD).

    Recommend provisioning for series resistors on the UART interface signals (close to source) for isolation or debug.

    Also, if the UART is connected to external interface signal directly, ensure the signals are not available before the SOC supplies ramp. SOC IOs are not fail-safe.

    Please refer to below Errata while considering using UART boot

    https://www.ti.com/lit/er/sprz457h/sprz457h.pdf

    Boot i2371— Boot: ROM code may hang in UART boot mode during data transfer

    Regards,

    Lavanya M R.

  • 0 in reply to Lavanya M R
    TI__Guru**** 211040 points

    Hello Oh Sangbong,

    Oh Sangbong said:
    I just connected the UART0 directly with a long external cable,

    How long is the cable.

    SOC IOs may not be designed to drive the capacitance of the long cable. Could you shorten the cable and do a test.

    How is the external UART interface being power?

    If the UART interface is powered from a different power-source, please note that SOC IOs are not fail safe. No external inputs should be applied to the UART interface signals before the SOC supply ramps.

    Additionally, verify the IO level compatibility between external devices. An external ESD protection may be required since the cable can pick external ESD events. 

    Please note the Errata in case the errors were observed during bot / flash programming.

    Regards,

    Sreenivasa