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CC2674R10: Floating UART Rx pin problems with no serial hardware attached.

Joe Markel
Prodigy 150 points
Part Number: CC2674R10

Tool/software:

We are seeing issues, when the UART serial cable is not attached, with the UART Rx pin. In this case, the pin is left floating, and appears to receive duplicated Tx data.

From Hardware Team: The Rx pin appears to be floating and the Tx signal is coupling in, making it look like loopback.  Using a cable (pull-up) or an external pull-down, the problem goes away.

Setting the Rx pin with an internal PU doesn't appear to work either. For example
GPIO_setConfig(CONFIG_GPIO_UART2_CONSOLE_RX, GPIO_CFG_INPUT_INTERNAL | GPIO_CFG_IN_INT_NONE | GPIO_CFG_PULL_UP_INTERNAL); 

yields the same behavior.

Any ideas on how to correct this in software?

Thanks

  • 0
    TI__Genius 10430 points

    Joe,

    I have confirmed that in the UART2 device driver "open" call in the 7.10.02.23 version that you are using does indeed configure the RX pin configuration without internal weak pull-up. As we have synchronized offline, the IOCIOPortPullSelect() API can be used to enable the pull-up following the UART2 open call. I think as a best practice, I would probably do this before enabling RX with the UART2_rxEnable() API.

    Another alternative that I believe would also work would be to use the GPIO_setConfigAndMux() API.

    I've filed an enhancement request with the UART2 driver team to see if a configuration option for weak pull-up on the RX line can be added in the future.

    Thanks,

    Stuart