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TM4C123GH6PM: Inbuilt UART vs External UART on Tiva C LaunchPad

supreeth anil
Prodigy 230 points
Part Number: TM4C123GH6PM

I am trying to build a custom board for TM4C123GH6PM. As a part of this I was printing a bunch of characters on UART0 with 115200/8-N-1 settings using the inbuilt USB to Serial interface provided in the Tiva C LaunchPad. Everything worked fine.

Then I powered the board from an external supply and used a 3.3V FTDI USB to serial cable to do the same thing. This time the values are coming properly but with a lag i.e the printing speed has comedown significantly.

I tried it with different serial monitor programs with no positive outcome. I thought of changing it to some other cable like prolific serial cable but it has some driver problems with newer version of Windows and the IC which I will be using in my end product to convert USB to RS485 is based on FTDI.

Any advice and suggestions will be greatly appreciated.

New Update : I tried UART1 also with same result

  • 0
    TI__Guru**** 191886 points
    Hi,
    As far as the on-chip UART is concerned it does not know what it is connecting to, whether the ICDI (the one used in the launchPad) or the FTDI. If you are running the same application the MCU side (i.e. sending some characters to the PC) then they should produce the same. When you said some lag, I think it has more to do with the PC side. I don't know what is wrong with it. I will suggest you use the scope and probe the UART RX and TX signals and compare between the two different boards.
  • 0 in reply to Charles Tsai
    Prodigy 230 points

    Setting the latency timer value to 1 solved my problem. The default value is 16. You can access this from advanced port option for the selected com port.

    Thanks Charles for the hints.