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MSPM0G3506-Q1: UART of RS485 error

jiawei yan
Prodigy 30 points

Part Number: MSPM0G3506-Q1

I used the RS485 mode of the UART peripheral for communication. I set the baud rate to 300, 600, and 1200. During these three settings, there was no normal communication between the host computer and the MCU. However, other baud rates were normal. What could be the reason for this?

  • 0
    TI__Genius 15081 points

    Hi Jiawei,

    Have you capture the waveform of TX and RX from MCU?

    Regards,

    Zoey

  • 0 in reply to Zoey Wei
    Prodigy 30 points

    As shown in the two pictures below, the first one shows the situation when the baud rate is 9600, and the second one shows the situation when the baud rate is 600. The yellow part represents the RX pin of the MCU, and the green part represents the TX pin of the MCU. However, there are some changes in the current situation.
    (1) At a baud rate of 9600, when I used the GPIO to control the CX pin of the RS485 to control the communication, if I connected the RX pin of the MCU through an oscilloscope probe, the entire communication would be interrupted.
    (2) Why are the waveforms in the above two pictures the same? This is the second problem I have discovered. That is, when I used RTS to control the communication and then used the oscilloscope probe to measure the RX and TX waveforms, at a baud rate of 600, it was actually able to communicate normally.

  • 0 in reply to jiawei yan
    TI__Genius 15081 points

    Hi Jiawei,

    Not sure if you're using the RS485 transceiver? However, I first want to determine whether this is an issue with the MCU or the transceiver. Could you clarify where the oscilloscope probes were placed when capturing the waveforms you shared—was it on the MCU side (TX/RX) or elsewhere? Also, judging by the images, the waveforms (RX/TX) on both sides appear incorrect. Is one side connected to an MCU and the other to a PC?

    Regards,

    Zoey

  • 0 in reply to Zoey Wei
    Prodigy 30 points

    I did use the RS485 converter chip. I placed the probe on the TX and RX pins of the RS485 chip. The two pictures you received were taken by photographing the TX and RX pins of the RS485 chip (only the baud rate was different). However, the waveforms on the TX and RX pins of the MCU side were the same as those in the two pictures I sent you. The reason I placed it on this side was simply because it was more convenient to use a scope to test the pins on this side compared to the MCU side. My connection method was: MCU - RS485 chip - RS485 communication adapter - USB - connected to the computer.