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GD75232: Different waveform when booting up.

Part Number: GD75232

Dear Team,

My customer used eight GD75232 on their RS232 design. But recently they found that pin 5 (DY1) have different waveform behavior when booting up. 

COM4, 5 and 8 have the same waveform as below in blue. But other COM have the same waveform as below in yellow.

Could you please help to check if this is normal behavior? 

Thank you.

  • Hi Jim,

    These RS-232 output state should match their corresponding inputs. Have you checked to see if the inputs are following this same pattern as well? If so, it may be due to the MCU/UART configuration.

    Also, I'm not clear how the COM4/5/8/etc. designations relate to the schematic excerpt you provided - can you please clarify?

    Thank you,
    Max
  • Hi Max,

    Thanks for your kindly explanation.

    The input(DAx) of RS-232 buffer has three states in design for different ports,

    1. Floating

    2. Pull down to GND with a 1K resistor

    3. Pull high to 3.3V power with a 1K resistor.

    As I understanding,  the output (DY) should have two different results. VSS or VDD

           1. The input is floating or Pull high to 3.3V power with a 1K resistor, the output should be Vss(from below diagram)

           2.The input is Pull down to GND with a 1K resistor, The output should be VDD(from below diagram)

    Please correct me if I am wrong.

    Thank you.

  • Jim,

    Your understanding about the function of the driver is correct. Is there any difference about the input state between pin 5 (DY1) and COM 4, 5, 8? BTW, there are only 3 drivers in this device. Can you specify which pins COM 4, 5, 8 are?

    Regards,
    Hao
  • Hi Hao,

    My bad, I should make it more clearly.
    The customer is using ten GD75232 device for ten COM ports. (COM port 1 to 10)
    They found that COM port 4, 5 and 8 have different waveform behavior from other COM ports.
    So we think maybe the input (DAx) has different configuration setting(pullup/pulldown/floating) and cause different output result.

    Thank you.
    Jim
  • Jim,

    Thanks for your explanation. Do you know the input configuration has difference between 4/5/8 and the other COM ports? Another question: when the ports are powered up, are all connected to the same supply? Do you think they might have difference on the ramp up pattern?

    Regards,

    Hao 

  • Hi All,

    My customer has no more question so far.
    Thanks for support.

    Jim