Activity › Forums › Questions & Troubleshooting › Issues with MEGA Serial1 › Reply To: Issues with MEGA Serial1

  • JamesC

    Member
    June 1, 2023 at 11:03 am

    Disregard the above. Below is the correct description.

    Just to close the loop on this.

    The issue here was that the MAX232 board that I mentioned above has an onboard 1k pullup resistor on the TX line. The Controllino MAXI and MEGA must also have an internal 1k pullup resistor installed on PD3 and that internal pullup resistor and the RS232 board’s 1k pullup resistor were acting as a voltage divider. This is why I was seeing an oscillation between 5V and 2.5V

    When I removed the 1k pullup resistor from the RS232 board it worked fine with Serial1.

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