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Linux/AM3359: Overshoot and undershoot of GPIO signals

Vamsi Siddhani
Expert 1420 points
Part Number: AM3359

Tool/software: Linux

Hi,

We are working on a custom board based on SITARA AM3359 Starterkit and is booting through eMMC.

SDK we are using is ti-processor-sdk-linux-am335x-evm-05.00.00.15 and kernel version is linux TI-SDK Kernel 4.14.40-g4796173fc5.

We are using UART0_CTSn (Mode 7 - GPIO1_8) and UART0_RTSn (Mode 7 - GPIO1_9) as GPIOs.

We've sent 12.5 MHz clock out on this lines and observed an overshoot of 1v and undershoot of 1.5v in the oscilloscope.

Our application requires the overshoot and undershoot to be within 500mv.

Kindly let us know if we can set us any constraints on drive strength, pull type, slew type, off-chip termination etc.. in order to achieve the same.

Looking forward for the solution.

Regards

Vamsi

  • 0
    TI__Guru**** 393215 points

    Hi,

    Drive strength cannot be adjusted, and slew will have no significant effect. As for pull type, normally internal pull resistors are disabled on outputs. I see that you have measured with a 50Ohm impedance. I would advise that you measure with a high impedance probe. If necessary, you will need to put in place external dampening circuitry (e.g. RC filters).