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TMS320F280039C-Q1: What the GPIO statue when it changes from EPWM to GPIO

Shuqing Zhou
Intellectual 1745 points
Part Number: TMS320F280039C-Q1

Tool/software:

Hi experts,

I ask this for my customer.

In the initiation, they will disable the pull-up and configurate the GPIO is output. And they will keep this configuration in their next operations.

They will change the GPIO0 and GPIO1 function in the application code.

And they find when they change the GPIO from EPWM to GPIO, and if they don't use GpioDataRegs.GPACLEAR.bit.GPIOx or GpioDataRegs.GPASET.bit.GPIOx to define the sure output level in the GPIO, the GPIO will be influenced by other pin. (the red signal is the voltage of GPIO function, it have a lot of noise)

So they want to check:

1. If they disable the pull-up and configurate the GPIO is output, but they don't use GpioDataRegs.GPACLEAR.bit.GPIOx or GpioDataRegs.GPASET.bit.GPIOx to define the output voltage of this GPIO, what the statue of this pin? Is it will output high voltage or low voltage?

2. What the internal resistor of this pin? why the voltage of this pin will be influenced by other pin?

BRs

Shuqing

  • 0
    TI__Prodigy 530 points

    Hello Shuqing,

    I want to clarify what setup your customer has so I can properly answer your questions:

    Shuqing Zhou said:
    they find when they change the GPIO from EPWM to GPIO, and if they don't use GpioDataRegs.GPACLEAR.bit.GPIOx or GpioDataRegs.GPASET.bit.GPIOx to define the sure output level in the GPIO, the GPIO will be influenced by other pin.
    1. Is the influenced GPIO output configured for open-drain mode?
    2. Is the influenced GPIO externally connected to the other EPWM output?

    Best,

    Ryan

  • 0 in reply to Ryan Davitt
    TI__Intellectual 1745 points

    1. No, they keep the default configuration that is push-pull mode

    2. No.

    BRs

    Shuqing

  • 0 in reply to Shuqing Zhou
    TI__Prodigy 530 points

    Hi Shuqing,

    I talked with some other applications engineers, and here is the consensus to answer your questions:

    Without forcing the pin after configuration or reconfiguration, it will retain the previous state (so if switching from ePWM, it will retain the last state of the ePWM output), however this device has only an internal pull up resistor and no pull down. If you disable pull up, and don't force the output with GPACLEAR or GPASET, it'll be susceptible to noise, which could explain what your customer is seeing on the scope.

    Best,

    Ryan