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Disable pullup resistors

Marco_Andarcia
Intellectual 370 points


Hi, 

This is a very simple problem which I am struggling to solve, I am trying to disable the internal pull up resistors on my TMS38f28069 this is what I am doing, however is not working the voltage at the pin is 2.6 V. I am using one of the development boards. 

here is my code. 

EALLOW;

//input pin for Channel1 ADD busy line
GpioCtrlRegs.GPBPUD.bit.GPIO34 = 1;
GpioCtrlRegs.GPBMUX1.bit.GPIO34 = 0;
GpioCtrlRegs.GPBDIR.bit.GPIO34 = 0;

EDIS;

  • 0
    Intellectual 370 points

    the same code works for the other GPIO's but 34 in particular doesn't work. 

  • 0 in reply to Marco_Andarcia
    Prodigy 40 points

    from my experience, GPIO34 on F2806x is very special since it is related to boot mode pin selection. In my application, I have modified schematic to add a pull up resistor on GPIO34 and leave it unused. The reason is in boot code, MCU will select boot mode according to two pins(GPIO 34, another one is GPIO17? to check).

    If we connect other components to GPIO34, the power on status of this pin is different according to your external circuit. In my application, the external circuit is not fixed. That will cause GPIO34 sometime high, sometime low at power on. If GPIO34 is detected as low level at power on, the MCU will go to "wait" mode. Then watchdog reset. This will cause a much longer reset time than normal case, untill the GPIO34 pull up resistor charges external circuit(usually capacitor...).