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GPIO volt after reset give 1.1 volt without any configuration for any GPIO ??

ibrahem mostafa
Intellectual 510 points

using TIVA TM123g
I tested by a code included while {1} only 

All pins give 1.1 v except F1,F2,F3 give zero , why ??

In Data Sheet VIL max = .35*VDD = 1.1 v , so I think Tiva consider GPIO have VIL (max) after reset, but how to change it??

application depends on it:
when I wrote anther code using  GPIO Interrupt (high level) in pin and configured this pin to pull down , the Interrupt occurred in first time only after reset then don't occur waiting high level for this pin , why this happened ??

  • 0
    TI__Guru**** 244400 points
    Hello Ibrahem,

    The rating is for the pin to detected a valid 0. The output when driven 0 would be ~0V.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Intellectual 510 points
    I have Tiva C Series TM123G LaunchPad Evaluation Kit
    If you have one , Kindly build and burn this code and see the GPIO volt , it will be 1,1v !
    ::::::::::::::::::::::::::::::::::::::::::::
    #include <stdint.h>
    #include <stdbool.h>
    #include "inc/hw_types.h"
    #include "inc/hw_memmap.h"
    #include "driverlib/sysctl.h"
    #include "driverlib/gpio.h"
    int main(void)
    {

    SysCtlClockSet(SYSCTL_SYSDIV_5|SYSCTL_USE_PLL|SYSCTL_XTAL_16MHZ|SYSCTL_OSC_MAIN);

    while(1)
    {
    }
    }
  • 0 in reply to ibrahem mostafa
    Guru 47900 points

    ibrahem mostafa said:
    burn this code and see the GPIO volt , it will be 1,1v !

    Do not most all MCU GPIO pins - from all vendors - by custom and for safety - default to Inputs?

    Code shown does not alter this GPIO pin default value (as inputs) - thus those readings have less impact than you seem to suspect.

    If you configure several GPIO pins - instead - as outputs - almost certainly you will note a near 3V3 "swing" between output "high" & output "low."

  • 0 in reply to cb1
    Intellectual 510 points
    there is a strange thing ,
    I tested the same code again and the GPIOs volt are 0.3 volt !
  • 0 in reply to ibrahem mostafa
    Guru 47900 points

    Again - those readings may depend upon whether default, GPIO input state, includes pull-up/down (internal) resistors - and to some degree your measurement instrument & method.

    Configuring GPIO as outputs will remove your issue...

  • 0 in reply to ibrahem mostafa
    TI__Guru**** 244400 points
    Hello Ibrahem,

    Input pins without a Pull Up or Pull Down can catch static and may take discharge time. Suggest enabling the Pull Up or Pull down when using the GPIOs

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 47900 points
    Due to your vacation - it appears that our "Sync'ed Clocks" have drifted apart by 1 minute. (suspect that's on your end...)
  • 0 in reply to Amit Ashara
    Intellectual 510 points 
    the problem appeared when waiting for Interrupt high level , in first time after reset only go to the ISR although interrupt pin = 0 !!, then work correctly

/*************************************/
volatile uint8_t ui8LED = 2;
    //I confirmed it at startup code
     void GPIOAIntHandler(void)
 {
 GPIOIntClear (GPIO_PORTA_BASE, GPIO_INT_PIN_6 );
GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3, ui8LED);
 if (ui8LED == 8) { ui8LED = 2 ; } else { ui8LED = ui8LED * 2; }
}

    int main(void)
     {
 
 SysCtlClockSet(SYSCTL_SYSDIV_4|SYSCTL_USE_PLL|SYSCTL_XTAL_16MHZ|SYSCTL_OSC_MAIN);
    //3led
 SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
 GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, GPIO_PIN_1|GPIO_PIN_2|GPIO_PIN_3);
    //Interrupt GPIO PA6
SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);
GPIOPadConfigSet (GPIO_PORTA_BASE,GPIO_PIN_6 , GPIO_STRENGTH_2MA , GPIO_PIN_TYPE_STD_WPD);
IntMasterEnable();
 GPIOIntEnable ( GPIO_PORTA_BASE , GPIO_INT_PIN_6);
 GPIOIntTypeSet (GPIO_PORTA_BASE , GPIO_INT_PIN_6, GPIO_HIGH_LEVEL );
IntEnable(INT_GPIOA);
    
while (1)
 {
}
    
}
  • 0 in reply to ibrahem mostafa
    Intellectual 510 points
    the problem is solved when make :
    GPIOIntTypeSet (GPIO_PORTA_BASE , GPIO_INT_PIN_6, GPIO_HIGH_LEVEL );
    before :
    GPIOIntEnable ( GPIO_PORTA_BASE , GPIO_INT_PIN_6);
  • 0 in reply to ibrahem mostafa
    Guru 117855 points
    May I report that your (strange) measures of pins not configured as GPIO Outputs was - not only well answered - but served, "Upon silver platter!"
    Your post wandered from, "Failed repeat interrupt" to that of measurement of default state GPIO - which was answered in detail...
  • 0 in reply to cb1_mobile
    TI__Guru**** 244400 points
    Hello cb1

    I agree, the change of track from measured GPIO voltage to Interrupt does not bear any connection. Also while the step is correct the issue could be still a bigger problem, as HIGH LEVEL would imply that as long as the GPIO is held high, the interrupt shall always trigger, starving other peripherals.

    Regards
    Amit