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MSP430F5529 Using the Push Button P1.1

Niloofar Eliyahoo
Intellectual 400 points

Hello,

Using the TI LaunchPad, I am trying to turn on the LEDs (at P1.0 and P4.7) by pressing the push-button (at P1.1).

Here is my code. The problem is that the LEDs toggle at the same rate and I can't stop them by pressing the push-button. It seems like the if-condition is always true.

Please let me know where is my mistake.

Thanks very much,

#include <msp430.h> 
int main(void) {
unsigned int i; //delay variable
    WDTCTL = WDTPW | WDTHOLD; // Stop watchdog timer
    P1DIR = 0x01; //set P1.0 as output and P1.1 as intput
    P4DIR = 0x80; //set P4.7 as output
P4OUT = 0x80; //set P4.7 high
while(1)
   {
if ((P1IN & 0x02) != 0x02) //if push button is pressed
{
P1OUT ^= 0x01;
P4OUT ^= 0x80;
for (i=0; i<30000; i++);
}
   }
return 0;
}
  • 0
    Guru 282680 points

    The PxOUT registers are undefined after reset; you must initialize P1.0, too.

    The for loop can be optimized away by the compiler. Use __delay_cycles() instead.

  • 0
    Guru 74080 points

    You do not have the pull-up-resistor enabled, so your input is floating when the button is not pressed. Change your code as follows:

    #include <msp430.h>

void main( void )
{
  unsigned int i; //delay variable
  
  WDTCTL = WDTPW | WDTHOLD; // Stop watchdog timer

  P1REN |= 0x02; // Enable resistor on P1.1
  P1OUT  = 0x02; // Set resistor to pull-up, P1.0 low
  P1DIR  = 0x01; // Set P1.0 as output and P1.1 as intput

  P4OUT  = 0x80; // Set P4.7 high
  P4DIR  = 0x80; // Set P4.7 as output

  while( 1 )
  {
    if( !(P1IN & 0x02) ) // If push button is pressed
    {
      P1OUT ^= 0x01;
      P4OUT ^= 0x80;

      for( i=0; i<30000; i++ );
    }
  }
}

    Dennis

  • 0 in reply to Dennis Eichmann
    Intellectual 400 points
    Thank you SO much Dennis for your help. You are right, I had to enable the pull-up resistor. That makes perfect sense. Again Thank you!

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