MSP430F5659: Interrupt Detect On both Edge

Renjith Mohan

Part Number: MSP430F5659
Other Parts Discussed in Thread: MSP430F5529

Hi all,

I am connected a switch (on/off switch) with a custom board board of MSP430F5659. The interrupt configured for this is in HIGH_TO_LOW transition,

But interrupt takes place int both edges. The scenario is like when the switch is on one interrupt generated, when the switch turned off there also a interrupt generated.

What may be the reason for that, Kindly Help

Attaching my code

int main(void)
{

//clock() 8MHz

    GPIO_setAsInputPinWithPullUpResistor(GPIO_PORT_P4,GPIO_PIN4);
   GPIO_enableInterrupt(GPIO_PORT_P4,GPIO_PIN4);
   GPIO_selectInterruptEdge(GPIO_PORT_P4,GPIO_PIN4,GPIO_HIGH_TO_LOW_TRANSITION);
   GPIO_clearInterrupt(GPIO_PORT_P4,GPIO_PIN4);

while(1)

{

}

#pragma vector=PORT4_VECTOR
__interrupt void Port_4(void)
{

        case P4IV_P4IFG4:
           if (P4IES & BIT4)
           {
              //interrupt generated
               GPIO_clearInterrupt(GPIO_PORT_P4,GPIO_PIN4);
           }
           break;

}

Regards,

Renjith

over 6 years ago

0 Gary Gao over 6 years ago

TI__Mastermind 39790 points

Hi Renjith

You can refer to the register level code example that from MSP430F5529
dev.ti.com/.../
If you can capture the input wave by the oscilloscope that will be better.

Best regards
Gary

0 Renjith Mohan over 6 years ago in reply to Gary Gao

Intellectual 520 points

Hi Gary,
Thank You for your quick response,
I check with a DSO and observed that de-bounce is there.
How can solve the issue ?

Regards,
Renjith

0 Bruce McKenney over 6 years ago in reply to Renjith Mohan

Guru 100745 points

De-bouncing in principle:

1) Wait for it to stop bouncing (probably some number of msec -- measure it on your DSO)

2) Clear the IFG

3) Check to see whether the switch is in the active (low in your case) position

Most switches bounce both on press and on release, which is why (3). In your case this might look like:

void ISR(void)
{
   if (P4IFG & BIT4)    // P4.4 triggered?
   {
       __delay_cycles(8000000UL/1000);   // 1ms at 8MHz
      P4IFG &= ~BIT4;   // Clear IFG now that it has stopped bouncing
      if ((P4IN & BIT4) == 0)     // Active (low)?
      {
            // Do some stuff
      }
  }
}

If your program can't afford to spin for 1ms like that, there are other (more complex) methods.

Jack Ganssle has written up more-than-you-really-wanted about debouncing. Google "ganssle debounce".

0 Renjith Mohan over 6 years ago in reply to Bruce McKenney

Intellectual 520 points

Hello Bruce,

Thank you for your Help,
Actually we are working on very time constrained Application, So 1ms can't afford.

Could you please help me with the complex method ?

Regards,
Renjith

0 Dietmar Walther over 6 years ago in reply to Renjith Mohan

TI__Genius 14165 points

Hi Renjith,

why you do not simply at a capacitor on the switch to perform debouncing via HW. If this does not help and RC filter might an option to filter for glitches.

0 Bruce McKenney over 6 years ago in reply to Renjith Mohan

Guru 100745 points

Have you read Mr. Ganssle's report? He describes some of them.

The other solutions generally amount to a periodic poll (runs all the time in the background) which reads the state of the pin. A pin state is only accepted after some number N of consecutive "votes" which agree, meaning that the pin has been (quietly) in that state for (N*period) time. It costs about the same as the above solution, but it's spread out more so you don't get bursts of time-wasting.

Or go with a hardware solution as Dietmar suggests. I defer to the electronics wizards on that.

0 Renjith Mohan over 6 years ago in reply to Bruce McKenney

Intellectual 520 points

Hello Bruce,

Thank you for your support. I read Mr. Ganssle's report.

We are planning to do the changes in H/W side.

Regards,

Renjith

0 Dietmar Walther over 6 years ago in reply to Renjith Mohan

TI__Genius 14165 points

Hi Renjith,

based on you last post I assume this thread can be closed correct?

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MSP430F5659: Interrupt Detect On both Edge