CC1110: an I/O pin which has been configured as a output pin can cause an external interrupt ! why?

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Posted by boomh

on Oct 19 2011 04:53 AM

Prodigy175 points

I am using CC1110 . I use the P0_7 as an external interrupt source which connect with a press button . so I configure P0_7 as a input pin while all other pins of P0 as output pin, like this:

P0SEL |= 0x03;
P0 |= 0x3f;
P0DIR |= 0x3f;

the interrpt configration codes are the following:

   P0IF =0;
   P0IFG = 0x00;

   PICTL |= PICTL_P0ICON;        //fall edge
   PICTL |= PICTL_P0IENH;

INT_ENABLE(INUM_P0INT, INT_ON);

and the interrupt routine are the following:

#pragma vector = P0INT_VECTOR
__interrupt void KEY_ISR(void)
{

      INT_ENABLE(INUM_P0INT, INT_OFF);
      if (P0IFG & BIT7)   {    //key

         P0IFG &= ~BIT7;      // Clear status flag for pin
         f_keyint = 1;
      }
      else if (P0IFG & BIT6)
         P0IFG &= ~BIT6;

      else if (P0IFG & BIT5)
         P0IFG &= ~BIT5;
      else if (P0IFG & BIT4)
         P0IFG &= ~BIT4;
      P0IF =0;              // Clear CPU interrupt status flag
      INT_ENABLE(INUM_P0INT, INT_ON);
}

at this time， a unusual phenomenon presented : before I press the button , external interrupt occoured frequently . the interrupt source is P0_5 or P0_4 .

what does the phenomenon mean?

any ideas? thanks a lot !

All Replies

Posted by TIABO

on Oct 25 2011 03:20 AM

Expert6765 points

What are pins P0.5 and P0.6 connected to on your board? Do you see any noise on these pins?

From what I see, your code looks ok. However, the CC1110 datasheet states in section 12.4.4 that you should always clear the IO module's interrupt flags (P0IFG register) prior to clearing the CPU's interrupt flag (IRCON.P0IF). Another tip, you should implement some kind of software debounce on your button to be sure a single button click doesn't trigger multiple interrupts.

Br,
ABO

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Posted by boomh

on Oct 27 2011 08:00 AM

Prodigy175 points

thank you for your reply!

now the phenomenon presented enen when I connect nothing at all I/O ports. (all pins are impending ). It seems that pressing key is not needed that the external interrupt occoured over and over. It looks like it works by itself .

Regards:

bob hong

Posted by Siri

on Nov 02 2011 03:04 AM

Expert4740 points

For Port 0 and port 2 you can only enable/disable interrupts for 4 and 4 pins at the time. That means that is interrupt is enabled for let's say port0 pin 4 - 7 any activity on either of these pins will cause an interrupt, even if the pin is configures as an output.

If you use port1 instead you can enable/disable interrupts for each and every pin.

Siri

Posted by boomh

on Nov 06 2011 23:28 PM

Prodigy175 points

thank you ! I think this is not very convenient for a designer. I have to change my design again!