missing interrupt on PIC16f690

[teragiga]

Hi
I am having some trouble on a PIC16F690:

I generate a interrupt using a monostable multivibrator of a 556 as described here and depicted here:
http://www.kpsec.freeuk.com/555timer.htm
**broken link removed**

The output is connected to a LED diode and to the RA1 port of a PIC16F690.
The output of the timer is used as an interrupt as the following code:


//Interrupt Handler
void interrupt ISR( void )
{
unsigned char dummy;
// Is this a port change interrupt and is it enabled?
if( RABIE && RABIF )
{
if( RA1==1)
{
do something.....
}
dummy = PORTA; // clear port mis-match
RABIF = 0;
}
}

The PIC is perfectly working if I connect the output of the timer to RA1. When I also connect the LED diode, the PIC stops detecting the the interrupt, as if the current/voltage was not enough since is suck up by the LED. Is there a minimal current/voltage to be detected as an interrupt by the PIC ? How can I make the PIC works together with the LED ?
Best.

 

[ericgibbs]

Do you have a resistor in series with the LED.???