This might get you started.

I use this for counting parts passing on a conveyor where the parts hit a mechanical switch.

16F873A is used.

Near the top of your code
Code:
ON INTERRUPT GOTO MYINT

INTCON = %10010000
setup variables and other stuff then
Code:
LOOP:
'DO STUFF
GOTO LOOP

'#############################################
'PART COUNT
'############################################
DISABLE
MYINT:
IF PORTB.0 = 1 THEN
    PC = PC + 1
	WRITE 3,PC.BYTE0
	WRITE 4,PC.BYTE1
    READ 3,PCNT.BYTE0
	READ 4,PCNT.BYTE1
    pause 100
ELSE
	PC = PC
ENDIF
INTCON.1 = 0
RESUME
ENABLE
 'THE ABOVE WILL ALSO DEBOUNCE THE SWITCH
'#############################################
PS.
What is that in your mouth?