LIST P=16F877
#INCLUDE <P16F877.INC>
__CONFIG _XT_OSC & _WDT_OFF & _LVP_OFF
cblock 0x20
d1,d2,d3
endc
org 0x0000
init
banksel TRISB ;bank 1
movlw 0x06 ;configure all pins
movwf ADCON1 ;as digital inputs
clrf TRISB ;PortB all outs
banksel PORTA ;bank 0
main bsf PORTB,0 ;RB0 high
call delay
bcf PORTB,0 ;RB0 low
call delay
goto main ;repeat forever
delay movlw 0x03 ;0.5 second
movwf d1
movlw 0x18
movwf d2
movlw 0x02
movwf d3
delay_0 decfsz d1, f
goto $+2
decfsz d2, f
goto $+2
decfsz d3, f
goto delay_0
return
end