#chip 16F877A, 20
#config HS_OSC, WDT_OFF, LVP_OFF

#define LED1 PORTB.1
#define LED2 PORTB.2
#define LED3 PORTB.3
#define LED4 PORTB.4

#define FlashDelay 125 ms

dir B1 out
dir B2 out
dir B3 out
dir B4 out

start:
 set LED4 OFF
 set LED1 ON
 wait FlashDelay
 set LED1 OFF
 set LED2 ON
 wait FlashDelay
 set LED2 OFF
 set LED3 ON
 wait FlashDelay
 set LED3 OFF
 set LED4 ON
 wait FlashDelay
goto start