Using Watch-dog Timer
This example describes how the watch-dog timer should not operate. The watch-dog timer is properly adjusted (nominal time for counting is 1024mS), but instruction used to reset it is intentionally left out so that this timer always "wins". As a result, the microcontroller is reset (state in registers remains unchanged), program starts execution from the beginning and the number in register R3 is incremented by 1 and then copied to port P1.LEDs display this number in binary format...
;************************************************************************
;* PROGRAM NAME : WatchDog.ASM
;* DESCRIPTION : After watch-dog reset, program increments number in
;* register R3 and shows it on port P1 in binary format.
;************************************************************************
;BASIC DIRECTIVES
$MOD53
$TITLE(WATCHDOG.ASM)
$PAGEWIDTH(132)
$DEBUG
$OBJECT
$NOPAGING
WMCON DATA 96H
WDTEN EQU 00000001B ; Watch-dog timer is enabled
PERIOD EQU 11000000B ; Nominal Watch-dog period is set to be 1024ms
;RESET VECTOR
CSEG AT 0
JMP XRESET ; Reset vector
CSEG
ORG 100H
XRESET: ORL WMCON,#PERIOD ; Define Watch-dog period
ORL WMCON,#WDTEN ; Watch-dog timer is enabled
MOV A,R3 ; R3 is moved to port 1
MOV P1,A
INC R3 ; Register R3 is incremented by 1
LAB: SJMP LAB ; Wait for watch-dog reset
END ; End of program
