VMX51C900 Datasheet, PDF (42/55 Pages) List of Unclassifed Manufacturers – Versa Mix 8051 MCU with LCD Controller and ADC

VMX51C900
TABLE 54: WATCH DOG TIMER REGISTER-SYSTEM CONTROL REGISTER (SYSCON)–SFR
BFH
7
6
5
4
3
2
1
0
WDR
Unused
ALEI
Bit Mnemonic
7
WDR
[6:1] Unused
0
ALEI
Description
Watch Dog Timer Reset Bit
-
1: Enable Electromagnetic Interference
Reducer
0: Disable Electromagnetic Interference
Reducer
WDT initialization Example
The following program example shows the WDT
initialization sequence and the routine to periodically
clear it.
;*** VARIABLE DEFINITION ***
CPTR
EQU
PORTVAL EQU
020H
00H
;*** PROGRAM START HERE ****
ORG 0000h
LJMP START
;*** MAIN PROGRAM START ***
ORG 0100h
;*** CHECK IF RESET WAS CAUSED BY THE WATCHDOG TIMER
START: MOV A,SYSCON
ANL A,#80H
JNZ WDTRESET
;WDT BIT SET -> WE GOT A WDT RESET
INITWDT: MOV WDTKEY,#01EH ;UNLOCK THE WDTCTRL REG ACCESS IN
MOV WDTKEY,#0E1H ;WRITING MODE
MOV WDTCTRL,#10000010B ;CONFIG THE WATCHDOG TIMER
;BIT 7 - WDTEN=1 WATCHDOG TIMER ENABLE
;BIT 6 - UNUSED
;BIT 5 - WDTCLR=1 WATCHDOG CLEAR
;BIT 4:3 - UNUSED
;BIT 2:0 - WDTCLK=010 - WDT TIMEOUT = 8mS
MOV WDTKEY,#0E1H ;LOCK THE WDTCTRL ACCESS IN WRITING
MOV WDTKEY,#01EH
MOV PORTVAL,#00H ;INIT PORT VALUE TO 00H
WDTRESET: NOP
MOV A,PORTVAL
CPL A
MOV PORTVAL,A
MOV P1,A
;IF THE WDT CAUSE THE RESET INIT PORTVAL
;TOGGLE P1 VALUE
;*** SEQUENCE TO CLEAR THE WATCHDOG TIMER (SAME AS CONFIG)
LOOP:
;MOV WDTKEY,#01EH ;UNLOCK THE WDTCTRL REG ACCESS IN
;WRITING MODE
;MOV WDTKEY,#0E1H
;MOV WDTCTRL,#10100010B
;CONFIG THE WDT TIMER
;BIT 7 - WDTEN=1 WDT ENABLE
;BIT 6 - UNUSED
;BIT 5 - WDTCLR=1 WDT CLEAR
;BIT 4:3 - UNUSED
;BIT 2:0 - WDTCLK=010 - WDT TIMEOUT = 8mS
;MOV WDTKEY,#0E1H ;LOCK THE WDTCTRL ACCESS IN WRITING
;MOV WDTKEY,#01EH
(…)
LJMP LOOP
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