wdt.asm

本程序是本人试验AT89S51的看门狗时用的试验程序

			WDTRST	EQU	0A6H
			WDTPRG 	EQU	0A7H
			ORG 0000H
			LJMP MAIN
			ORG 0100H
			 
MAIN:		;Selected Time-out
;
;mode X1 12 clock periods per peripheral clock cycle.
;mode X2  6 clock periods per peripheral clock cycle.
;
;ORL WDTPRG,#00h   (2^14 - 1) machine cycles, 16. 3 ms @ FOSCA =12 MHz
;ORL WDTPRG,#01h   (2^15 - 1) machine cycles, 32.7 ms @ FOSCA=12 MHz
;ORL WDTPRG,#02h   (2^16 - 1) machine cycles, 65. 5 ms @ FOSCA=12 MHz
;ORL WDTPRG,#03h   (2^17 - 1) machine cycles, 131 ms @ FOSCA=12 MHz
;ORL WDTPRG,#04h   (2^18 - 1) machine cycles, 262 ms @ FOSCA=12 MHz
;ORL WDTPRG,#05h   (2^19 - 1) machine cycles, 542 ms @ FOSCA=12 MHz
;ORL WDTPRG,#06h   (2^20 - 1) machine cycles, 1.05 s @ FOSCA=12 MHz
;ORL WDTPRG,#07h   (2^21 - 1) machine cycles, 2.09 s @ FOSCA=12 MHz

			;ORL WDTPRG,#07;/*2.275s @ FOSCA=11.059200 MHz */

			;/* watchdog start sequence */
			MOV WDTRST,#1Eh;
			MOV WDTRST,#0E1h;


			MOV P0,#00H
			LCALL D500MS
			MOV P0,#0FFH
			LCALL D500MS
loop:		MOV WDTRST,#1Eh;
			MOV WDTRST,#0E1h;
			SJMP loop
D20MS:		MOV R6,#14H
D201:		ACALL D1MS
			DJNZ R6,D201
			LCALL RSTWDT
			RET
D1MS:		MOV R7,#0C0H			;1T
DD1:		NOP						;1T
			NOP						;1T
			NOP						;1T
			DJNZ R7,DD1				;2T
			LCALL RSTWDT
			RET						;2T
D250MS:		MOV R5,#0CH
DD2:		ACALL D20MS
			DJNZ R5,DD2
			RET
D500MS:		MOV R5,#19H
DD3:		ACALL D20MS
			DJNZ R5,DD3
			LCALL RSTWDT
			RET
D400MS:		MOV R5,#16H
DD4A:		ACALL D20MS
			DJNZ R5,DD3
			LCALL RSTWDT
			RET		
D1S:		MOV R5,#32H
DD4:		ACALL D20MS
			DJNZ R5,DD4
			LCALL RSTWDT
			RET
RSTWDT:		
			MOV WDTRST,#1Eh;
			MOV WDTRST,#0E1h;
			RET
		
D1M:		MOV R6,#20H
D1MA:		LCALL D1S
			DJNZ R6,D1MA
			RET	
D2S:		MOV R5,#64H
DD5:		ACALL D20MS
			DJNZ R5,DD5
			LCALL RSTWDT
			RET
			;NOP
			END