Texas Instruments MSP430x1xx - Manual (Page 139)

The Watchdog Timer
9-7
Watchdog Timer
9.1.3.4 Software Example
The following example illustrates the watchdog-reset operation.
; After RESET or power–up, the WDTCTL register and WDTCNT
; are cleared and the initial operating conditions are
; watchdog mode with a time interval of 32 ms.
;
;Constant definitions:
;
WDTCTL .EQU 0120h ; Address of Watchdog Timer
WDTPW .EQU 05A00h ; Password
T250MS .EQU 5 ; SSEL, IS0, IS1 set to 250 ms
T05MS .EQU 2 ; SSEL, IS0, IS1 set to 0.5 ms
CNTCL .EQU 8 ; Bit position to reset WDTCNT
TMSEL .EQU 010h ; Bit position to select timer mode
;
; As long as watchdog mode is selected, watchdog reset has
; to be done periodically through an instruction e.g.:
;
........
........
MOV #WDTPW+CNTCL,&WDTCTL
;
; To change to timer mode and a time interval of 250 ms,
; the following instruction sequence can be used:
;
MOV #WDTPW+CNTCL+TMSEL+T250MS,&WDTCTL
; Clear WDTCNT and
; select 250 ms and timer
; mode
........
........
; Note: The time interval and clear of WDTCNT should be
; modified within one instruction to avoid
; unexpected reset or interrupt
;
; Switching back to watchdog mode and a time interval of
; 0.5 ms is performed by:
;
........
........
MOV #WDTPW+CNTCL,&WDTCTL ; Reset WDT counter
;
MOV #WDTPW+T05MS,&WDTCTL ; Select watchdog mode
; and 0.5 ms
........