60 PCA-6144V User's Manual
Programming the watchdog timer
If you decide to program the watchdog timer, you must write a
program which reads I/O port address 443 (hex) at regular
intervals. The first time your program reads the port, it enables the
watchdog timer. After that your program must read the port at time
intervals less than 2.0 seconds (as set in the BIOS). Otherwise, the
watchdog timer will activate and reset the CPU or generate an
interrupt on IRQ11. When you want to disable the watchdog timer,
your program should read I/O port 043 (hex).
If CPU processing comes to a standstill because of EMI or a
software bug your program's signals to I/O port address 443 to the
timer will be interrupted. The timer will then automatically reset
the CPU or invoke an IRQ, and data processing will continue
normally.
The following program shows how you might program the
watchdog timer in BASIC:
10
REM
Watchdog timer example program
15
REM
Watchdog timer interval set to 2 sec in BIOS
20
X=INP(&H443) REM
Enable and refresh the watchdog
30
GOSUB 1000 REM
Task #2, takes 2 sec to complete
40
X=INP(&H443) REM
Refresh the watchdog
50
GOSUB 2000 REM
Task #2, takes 2 sec to complete
60
X=INP(&H043) REM
Disable the watchdog
70
END
1000
REM
Subroutine #2, takes 2 seconds to complete
.
.
.
1070
RETURN
2000
REM
Subroutine #2, takes 2 seconds to complete
.
.
.
2090
RETURN
