Solution:

Programming the Watchdog Timer To program the watchdog timer, you must write a program which writes I/O port address 443 (hex). The output data is a time interval value. The value range is from 01 (hex) to 3E (hex), and the related time interval is 1 sec. to 63 sec. Data Time Interval 01 1 sec. 02 2 sec. 03 3 sec. 04 4 sec. ?. ?. ?. 3F 63 sec. After data entry, your program must refresh the watchdog timer by rewriting I/O port 443 (hex) while simultaneously setting it. When you want to disable the watchdog timer, your program should read I/O port 443 (hex). The following example shows how you might program the watchdog timer in BASIC: 10 REM Watchdog timer example program 20 OUT &H443, data REM Start and restart the watchdog 30 GOSUB 1000 REM Your application task #1, 40 OUT &H443, data REM Reset the timer 50 GOSUB 2000 REM Your application task #2, 60 OUT &H443, data REM Reset the timer 70 X=INP (&H443) REM Disable the watchdog timer 80 END 1000 REM Subroutine #1, your application task ?. ?. ?. 1070 RETURN 2000 REM Subroutine #2, your application task ?. ?. ?. 2090 RETURN