Appendix A Programming the Watchdog Timer
A.1 Programming the Watchdog Timer
To program the watchdog timer, you must write a program which writes I/ O port address 440 (hex). The output data is a time interval value. The value range is from 01 (hex) to 3F (hex), and the related time interval is from 1 sec. to 63 sec.
Data Time Interval
01 | 1 sec. |
02 | 2 sec. |
03 | 3 sec. |
04 | 4 sec. |
ï | ï |
ï | ï |
ï | ï |
3F | 63 sec. |
After data entry, your program must refresh the watchdog timer by rewrit- ing the I/O port 440 (hex) while simultaneously setting it. When you want to disable the watchdog timer, your program should read I/O port 440 (hex).
The following example shows how you might program the watchdog timer :
; Enter the extended function mode , interruptible
MOV DX,2EH
MOV AL,87H
OUT DX,AL
OUT DX,AL
52 |