protech ProX-1690, User Manual, Page: 43 / 95

Chapter 3 Software Configuration
Page:3-6
Prox-1690 USER
′
S MANUAL
3-5. WATCHDOG TIMER CONFIGURATION
This board has watchdog timer function for monitoring whether the system
is still work or not after a period of time. The user can select watchdog
timer to system reset or NMI (Non Maskable interrupt) depending on the
jumper set in JP6 as described in chapter 2. This is defined at I/O port
443H
.
When you want to enable the watchdog timer, please write I/O port
443H
,
and then the system will either reset itself or perform the NMI function.
Likewise, when you want to disable the function, write I/O port
441H
, the
system will run the command to stop the Watchdog function.
In Prox-1690 watchdog function, you must write your program so when it
writes I/O port address 443 for enable watchdog and write I/O port address
441 for disable watchdog. The timer
'
s intervals have a tolerance of 25% so
you should program an instruction that will refresh the timer about every
second.
The following program shows you how to program the watch timer in your
program.
Watchdog enable program:
MOV AX, 000FH (choose the values you need; start from 0)
MOV DX, 443H
OUT DX, AX
Watchdog disable program:
MOV AX, 000FH (this value can be ignored)
MOV DX, 441H
OUT DX, AX
The Watchdog Timer control table is as follows:
Level Value Time/sec Level Value Time/sec
1 F 0 9 7 64
2 E 8 10 6 72
3 D 16 11 5 80
4 C 24 12 4 88
5 B 32 13 3 96
6 A 40 14 2 104
7 9 48 15 1 112
8 8 56 16 0 120