Chapter 3 Software Configuration
Page:3-10
PSB-701LF USER
′
S MANUAL
3-7. 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). This is defined at
I/O port
444H
and
448H
. When you want to enable the watchdog timer,
please write I/O port
444H
and
448H
, then the system will either reset itself
or perform the NMI function. If you want to stop watchdog timer, you can
read I/O port
440H
, then timer will stop count.
In PSB-701LF watchdog function, You must write your program so when it
writes I/O port address
444H
and
448H
for enable 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 of system reset enable program:
MOV
AX, 0FH (choose the values you need; start from 0)
MOV
DX,
0444H
OUT
DX,
AX
Watchdog of NMI enable program:
MOV
AX, 0FH (choose the values you need; start from 0)
MOV
DX, 0448H
OUT
DX, AX
Stop Watchdog Timer program:
MOV
DX, 0440H
In
AX , DX
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
