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Chapter 3 Software Configuration
3-10. 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 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 PC 5151 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%
(but for level 1 and 2, the tolerance is 4%), 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:
MOVAX, 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
1
F
2
E
3
D
4
C
5
B
6
A
7
9
8
8
Page:3-10
Time/sec
Level
Value
0
9
8
10
16
11
24
12
32
13
40
14
48
15
56
16
Time/sec
7
64
6
72
5
80
4
88
3
96
2
104
1
112
0
120
PC 5151 USER ' S MANUAL
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