Protech Systems PPC-7400, Operation Manual

Page: 63 / 118

Chapter 3 Software Configuration
Page:3-10
PPC-740X USER
c
S MANUAL
3-9. 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 PPC-740X 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:
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