Half-Size CPU Card
S B C - 6 5 7 B / H S B - 6 5 7 I
Appendix A Programming the Watchdog Timer
A-2
Programming
An onboard watchdog timer reduces the chance of disruptions which
CPLD (Compact Programmable Logical Device) interface can cause.
This is an invaluable protective device for standalone or punmanned
applications. When the watchdog timer activates (CPU processing
has come to a halt), it can reset the system, or generate an interrupt
on IRQ10, IRQ11, IRQ15, and NM1. This can be set via I/O Port
444, the function as following:
0: RESET
1: NM1
2: IRQ10
3: IRQ11
4: IRQ15
If you decide to program the watchdog timer, you must write data to
I/O port 443 (hex). The output data is a value timer. You can write
form 01 (hex) to FF (hex) while simultaneously setting it. When you
want to disable the watchdog timer, your program should read a Hex
value from I/O port 80 (hex).
The following procesude is a sample program for the watchdog
timer:
n
Type C:\DOS\Debug <ENTER>
n
To start watchdog timer and set function “Reset” type;
o 444 0<Enter>; out 444h data 0
n
To input Watchdog timers time-out interval of 5 seconds
type; o 443 05<Enter>; out 443h data 05
n
To disable the watch timer type; i80 <Enter>
The time interval data of the watchdog timer is shown in binary code
(8 bits).
Sample 2: 5 seconds
0
0
0
0
0
1
0
1
