Intel ECB-870 - Manual (Page 29)

ECB-870
ECB-870 User’s Manual 17
3.7 Watchdog Timer Programming
When the Watch-Dog Timer (WDT) function is enabled, a system reset will be generated
unless an application triggers the timer periodically within time-out period. This allows the
system to restart in an orderly way in case of any abnormal condition is found.
An optional two-port WDT is provided on ECB-870. This WDT comes with 8 possible
ranges of time intervals from 500ms to 64sec., which can be adjusted by setting jumper
positions. It could be enabled and programmed by reading I/O port 0533H or 0543H to
issue trigger continuously, and disabled by reading I/O port 0033H or 0343H. A tolerance
of 30% timer limit must be considered. For instance, if the time-out interval is set to 1
second, the WDT trigger command must be issued within 700ms at least.
The below example gives you a reference algorithm for WDT programming via I/O port
0533H and 0033H in your application programs:
Enable WDT
MOV DX, 0533H
IN AL, DX
Re-trigger WDT
MOV DX, 0533H
IN AL, DX
Disable WDT
MOV DX, 0033H
IN AL, DX