Intel ECB-865 user manual 3.8Watchdog Timer Programming, Enable WDT, Re-triggerWDT, Disable WDT

User’s Manual

3.8Watchdog 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-865. 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

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