Application Instructions

To use the watchdog timer, you must first decide if you want to enable hardware retriggering with an external signal. To use hardware retriggering:

• On the Prometheus, connect the external signal to pin 4 of J6 on the CPU board. J6 is located in the upper right corner of the board.
• On the Prometheus Panel I/O board, the watchdog signals are on J9 in the upper right corner of the board. See the Prometheus user manual for locations and pinouts of the CPU and panel board's I/O headers.
• On the Hercules-EBX, connect the external signal to pin 44 of J8 on the CPU board. J8 is located in the lower right corner of the board.

Next select the desired activity for the end of timer WD1. You can select any combination of the options listed in the DSCUD.H code block.

Now call the function dscWatchdogEnable() to enable and configure the watchdog timer. Once this function is called, one of two things must happen continually at a rate faster than the timeout value of WD1:

• Your program must call dscWatchdogTrigger() to retrigger the watchdog timer and restart WD1's countdown process.

• If hardware triggering is enabled, the external watchdog input signal must provide the selected active edge (rising or falling) to pin WDI.

If neither event happens before WD1 times out, the watchdog circuit will reset the system.

If needed you can use signal WDO to drive external circuitry or provide an indication of pending system reset.

To disable the watchdog timer, call dscWatchdogDisable() at any time. To reenable the watchdog timer with the same parameters, you can simply call dscWatchdogTrigger() again. To reenable the watchdog timer with different parameters, you must call dscWatchdogEnable() with the new parameters.

Example programs are provided with the CPU DSCUD examples zip file to illustrate watchdog timer operation. This program will reset the system in order to demonstrate the functionality of the watchdog timer circuit!