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28 SBC-455 User's Manual
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1 2 3
Watchdog timer setup
Watchdog timer time-out
signal select (JP6)
If CPU processing comes to a halt because of EMI or software
bugs, the watchdog timer can either reset the CPU or signal an
interrupt on IRQ15.
Watchdog timer time-out signal select (JP6)
Reset CPU(default) IRQ15
Watchdog timer programming
The watchdog timer must be programmed to write to I/O port
address 443 at an interval shorter than the timer's preset interval.
The timer's interval has a tolerance of ±5%, so you should pro-
gram an instruction that will refresh the timer before a time-out
occurs. The following steps illustrate how you might program the
watchdog timer.
1. Write to I/O port 443 (Hex) and designate a time-out interval.
This will enable the watchdog and set up its time-out interval.
2. Write to I/O port 080 (Hex) and any random value. This will in
turn disable the watchdog timer.