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LEC-2026

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Appendix A: Watchdog Timer

Most systems need to be self-reliant. If an error should occur it is typically

not possible to wait for the system to be rebooted manually. In some cases,

such as apace probes, the system is simply disabled. In other cases, the

speed at which a human operator would reset the system would be too slow

to meet the uptime requirements of the product.

A watchdog timer is a piece of hardware that can be used to automatically

detect system anomalies and reset the processor if the case any problems

are found. Generally speaking, a watchdog timer is based on a counter that

counts down from an initial value to zero. The software selects the counter's

initial value and periodically restarts it. Should the counter reach zero

before the software restarts it, the software is presumed to be

malfunctioning and the processor's reset signal is asserted. Thus, the

processor will be restarted as if a human operator had cycled the power

Note:. Lanner provides sample codes in the Manual/ Driver CD under the

path:// WATCHDOG

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Lanner LEC-2026 User Manual Page 61