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HUNDREDTHS-OF-SECONDS GENERATOR

The hundredths-of-seconds generator circuit shown in the Block Diagram (Figure 1) is a state machine

that divides the incoming frequency (4096Hz) by 41 for 24 cycles and 40 for 1 cycle. This produces a

100Hz output that is slightly off during the short term, and is exactly correct every 250ms. The divide

ratio is given by:

Ratio = [41 x 24 + 40 x 1] / 25 = 40.96

Thus, the long-term average frequency output is exactly 100Hz.

Figure 2. Watchdog Timekeeper Registers