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2014-11-01 10:44  
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Precision elapsed time/countdown timers using an Intersil ICM7217B 28-pin DIP. This circuit also uses an ICM7213 precision 1-minute/1-second time-base generator to provide a 4.1943 MHz crystal oscillator and divider, generating pulses counted by the ICM7217B, which is a 5959-maximum-count device. The thumbwheel switches allow a starting time to be entered into the counter for a preset countdown type timer, and allow the register to be set for compare functions. For instance, to make a 24-hour clock with BCD output the register can be reset with 2400 and the equals output used to reset the counter (courtesy Intersil, Inc.).