| Soft error corrected PIC clock source | |
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PIC Clock Divider II
schematic r00 source code r00 ROM image rXX flow charts Similar the the PIC12F508 clock generator below, but now based on a PIC12F675. Instead of having to compute the number of clocks per correction and then writing that error adjustment into the code space, the three clock outputs double as error setting inputs while the /Reset line is held low. Pulsing the Seconds pin low "Slows down" the clock by 0.25ppm steps and pulsing the Minutes pin low "Speeds up" the clock by 0.25ppm steps. Pulsing both the Seconds and Minutes pins low together sets the trim to zero. This yields a maximum accuracy of +/-0.125ppm over a +/-31.75ppm range (+/- 127 steps). The Hours pin outputs a PWM proportional to the internal trim where 50% is zero, <50% is "Slow down" and >50% is "Speed up" The recommneded crystal is the MC-156 32.7680KA-A0 (DK SE2412CT) and two 15pF 10% NPO capacitors. |