1541 CIRCUIT THEORY
The Clock Circuits
Crystal Y1 outputs a 16Mhz clock signal. THis is input to UD5 on pin 8. UD5 is configured as a ÷ 16 frequency divider. The output of UD5 pin 12 is a 1 MHz clock signal used as the system clock (Phase 0) for the microprocessor. UE6 is a programmable
counter ( ÷ 16, ÷ 15, ÷ 14, ÷ 13) that outputs a varying frequency clock used to compensate for the difference in recording area/sector for sectors on inner tracks (Trks 1,2,3) as compared to sectors on out most tracks (Trks
33,34,35). The area/sector for inner tracks is less than the area/sector for out most tracks, so the recording clock frequency is increased when writing on inner tracks to keep the flux density constant. This clock output is on pin 12 of UE6.