Sharp MZ-3500 service manual VFO circuit, Purpose String of data Pulses from the FDD Data window

In the case of the MFM method, need to trace cycle fluc- tuation is further increased, as a peak shift is apt to occur because there are three write data cycles.

(Peak shift). Data read cycles fluctuate as the flux change point is moved forwards or backwards.

{VFO circuit): Variable frequency oscillator

Polarity inversion	f~J
Write pulse	J
Read waveform

6.040 20 0 20 40 60

( a )

When the output waveform is observed after writing a single pluse on the floppy disk, the waveform show in (a) appears. Shown in (b) is two pluses of 4jis interval.

5-10. VFO circuit

1) Purpose

String of data

pulses from the FDD.

Data window

String of separate data

MZ 3500

Write pulse

Polarity inversion

Read waveform

Advanced peak shift - *— Delayed peak shift

Regenerated pulse H

C b )

Polarity inversion

j I	I
Advanced peak shift —- t—	—•) j*- Delayed peak shift

(c)

Deviation in the peak point is called peak shift. Since pluse intervals of the MFD in actual operation are 4ns, 6/JS, and 8/^s, the largest shift takes place when a pluse appears 8/Js before or after 4/JS, as shown in (c).

n n

Data from the clock or data portion must be differentiated when read from the FDD. For this purpose a window pulse is used. In order to increase read tolerance, the VFO circuit carses the window to trace phase changes in the read data that take place during a floppy disk drive motor speed change.

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