Sharp MZ-3500 - Manual (Page 56)

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.
Write pulse _n_____ TL
Polarity inversion
Mzasoo
(VFO circuit): Variable frequency oscillator
Polarity inversion_________ |~|__________
Write pulse
Write pulse [] fl d fl R
Polarity inversion
J
When the output v"aveform is observed after writing a single
pluse on the floppy disk, the waveform show in (a) appiears.
Shown in (b) is two pluses of 4ps interval.
Deviation in the peak point is called peak shift. Since pluse
intervals of the MFD in actual operation are 4ps, Bps, and
8ps, the largest shift takes place when a pluse appears Bps
before or after 4ps, as shown in (c).
5-10. VFO circuit
1) Purpose
String of data
pulses from the FDD.
Data window
String of
separate data
_rL_
1_____T
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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