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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
Polarity inversion
Read waveform
MZ 3500
Advanced peak shift -
Regenerated pulse
H
*— Delayed peak shift
C b )
{VFO circuit): Variable frequency oscillator
Polarity inversion
f~J
Polarity inversion
Write pulse
J
Read waveform
6.0 40 20
0
20 40
60
( a )
j I
I
Advanced peak shift —-| t—
—•) j*- Delayed peak shift
( c )
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.
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).
5-10.
VFO circuit
1) Purpose
String of data
pulses from the FDD.
Data window
String of
separate data
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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