Sharp MZ-3500 User Manual download pdf (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

_____

Polarity inversion

Mzasoo

(VFO circuit): Variable frequency oscillator

Polarity inversion

_________

|~|

__________

Write pulse

Write pulse [] fl d fl R

Polarity inversion

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_

_____

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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Sharp MZ-3500 User Manual Page 56