Sharp MZ-3500 service manual Controls during read, write, seek, and re- calibrate, Media detection

M 7.3500

5-7. Precompensate Circuit

Set the counter to 200ms.

(Actually, slightly longer than 200ms.)

K K I T E DATA

(Fig. 2)

PSO	PS1	FM	MFM	Value of LSI 63
0	0	Not changed	Not changed	1101
0	1	-	LATE(125»is)	1100
1	0	-	EARLY(125ja)	1110
1	1	-	-	-

(Table!)

WDATA-

8MHz

CLOCK

EARLY-

NOMAL-

LATE-

(Fig.3)

The precompensate circuit is used to compensate the peak shift before writing.

The FDC sends out the compensation rate to PSO and PS1 and the data bit location is shifted according to this signal. With issuance of WDATA. the value dependent on PSO and PS1 is set in the LS163. (See Table 1.) For instance, when both PSO and PS1 are low, it will set "1101 (D)" to the LS163, counted up by the 8MHz clock, and QB is sent out When it becomes "1110, 1111". When in EARLY (PSO= "H", PS1="L"), the value "1110(E)" will be set to the LS163 so that the output is issued 125ns earier than "not changed". The QB output, however, will be supplied for a period of two clock cycles.

Media is present. Media is not present.

5-9. Controls during read, write, seek, and re- calibrate

Above operations are all controlled via the FDC. 1) Control during read and write

I

READ (or WRITE)	f	I
command to FDC.
		TC-»FDC.
		HALT
		(Wait for interrupt) H-">uit staius
		is read by FDC.
DATA<- FDC
DATA-*FDC

2) Control during seek and recalibration

SEEK (or RECALB) command to FDC

I

HALT

(waits for interrupt) Read'result status from FDC.

5-8. Media detection

Insertion of a media on the MFD is detected via the signal

INDEX from the MFD. Since it takes 200ms for the media

to make a full turn, "NO MEDIA" is detected signaltNI)R t T K Y INDEX does not appear within 200ms.

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