PC87307 datasheet(95/218 Pages) NSC

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If the system includes perpendicular drives, this command

should be issued during initialization of the FDC. Then,

when a drive is accessed for a FORMAT TRACK or WRITE

DATA command, the FDC adjusts the command parame-

ters based on the data rate. See Table 5-15.

Precompensation is set to zero for perpendicular drives at

any data rate.

Perpendicular recording type disk drives have a pre-erase

head that leads the read or write head by 200

µm, which

translates to 38 bytes at a 1 Mbps data transfer rate (19

bytes at 500 Kbps).

The increased space between the two heads requires a

larger gap 2 between the address field and data field of a

sector at 1 or 2 Mbps. See Perpendicular Format in Figure

5-20. A gap 2 length of 41 bytes (at 1 or 2 Mbps) ensures

that the preamble in the data field is completely pre-erased

by the pre-erase head.

Also, during WRITE DATA operations to a perpendicular

drive, a portion of gap 2 must be rewritten by the controller

to guarantee that the data field preamble has been pre-

erased. See Table 5-15.

Command Phase

Second Command Phase Byte

A hardware reset clears all the bits to zero (conventional

mode for all drives). PERPENDICULAR MODE command

bits may be written at any time.

The settings of bits 1 and 0 in this byte override the logical

drive configuration set by bits 5 through 2. If bits 1 and 0 are

both 0, bits 5 through 2 configure the logical disk drives as

conventional or perpendicular. Otherwise, bits 2 and 0 con-

figure them. See Table 5-16.

76543210

00010010

DC3

DC2

DC1

DC0

GDC

Bits 1,0 - Group Drive Mode Conﬁguration (GDC)

These bits configure all the logical disk drives as con-

ventional or perpendicular. If the Overwrite bit (OW, bit

7) is 0, this setting may be overridden by bits 5-2.

It is not necessary to issue the FORMAT TRACK com-

mand if all drives are conventional.

These bits are cleared to 0 by a software reset.

00 - Conventional. (Default)

01 - Perpendicular. (500 Kbps)

10 - Conventional.

11 - Perpendicular. (1 or 2 Mbps)

Bits 5-2 -Drive 3-0 Mode Conﬁguration (DC3-0)

If bits 1,0 are both 0, and bit 7 is 1, these bits configure

logical drives 3-0 as conventional or perpendicular. Bits

5-2 (DC3–0) correspond to logical drives 3-0, respec-

tively.

These bits are not affected by a software reset.

0 - Conventional drive. (Default)

It is not necessary to issue the FORMAT TRACK

command for conventional drives.

1 - Perpendicular drive.

Bit 7 - Overwrite (OW)

This bit enables or disables changes in the mode of the

logical drives by bits 5-2.

0 - Changes in mode of logical drives via bits 5-2 are

ignored. (Default)

1 - Changes enabled.

Execution Phase

Internal registers are written.

Result Phase

None.

TABLE 5-15. Effect of Drive Mode and Data Rate on FORMAT TRACK and WRITE DATA Commands

TABLE 5-16. Effect of GDC Bits on FORMAT TRACK and WRITE DATA Commands

Data Rates

Drive Mode

Length of Gap 2 in FORMAT

TRACK Command

Portion of Gap 2 Rewritten in

WRITE DATA Command

250, 300 or 500 Kbps

Conventional

Perpendicular

22 bytes

0 bytes

19 bytes

1 or 2 Mbps

Conventional

Perpendicular

22 bytes

41 bytes

0 bytes

38 bytes

GDC Bits

Drive Mode

Length of Gap 2 in

FORMAT TRACK Command

Portion of Gap 2 Rewritten in

WRITE DATA Command

Conventional

22 bytes

0 bytes

Perpendicular (

≤500 Kbps)

22 bytes

19 bytes

Conventional

22 bytes

0 bytes

Perpendicular (1 or 2 Mbps)

41 bytes

38 bytes

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