PC87303 datasheet(40/114 Pages) NSC

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40 FDC Command Set Description (Continued)

418 Perpendicular Mode Command

The Perpendicular Mode command is designed to support

the unique Format and Write Data requirements of Perpen-

dicular (Vertical) Recording disk drives (4 Mbyte unformat-

ted capacity) The Perpendicular Mode command config-

ures each of the four logical drives as a perpendicular or

conventional disk drive Configuration of the four logical disk

drives is done via the D3 – 0 bits or with the GAP and WG

control bits This command should be issued during the ini-

tialization of the floppy controller

Command Phase

0100

DC3

DC2

DC1

DC0

GAP

Execution Phase

Internal registers are written

Result Phase

None

Perpendicular Recording drives operate in ‘‘Extra High Den-

sity’’ mode at 1 Mbps and are downward compatible with

144 Mbyte and 720 kbyte drives at 500 kbps (High Density)

and 250 kbps (Double Density) respectively If perpendicular

drives are present in the system this command should be

issued during initialization of the floppy controller which

configures each drive as perpendicular or conventional

Then when a drive is accessed for a Format or Write Data

command the floppy controller adjusts the Format or Write

Data parameters based on the data rate selected (see Ta-

ble 4-6)

TABLE 4-6 Effect of Drive Mode and Data Rate on Format and Write Commands

Drive

GAP2 Length

Portion of GAP2

Data Rate

Mode

Written during

Re-Written by

Format

Write Data Command

250 kbps300 kbps500 kbps

Conventional

22 Bytes

0 Bytes

Perpendicular

22 Bytes

19 Bytes

1 Mbps

Conventional

22 Bytes

0 Bytes

Perpendicular

41 Bytes

38 Bytes

TABLE 4-7 Effect of GAP and WG on Format and Write Commands

Mode

GAP2 Length

Portion of GAP2

GAP

Description

Written during

Re-Written by

Format

Write Data Command

Conventional

22 Bytes

0 Bytes

Perpendicular

22 Bytes

19 Bytes

(500 kbps)

Reserved

22 Bytes

0 Bytes

(Conventional)

Perpendicular

41 Bytes

38 Bytes

(1 Mbps)

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