PC87332 datasheet(40/98 Pages) NSC

40 / 98 page

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 2 Mbps and are downward com-

patible 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 com-

mand should be issued during initialization of the floppy con-

troller which configures each drive as perpendicular or con-

ventional Then when a drive is accessed for a Format or

Write Data command the floppy controller adjusts the For-

mat or Write Data parameters based on the data rate select-

ed (see Table 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 Mbps2 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 Mbps2 Mbps)

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