PC87306 datasheet(40/110 Pages) NSC

40 / 110 page

40 FDC Command Set Description (Continued)

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)

Looking at the second command byte DC3 – 0 corresponds

to the four logical drives

A 0 written to DCn sets drive n to conventional mode and a

1 sets drive n to perpendicular mode The OW (Overwrite)

bit offers additional control When OW e 1 the values of

DC3 – 0 (drive configuration bits) are changeable When OW

0 the internal values of DC3 – 0 are unaffected regard-

less of what is written to DC3 – 0

The function of the DCn bits must also be qualified by set-

ting both WG and GAP to 0 If WG and GAP are used (ie

not set to 00) they override whatever is programmed in the

DCn bits Table 4-7 indicates the operation of the FDC

based on the values of GAP and WG Note that when GAP

and WG are both 0 the DCn bits are used to configure each

logical drive as conventional or perpendicular DC3 – 0 is un-

affected by a software reset but WG and GAP are both

cleared to 0 after a software reset A hardware reset resets

all the bits to zero (conventional mode for all drives) The

Perpendicular Mode command bits may be rewritten at any

time

Note

When in the Perpendicular Mode for any drive at any data rate select-

ed by the DC3–0 bits write precompensation is set to zero

Perpendicular Recording type disk drives have a Pre-Erase

Head which leads the ReadWrite Head by 200 mm which

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

bytes at 500 kbps) The increased spacing between the two

heads requires a larger GAP2 between the Address Field

and Data Field of a sector at 1 Mbps (See Perpendicular

Format in Table 4-1) This GAP2 length of 41 bytes (at

1 Mbps) ensures that the Preamble in the Data Field is com-

pletely ‘‘pre-erased’’ by the Pre-Erase Head Also during

Write Data operations to a perpendicular drive a portion of

GAP2 must be rewritten by the controller to guarantee that

the Data Field Preamble has been pre-erased (see Table

4-6)

419 Read Data Command

The Read Data command reads logical sectors containing a

Normal Data Address Mark (AM) from the selected drive

and makes the data available to the host mP After the last

Command Phase byte is written the controller simulates the

Motor On time for the selected drive internally The user

must turn on the drive motor directly by enabling the appro-

priate drive and motor select disk interface outputs with the

Digital Output Register (DOR)

If Implied Seeks are enabled the controller performs a Seek

operation to the track number specified in the Command

Phase The controller also issues a Sense Interrupt for the

seek and waits the Head Settle time specified in the Mode

command

The correct ID information (track head sector bytes per

sector) for the desired sector must be specified in the com-

mand bytes See Table 4-8 Sector Size Selection for details on

the bytes per sector code In addition the End of Track

Sector Number (EOT) should be specified allowing the con-

troller to read multiple sectors The Data Length byte is a

don’t care and should be set to FFh

PC87306 Datasheet(PDF) 40 Page - National Semiconductor (TI)

PC87306 Datasheet(HTML) 40 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL