FDC37C78 datasheet(49/82 Pages) MICROCHIP

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Format A Track

The Format command allows an entire track to be

formatted.

After a pulse from the IDX pin is

detected, the FDC starts writing data on the disk

including gaps, address marks, ID fields, and data

fields per the IBM System 34 or 3740 format (MFM

or FM respectively). The particular values that will

be written to the gap and data field are controlled

by the values programmed into N, SC, GPL, and D

which are specified by the host during the

command phase. The data field of the sector is

filled with the data byte specified by D. The ID

field for each sector is supplied by the host; that is,

four data bytes per sector are needed by the FDC

for C, H, R, and N (cylinder, head, sector number

and sector size respectively).

After formatting each sector, the host must send

new values for C, H, R and N to the FDC for the

next sector on the track. The R value (sector

number) is the only value that must be changed by

the host after each sector is formatted.

This

allows the disk to be formatted with nonsequential

sector addresses (interleaving). This incrementing

and formatting continues for the whole track until

the FDC encounters a pulse on the IDX pin again

and it terminates the command.

Table 28 contains typical values for gap fields

which are dependent upon the size of the sector

and the number of sectors on each track. Actual

values can vary due to drive electronics.

FORMAT FIELDS

SYSTEM 34 (DOUBLE DENSITY) FORMAT

GAP4a

80x

SYNC

12x

IAM

GAP1

50x

SYNC

12x

IDAM

GAP2

22x

SYNC

12x

DATA

GAP3

GAP 4b

SYSTEM 3740 (SINGLE DENSITY) FORMAT

GAP4a

40x

SYNC

IAM

GAP1

26x

SYNC

IDAM

GAP2

11x

SYNC

DATA

GAP3

GAP 4b

FB or

PERPENDICULAR FORMAT

GAP4a

80x

SYNC

12x

IAM

GAP1

50x

SYNC

12x

IDAM

GAP2

41x

SYNC

12x

DATA

GAP3

GAP 4b

FDC37C78 Datasheet(PDF) 49 Page - Microchip Technology

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