PC87338 datasheet(97/221 Pages) NSC

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Table 44 shows the number of bytes in a data field

for each code.

TABLE 44. Bytes per Sector Codes

Fourth Command Phase Byte - Sectors Per Track

The value in this byte specifies how many sectors

there are in the track.

Fifth Command Phase Byte - Bytes in Gap 3

The number of bytes in gap 3 is programmable.

The number to program for Gap 3 depends on the

data transfer rate and the type of the disk drive.

Table 46 shows some typical values to use for

Gap 3.

Figure 58 illustrates the track format for each of

the formats recognized by the FORMAT TRACK

command.

Sixth Command Phase Byte - Data Pattern

This byte contains the contents of the data field.

Execution Phase

The system transfers four ID bytes (track number,

head number, sector number and bytes-per-sector

code) per sector to the Floppy Disk Controller (FDC)

in either a DMA or a non-DMA mode. Section 3.4.2 on

page 85 describes these modes.

The entire track is formatted. The data block in the

data field of each sector is filled with the data pattern

byte.

Only the first three status bytes in this phase are sig-

nificant.

Bytes-Per-Sector Code

(hex)

Bytes in Data Field

128

256

512

1024

2048

4096

8192

16384

TABLE 45. Typical Values for PC Compatible Diskette Media

Media Type

Bytes in Data

Field (decimal)

Bytes-Per-Sector

Code (hex)

End of Track (EOT)

Sector # (hex)

Bytes in Gap 2

(hex)

a. Gap 2 is specified in the command phase of read, write, scan, and verify commands. Although this is the recom-

mended value, the FDC ignores this byte in read, write, scan and verify commands.

Bytes in Gap 3

(hex)

b. Gap 3 is the suggested value for the programmable GAP3 that is used in the FORMAT TRACK command and is

illustrated in Figure 58.

360 KB

512

1.2 MB

512

720 KB

512

1.44 MB

512

2.88 MBc

c. The 2.88 MB diskette media is a barium ferrite media intended for use in perpendicular recording drives at the

data rate of up to 1 Mbps.

512

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