DP8473 datasheet(17/28 Pages) NSC

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Command Description (Continued)

Data Mark is read the sector is read normally If a Regular

Data Mark is found and the SK bit is set the sector is not

read bit 6 of ST2 (Control Mark) is set and the next sector

is searched for If a Regular Data Mark is found and the SK

bit is not set the sector is read bit 6 of ST2 (Control Mark)

is set and the read terminates with a normal termination

WRITE DATA

The Write Data command is very similar to the Read Data

command except that data is transferred from the mPtothe

disk rather than the other way around If the controller de-

tects the Write Protect signal bit 1 of ST1 (Not Writable) is

set and an abnormal termination is indicated

WRITE DELETED DATA

This command is the same as the Write Data Command

except a Deleted Data Mark is written at the beginning of

the Data Field instead of the normal Data Mark

READ A TRACK

This command is similar to the Read Data command except

for the following The controller starts at the index hole and

reads the sectors in their physical order not their logical

order

Even though the controller is reading sectors in their physi-

cal order it will still perform a comparison of the header ID

bytes with the Data programmed in the Command Phase

The exception to this is the sector number Internally this is

initialized to a one and then incremented for each succes-

sive sector read Whether or not the programmed Address

Field matches that read from the disk the sectors are still

read in their physical order If a header ID comparison fails

bit 2 of ST1 (No Data) is set but the operation will continue

If there is a CRC error in the Address Field or the Data Field

the read will also continue

The command will terminate when it has read the number of

sectors programmed in the EOT parameter

READ ID

This command will cause the controller to read the first Ad-

dress Field that it finds The Result Phase will contain the

header bytes that are read There is no data transfer during

the Execution Phase of this command An interrupt will be

generated when the Execution Phase is completed

FORMAT A TRACK

This command will format one track on the disk After the

index hole is detected data patterns are written on the disk

including all gaps address marks Address Fields and Data

Fields The exact details of the number of bytes for each

field is controlled by the parameters given in the Format A

Track command and the IAF (Index Address Field) bit in the

Mode command The Data Field consists of the Fill Byte

specified in the command repeated to fill the entire sector

To allow for flexible formatting the mP must supply the four

Address Field bytes (track head sector number of bytes)

for each sector formatted during the Execution Phase In

other words as the controller formats each sector it will

request four bytes through either DMA requests or inter-

rupts This allows for non-sequential sector interleaving

Some typical values for the programmable GAP size are

shown in Table XI

The Format Command terminates when the index hole is

detected a second time at which point an interrupt is gener-

ated Only the first three status bytes in the Result Phase

are significant

TABLE XI Gap Length for Various Sector Sizes

and Disk Types

Format Table for Sector Size and Data Rate

Mode

Sector

EOT

Sector

Format

Size

Code

Gap

decimal

hex

128

256

125 kbs

512

1024

2048

256

MFM

512

250 kbs

512

1024

2048

4096

128

256

512

250 kbs

1024

2048

4096

256

512

MFM

512

500 kbs

1024

2048

4096

8192

Format Table for PC Compatible Diskette Media

Media

Sector

EOT

Sector

Format

Type

Size

Code

Gap

decimal

hex

360k

512

12M

512

720k

512

144M

512

Note

Format Gap is the gap length used only for the Format command

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