FDC37C78-HT datasheet(45/82 Pages) MICROCHIP

45 / 82 page

At the completion of the Read Data command, the

head is not unloaded until after the Head Unload

Time Interval (specified in the Specify command)

has elapsed. If the host issues another command

before the head unloads, then the head settling

time may be saved between subsequent reads.

If the FDC detects a pulse on the nINDEX pin

twice without finding the specified sector (meaning

that the diskette's index hole passes through index

detect logic in the drive twice), the FDC sets the IC

code in Status Register 0 to "01" indicating

abnormal termination, sets the ND bit in Status

terminates the Read Data Command.

After reading the ID and Data Fields in each

sector, the FDC checks the CRC bytes. If a

CRC error occurs in the ID or data field, the FDC

sets the IC code in Status Register 0 to "01"

indicating abnormal termination, sets the DE bit

flag in Status Register 1 to "1", sets the DD bit in

Status Register 2 to "1" if CRC is incorrect in the

field,

and

terminates

the

Read

Data

Command. Table 22 describes the effect of the

SK bit on the

Read Data command execution

and results.

Except where noted in Table 22,

the

value of the sector address is

automatically incremented (see Table 24).

Table 21 - Effects of MT and N Bits

MAXIMUM TRANSFER

CAPACITY

FINAL SECTOR READ

FROM DISK

256 x 26 = 6,656

256 x 52 = 13,312

512 x 15 = 7,680

512 x 30 = 15,360

1024 x 8 = 8,192

1024 x 16 = 16,384

26 at side 0 or 1

26 at side 1

15 at side 0 or 1

15 at side 1

8 at side 0 or 1

16 at side 1

Table 22 - Skip Bit vs Read Data Command

DATA ADDRESS

RESULTS

SK BIT

VALUE

MARK TYPE

ENCOUNTERED

SECTOR

READ?

CM BIT OF

ST2 SET?

DESCRIPTION OF

RESULTS

Normal Data

Deleted Data

Normal Data

Deleted Data

Yes

Normal

termination.

Address not

incremented. Next

sector not

searched for.

Normal

termination.

Normal

termination. Sector

not read

("skipped").

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