82091AA Datasheet, PDF(147/204 Page) Intel Corporation – ADVANCED INTEGRATED PERIPHERAL (AIP)

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82091AA Datasheet, PDF (147/204 Pages) Intel Corporation – ADVANCED INTEGRATED PERIPHERAL (AIP)

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82091AA

8 5 2 DATA TRANSFER COMMANDS

All of the READ DATA WRITE DATA and VERIFY

type commands use the same parameter bytes and

return the same results information The only differ-

ence being the coding of bits 4 0 in the first byte

An implied seek will be executed if the feature was

enabled by the CONFIGURE Command This seek

is completely transparent to the user The Drive

Busy bit for the drive will go active in the Main Status

seek portion failure is reflected in the results status

normally returned for a READ WRITE DATA Com-

mand Status Register 0 (ST0) contains the error

code and C contains the cylinder that the seek

failed

8 5 2 1 Read Data

A set of nine bytes is required to place the FDC into

the Read Data Mode After the READ DATA Com-

mand has been issued the FDC loads the head (if it

is in the unloaded state) waits the specified head

settling time (defined in the SPECIFY Command)

and begins reading ID address marks and ID fields

When the sector address read from the diskette

matches with the sector address specified in the

command the FDC reads the sectorâs data field and

transfers the data to the FIFO

After completion of the read operation from the cur-

rent sector the sector address is incremented by

one and the data from the next logical sector is read

and output via the FIFO This continuous read func-

tion is called ââMulti-Sector Read Operationââ Upon

receipt of TC or an implied TC (FIFO overrun under-

run) the FDC stops sending data However the FDC

will continue to read data from the current sector

check the CRC bytes and at the end of the sector

terminate the READ DATA Command

N determines the number of bytes per sector (Table

25) If N is set to zero the sector size is set to 128

The DTL value determines the number of bytes to

be transferred If DTL is less than 128 the FDC

transfers the specified number of bytes to the host

For reads it continues to read the entire 128 byte

sector and checks for CRC errors For writes it com-

pletes the 128 byte sector by filling in zeroes If N is

not set to 00h DTL should be set to FFh and has no

impact on the number of bytes transferred

Table 25 Sector Sizes

Sector Size

128 Bytes

256 Bytes

512 Bytes

1024 Bytes

16 KBytes

The amount of data that can be handled with a sin-

gle command to the FDC depends on MT (multi-

track) and N (Number of bytes sector)

Table 26 Effects of MT and N Bits

MT N

Max Transfer

Capacity

Final Sector

Read from Disk

0 1 256 c 26 e 656

26 at side 0 or 1

1 1 256 c 52 e 13312 26 at side 1

0 2 512 c 15 e 7680 15 at side 0 or 1

1 2 512 c 30 e 15360 15 at side 1

0 3 1024 c 8 e 8192 8 at side 0 or 1

1 3 1024 c 16 e 16384 16 at side 1

The Multi-Track function (MT) allows the FDC to

read data from both sides of the diskette For a par-

ticular cylinder data will be transferred starting at

sector 1 side 0 and completing at the last sector of

the same track at side 1

If the host terminates a read or write operation in the

FDC the ID information in the result phase is depen-

dent on the state of the MT bit and EOT byte Refer

to Table 29 The termination must be normal

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 the head settling time may

be saved between subsequent reads

If the FDC detects a pulse on the INDEX pin twice

without finding the specified sector (meaning that

the disketteâs index hole passes through index de-

tect logic in the drive twice) the FDC sets the IC

147

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