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5.3 Host Commands
C141-E218 5-21
(2) READ SECTOR(S) (X’20’ or X’21’)
This command reads data of sectors specified in the Sector Count register from
the address specified in the Device/Head, Cylinder High, Cylinder Low and
Sector Number registers. Number of sectors can be specified from 1 to 256
sectors. To specify 256 sectors reading, ‘00’ is specified. For the DRQ, INTRQ,
and BSY protocols related to data transfer, see Subsection 5.4.1.
If the head is not on the track specified by the host, the device performs an
implied seek. After the head reaches to the specified track, the device reads the
target sector.
If an error occurs, retry reads are attempted to read the target sector before
reporting an error, irrespective of the R bit setting.
The DRQ bit of the Status register is always set prior to the data transfer
regardless of an error condition.
Upon the completion of the command execution, command block registers
contain the cylinder, head, and sector addresses (in the CHS mode) or logical
block address (in the LBA mode) of the last sector read.
If an unrecoverable error occurs in a sector, the read operation is terminated at the
sector where the error occurred. Command block registers contain the cylinder, the
head, and the sector addresses of the sector (in the CHS mode) or the logical block
address (in the LBA mode) where the error occurred, and remaining number of
sectors of which data was not transferred.
At command issuance (I/O registers setting contents)
1F7
H
(CM) 0 0 1 0 0 0 0 R
1F6
H
(DH) x L x DV Start head No. / LBA
[MSB]
1F5
H
(CH)
1F4
H
(CL)
1F3
H
(SN)
1F2
H
(SC)
1F1
H
(FR)
Start cylinder No. [MSB] / LBA
Start cylinder No. [LSB] / LBA
Start sector No. / LBA [LSB]
Transfer sector count
xx