Specifications

5.4.6 Read Buffer command
The Read Buffer command (command code E4
H
) enables the host to
read the current contents of the drive’s sector buffer.
The Read Buffer and Write Buffer commands must be synchronized so
that sequential Write Buffer and Read Buffer commands access the
same 512 bytes within the buffer.
A Read Buffer command that is not immediately preceded by a Write
Buffer command gives unpredictable data.
5.4.7 Read DMA command
This command (command codes C8
H
and C9
H
) executes in a similar
manner to the Read Sectors command except for the following:
• The host initializes a slave-DMA channel prior to issuing the com-
mand.
• Data transfers are qualified by DMARQ and are performed by the
slave-DMA channel.
• The drive issues only one interrupt per command to indicate that data
transfer has terminated and status is available.
Any unrecoverable error encountered during execution of a Read DMA
command results in the termination of data transfer at the sector where
the error was detected. The sector in error is not transferred. The drive
generates an interrupt to indicate that data transfer has terminated and
status is available.
The error posting is the same as that of the Read Sectors command. If
the no-retry command code (C9
H
) is issued, some or all of the error
recovery procedures normally used with this command may be skipped.
5.4.8 Read Long command
The Read Long command (command codes 22
H
and 23
H
) performs
similarly to the Read Sectors command except that it returns the data
and the ECC bytes contained in the data field of the desired sector. After
transferring a single block of 512 bytes, the drive transfers the ECC bytes
one byte at a time.
During a Read Long command, the drive does not check the ECC bytes
to determine if there has been a data error. If the no-retry command code
(23
H
) is issued, some or all of the error recovery procedures normally
used with this command may be skipped. Only single-sector read-long
ATA Interface Reference Manual, Rev. C 47