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DISK DRIVE OPERATION
SpinPoint V40 Product Manual
63
The sector count and head values are not checked for validity by this command. If they are invalid, no error
will be posted until an illegal access is made by some other command.
6.4.10 Read Buffer (E4h)
The Read Buffer command enables the host to read the current contents of the drive's sector buffer. When
this command is issued, the drive sets BSY, sets up the sector buffer for a read operation, sets DRQ, clears
BSY, and generates an interrupt. The host then reads up to 512 bytes of data from the buffer.
The Read Buffer and Write Buffer commands are synchronized so that sequential Write Buffer (E8h) and
Read Buffer commands access the same 512 bytes within the buffer.
6.4.11 Read DMA (C8h:with retry, C9h:without retry)
This command executes in a manner similar to the Read Sector(s) command except for the following:
• The host initializes a slave-DMA channel prior to issuing the command
• 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 stopped and the status
is available.
Any unrecoverable error encountered during execution of a Read DMA command results in the termination
of data transfer prior to the sector where the error was detected. The drive generates an interrupt to indicate
that data transfer has terminated and status is available. The error posting is the same as that for the Read
Sector(s) command.
6.4.12 Read Long (22h:with retry, 23h: without retry)
The Read Long command performs similarly to the Read Sectors command except that it returns the data and
the ECC bytes appended to the data field of the desired sector. During a Read Long command, the drive does
not check the ECC bytes to determine if there has been a data error. Only single sector Read Long operations
are supported.
The transfer of the ECC bytes shall be 8 bits wide, and 4 or device native ECC bytes length.