Read Dma (C8H) - Samsung WA31273A Technical Manual

AT INTERFACE and ATA COMMANDS
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.
6-4-9 Recalibrate (1xh)
This command moves the read/write heads from anywhere on the disk to cylinder 0.
Upon receipt of the command, the drive sets BSY and issues a seek to cylinder zero. The
drive then waits for the seek to complete before updating status, clearing BSY and
generating an interrupt. If the drive cannot reach cylinder 0, it posted a Track 0 Not
Found error.
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 be 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)

This command executes in a similar manner 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 at 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 of the Read Sector(s)
command.
6-4-12 Read Long (22h)
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.
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30 WA31273A / WA32543A / WA33203A / WA3216A / WA31083A / WA32162A