Table 5-4 Typical (6-Byte) Command Descriptor Block - Data Format - Maxtor ATLAS 10K IV User Manual

SCSI Description
Field Description
Logical Block Address The 6-byte READ, SEEK, and WRITE Command Descriptor Blocks contain a 21-bit Logical
Block Address. The 10-, 12-, and 16- Command Descriptor Blocks contain a 32-bit Logical
Block Address.
Commands that require additional parameter data specify the length of the Logical Block Ad-
dress that is needed. See the specific command descriptions for more detailed information.
Relative Addressing indicates a technique used to determine the next Logical Block Address
to be operated on. The drive does not support Relative Addressing, it defaults to a value of 0,
which specifies that the Logical Block Address specifies the first logical block of a range of
logical blocks to be operated on by the command.
Transfer Length The transfer length field normally specifies the number of sectors to be transferred between the
initiator and the drive. For several commands, the transfer length indicates the number of bytes
(not sectors) to be sent. For these commands, this field may be identified by a different name
Commands that use one byte for the transfer length value allow up to 256 sectors of data to be
transferred by one command. A transfer length value of 0 indicates that 256 sectors are to be
sent. Transfer length values of 1 through 255 indicate the number of sectors to be transferred.
Commands that use multiple bytes for the transfer length value function differently. A transfer
length value of 0 indicates that no data transfer is to occur. Transfer length values of 1 or greater
indicate the number of sectors to be transferred.
Parameter List Length The Parameter List Length is used to specify the number of bytes sent during the data-out buff-
er transfer. This field is typically used for parameters that are sent to a drive (for example,
mode, diagnostic, and log parameters). A parameter list length of 0 indicates that no data is to
be transferred.
Allocation Length The Allocation Length field specifies the maximum number of bytes that the initiator has allo-
cated for returned data. The Allocation Length is used to limit the amount of data returned to
the initiator.
An Allocation Length of 0 indicates that no data is to be transferred from the drive to the initi-
ator. The drive terminates the data-in buffer transfer when the specified number of bytes have
been transferred to the initiator or when all available data has been transferred, whichever is
less.
Control Field The Control Field is the last byte of every Command Descriptor Block; its format is shown in
Figure 5-2 and described in Table 5-3.
Typical (6-Byte) Command Descriptor Block - Data Format
Table 5-4
Bit
7 6 5 4 3 2 1 0
Byte
5 Vendor Specific Reserved NACA Flag Link
Maxtor Atlas 10K IV 5-5