Typical (6-Byte) Command Descriptor Block - Data Format - Maxtor ATLAS 10K III Product Manual

SCSI Description
( K G N F
Logical Block Address
Transfer Length
Parameter List Length
Allocation Length
Control Field
T a b l e 5 - 4 Typical (6-Byte) Command Descriptor Block — Data Format
$ K V
$ [ V G
5 Ven-
dor
Specif-
Table 5-5 contains a description of the CDB control field.
5-4 Maxtor Atlas 10K III
The 6-byte READ, SEEK, and WRITE Command Descriptor Blocks
contain a 21-bit Logical Block Address. The 10-, 12-, and 16- Com-
mand Descriptor Blocks contain a 32-bit Logical Block Address.
Commands that require additional parameter data specify the length
of the Logical Block Address that is needed. See the specific com-
mand 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 spec-
ifies that the Logical Block Address specifies the first logical block
of a range of logical blocks to be operated on by the command.
The transfer length field normally specifies the number of sectors to
be transferred between the initiator and the drive. For several com-
mands, the transfer length indicates the number of bytes (not sec-
tors) to be sent. For these commands, this field may be identified
by a different name
Commands that use
to 256 sectors of data to be transferred by one command. A trans-
fer length value of 0 indicates that 256 sectors are to be sent.
Transfer length values of 1 through 255 indicate the number of sec-
tors to be transferred.
Commands that use
function differently. A transfer length value of 0 indicates that no
data transfer is to occur. Transfer length values of 1 or greater in-
dicate the number of sectors to be transferred.
The Parameter List Length is used to specify the number of bytes
sent during the data-out buffer transfer. This field is typically used
for parameters that are sent to a drive (for example, mode, diagnos-
tic, and log parameters). A parameter list length of 0 indicates that
no data is to be transferred.
The Allocation Length field specifies the maximum number of bytes
that the initiator has allocated 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 initiator. The drive terminates the data-in buff-
er transfer when the specified number of bytes have been trans-
ferred to the initiator or when all available data has been transferred,
whichever is less.
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.
  
Re- NACA
served
ic
& G U E T K R V K Q P
for the transfer length value allow up
Q P G D [ V G
for the transfer length value
O W N V K R N G D [ V G U
  
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