Information Technology Reference
In-Depth Information
Table 3-6: The CBW contains a command descriptor block and other information
about the command.
Name
Bits
Description
dCBWSignature
32
The value 43425355h, which identifies the structure as
a CBW. The LSB (55h) transmits first on the bus.
dCBWTag
32
A value that associates this CBW with the CSW the
device will send in response.
dCBWDataTransferLength
32
If bit 7 of bmCBWFlags = 0, the number of bytes the
host will send in the data-transport phase.
If bit 7 of bmCBWFlags = 1, the number of bytes the
host expects to receive in the data-transport phase.
bmCBWFlags
8
Specifies the direction of the data-transport phase.
Bit 7 = 0 for an OUT (host-to-device) transfer.
Bit 7 = 1 for an IN (device-to-host) transfer.
If there is no data-transport phase, bit 7 is ignored.
All other bits are zero.
Reserved
4
Zero.
bCBWLUN
4
For devices with multiple LUNs, specifies the LUN the
command block is directed to. Otherwise the value is
zero.
Reserved
3
Zero.
bCBWCBLength
5
The length of the command descriptor block in the
CBWCB field in bytes. Valid values are 1-16.
Currently defined command descriptor blocks are all at
least 6 bytes.
CBWCB
128
The command block for the device to
execute.
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