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Read command
Command op code: 28H
SCSI Specification: Section 14.2.5
Command block descriptor
Read data
A-61124 March 1999
Bit
7
Byte
0
1
Logical Unit Number
2
3
4
(MSB)
5
6
(MSB)
7
8
9
Vendor Unique
Descriptor
Data
Logical Unit
= 0
Number
RelAdr
= 0
Transfer Type
= 00
= 80
= 81
= 82
Transfer ID
= 0
=
Scanner Unique
Command
= length
Transfer Length
If the quantity of data is less than the transfer length blocks,
Check Condition Status is returned. Incorrect Length Indicator
(ILI) will be returned to the Request Sense that follows.
When performing continuous read commands, if a Check
Condition returns an indication the buffer is empty (sense key = B,
sense code = 80, and sense qualifier = 02), delay subsequent
read commands by at least 100 milliseconds.
*
For scanner-unique commands, a transfer length of 128 is recommended. The
command string is filled with nulls to a length of 128, ensuring the host
receives the data without generating a Check Condition for incorrect length.
6
5
4
Operation Code (28H)
Transfer Data Type
Reserved
Transfer Identification
Transfer Length
Reserved
Definition
Only one logical unit
Not supported
Image Data (raster data)
Scanner-unique command
Header
Compound Image (header, raster)
Not used when Transfer Type is 00, 81, or 82
When Transfer Type is 80, this field is used for
a scanner-unique command.
Maximum number of blocks (block size = 1
byte) to transfer.
NOTE: If Transfer Type = 80, use 128
3
2
1
Reserved
Flag
*
0
RelAdr
(LSB)
(LSB)
Link
5-19
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