National Instruments GPIB-SCSI-A, Руководство пользователя

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G Mode Functions Chapter 7
GPIB-SCSI-A User Manual 7-70 © National Instruments Corp.
read - Read
Type: SCSI function
Syntax:
read logical block address, transfer
length<CR>
or
read?<CR>
Purpose: Use
read
to command the GPIB-SCSI-A to process the
Group 0 SCSI READ command.
Remarks: The GPIB-SCSI-A uses the following Command Descriptor
Block to command the Target to process
read
. Notice how
the parameters to the
read
command are used in the creation
of the Command Descriptor Block.
Bit 7 6 5 4 3 2 1 0
Byte
0 08
1 LUN Logical Block (Upper 5 bits)
2 Logical Block Address (Middle Significant Byte)
3 Logical Block Address (Least Significant Byte)
4 Transfer Length
5 VCB 00
The Logical Block Address and Transfer Length in the
Command Descriptor block above are given as parameters to
the
read
command. The LUN corresponds to the last value
assigned with the
lun
command. The VCB corresponds to
the last value assigned with the
vcb
command.
The Logical Block Address notifies the Target where the data
should be read from the device. The Transfer Length is the
number of blocks that the Target should transfer during the
Data In phase. A zero represents 256 blocks.