National Instruments GPIB-SCSI-A, Руководство пользователя

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G Mode Functions Chapter 7
GPIB-SCSI-A User Manual 7-30 © National Instruments Corp.
hcmd (continued)
#h3 as the first
command byte
, the first byte in the
Command Descriptor Block is a 3. You must enter at least
one
command byte
. Any more are optional. The number
maximum of
command bytes
that can be entered are 25.
This limit does not impose problems as the SCSI
specification currently indicates a maximum Command
Descriptor Block size of 12 bytes. The GPIB-SCSI-A accepts
more bytes for future expansion and for SCSI devices that use
vendor uniquely determined Command Descriptor Block
lengths greater than 12 bytes.
If you use more than 25
command bytes
, you do not use at
least one
command byte
, or the value of
count
is invalid,
hcmd
aborts the operation with an error indication of EARG.
See Also: pad and Chapter 6, Programming in G Mode.
Examples:
1. This example causes the GPIB-SCSI-A to issue a Group 0 SCSI
SEEK command to the Target with a SCSI ID of 3. The Logical Unit
Number used is 2, and the command seeks to Logical Block Address
100.
ibwrt (gpibscsia, "tid 3\n", 6);
/* Request the GPIB-SCSI-A to communicate
* with the SCSI Target with an ID of 3.
*/
ibwrt (gpibscsia, "hcmd #h0b, #h40, 0, 100, 0,
0\n", 30);
/* Issue a SEEK to Logical Block Address 100.
* The SEEK command does not have a data
* phase, so you do not need to transfer
* anything to/from the Data Channel.
*/