National Instruments GPIB-SCSI-A, Руководство пользователя

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Programming in G Mode Chapter 6
GPIB-SCSI-A User Manual 6-12 © National Instruments Corp.
Commands That Require a Data Out Phase
If the command requires a Data Out phase, the Target completes the
following phase sequence after Selection:
1. The Message Out phase if the Target responds to the SCSI ATN*
signal. The message that the GPIB-SCSI-A sends to the Target is an
IDENTIFY message. This IDENTIFY contains the Logical Unit
Number set with the
lun
command. IDENTIFY also contains the bit
that indicates that the GPIB-SCSI-A supports the
disconnection/reconnection feature of the SCSI. This phase is optional,
but if it does not occur, disconnection/reconnection is not possible.
2. The Command phase
3. The Data Out phase. The Target may disconnect/reconnect.
4. The Status phase
5. The Message In phase
Disconnection/Reconnection
The Target can disconnect from the SCSI bus between the Command and
Status phases to complete a time-consuming task. When finished, the
Target reconnects. However, this is only possible if the GPIB-SCSI-A is
able to send the IDENTIFY message to the Target during the Message Out
phase.
If the disconnection/reconnection occurs before data transfer has completed,
the data phase should assert after reconnection. If it does not, the EPHS
error indication results.
If the Target attempts a disconnection/reconnection, the Target completes
the following phase sequence:
1. The Message In phase (to alert the GPIB-SCSI-A that the Target is
about to disconnect from the SCSI by releasing BSY*). All messages
received are placed into the Command and Status Channel buffer.
2. The Bus Free phase (by releasing BSY*)