HP Surestore 80fx Optical Drive and Library SCSI-2 Command Reference - Page 23

SCSI Command Overview Drive Control Commands Data phase The data phase encompasses both the "data in" phase and the "data out" phase to transfer data to and from the drive. Synchronous and asynchronous data transfers are supported. The data in phase allows the target to request that data be sent to the initiator from the target. The data out phase allows the target to request that data be sent from the initiator to the target. Command phase The command phase sends the Command Descriptor Block (CDB) from the initiator to the drive. Message phase The message phase refers to a message in or a message out phase. Multiple messages may be sent during either phase. The first byte transferred in either of these phases is either a single-byte message or the first byte of a multiple-byte message. Multiple-byte messages are wholly contained within a single message phase. Message In phase allows the target to request that messages be sent to the initiator from the target. Message Out phase allows the target to request that messages be sent from the initiator to the target. The target invokes this phase in response to the attention condition created by the initiator. See Table 1-1 on page 1-5 for a list of supported messages. 1-4 Chapter 1