Optical Drive and Library SCSI-2 Command Reference

SCSI Command Overview
Drive Control Commands
Chapter 1 1-17
SCSI Command OverviewSCSI Command Overview
Unit Attention Condition
A unit attention condition for a logical unit begins for each initiator for
any of the following conditions:
• Poweron or Reset
•Disk Loaded
• Micro Code Change
•Inquiry Data Change
• Mode Select Data Change
The unit attention condition persists for each initiator until that initiator
issues a command to the logical unit other than Request Sense or Inquiry
for which the target reports a CHECK CONDITION status. If the next
command from that initiator to the logical unit (following the CHECK
CONDITION status) is Request Sense, the Unit Attention sense key is
returned. (If any command other than Request Sense is received, the
unit attention condition is lost.)
If an Inquiry Command is received from an initiator with a pending unit
attention condition (before the target reports CHECK CONDITION
status), the target performs the Inquiry Command and does not clear the
unit attention.
If a Request Sense Command is received from an initiator with a pending
unit attention condition (before the target reports a CHECK
CONDITION status), the target discards any pending sense data,
reports a Unit Attention sense key, and clears the unit attention
condition for that initiator.