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4.4.6 TEST UNIT READY command
The following table shows the normal sequence of the TEST UNIT READY
command when used with this scanner.
Step Bus phase Initiator operation ¨ Æ Target operation
1 BUS FREE Verifies bus free
2 ARBITRATION Obtains bus>usage
right
3 SELECTION Selects target Æ
Drives BSY signal
4 MESSAGE OUT Selects logical unit Æ
5 COMMAND Specifies TEST
UNIT READY
(CDB)
Æ
6 STATUS ¨ Reports GOOD status
7 MESSAGE IN ¨ Reports message (Command
Complete)
Releases BSY signal
8 BUS FREE
(1) TEST UNIT READY command: COMMAND phase (initiator Æ target)
The TEST UNIT READY command checks whether a logical unit is ready. This
command does not request self>test. The acknowledgment of this command reported
using the status and sense data.
The CDB of this command is shown in the following illustration.
1
Byte 0
2
3
4
5
Operation code X©00π
(Reserved)
(Reserved)
Control byte
7 6 5 4 3 2 1 0
Logical unit number
4 $ 36