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SCSI Commands
TEST UNIT READY
Command Descriptor Block
Field Descriptions
Completion Status
The Test Unit Ready command provides a means to check that the drive is ready.
If the drive is able to accept a medium-access command without returning a Check
Condition status, then the Test Unit Ready command will result in Good status.
If the drive is unable to become operational or is in a state that requires action from
the host to make the drive ready, then the Test Unit Ready command will result in a
Check Condition status with a sense key of Not Ready.
This command does not access the medium or initiate a diagnostic routine.
Bits
Byte
7
6
0
1
Ignored LUN
2
3
4
5
Field
Bytes
Bits
Operation
0
Code
Ignored
1
5-7
Logical
Unit
Reserved
Control
5
Code
Message
Description
• The drive is ready to perform any appropriate medium access command.
00h
Good
• The drive remains in any previously set mode.
Status
• The tape is not moved.
02h
Check
Use the Request Sense command to retrieve the sense data.
Condition
Code
02h
04h
05h
06h
5
4
3
Operation Code (00h)
Reserved
Reserved
Reserved
Control
Description
The Operation Code for Test Unit Ready is 00h.
The LUN field is residual from the SCSI-1 days and is ignored.
All reserved bits must be 0.
The control field must be 0.
Message
Description
Not Ready
No cartridge is present; an immediate command
is in progress; or the eject button has been
pressed.
Hardware Error
Parity error on the SCSI bus or drive hardware
failure.
Illegal Request
The Command Descriptor Block is invalid.
Unit Attention
The cartridge was changed or the drive was re-
set.
2
1
0
Reserved
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