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Field Replaceable Units
Descriptions of Signals
Signal
Name
Busy
-BSY
Select
-SEL
Control/Data
-C/D
Input/Output
-I/O
still tied low, so in this case it will use the soft name last downloaded. This
will allow drive access without confusing the host.
An FRU code identifies which part of the hardware is considered to have
failed. These codes turn up in sense data byte 14 and as the sense code
qualifier for sense codes 4400h (internal target failure) and 40XX (diagnostic
failure).
Although there are no actual Field Replaceable Units on HP Ultrium drives, the
following sub-assemblies can be replaced at Repair Centres:
Drive PCA
Mechanism
(Parallel SCSI only)
The SCSI interface consists of 27 signals—9 control lines, 16 data lines and 2
parity lines. A description of these signals is given in the following table.
Driven by
—
OR-tied signal used to indicate that the SCSI bus is in use.
Initiator
Used to select a target during the Selection phase.
Target
Used to select an initiator during the Reselection phase.
Target
Indicates whether control or data information is on the data
bus.
True (low)
False (high)
Target
Controls the direction of data movement on the bus with
respect to the Initiator. This signal is also used to distinguish
between Selection and Reselection phases.
Head Assembly
Front Panel
Description
Control information
Data information
Interface Implementation
23
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