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the
maintenance panel indicators and is
theoretically available.
However, except
during maintenance, the signals are not up
long enough for the LED indicators to react.
fAULT DETECTION
The
drive contains extensive logic
to
monitor
iu internal operations and
the
OLI dialog.
If any critical component or functions oper-
ate outside of their required parameters,
~
-
the malfunction is defined as a fault.
This
raises
the
FLT line to the controller.
There are two types of fault.
Device Paul t
(SSR bit 21) indicates an internal hardware
failure.
A simplified illustration of cir-
cuits used to generate this fault is provid-
ed
by
Pigure 3-55.
Refer to the applicable
detailed operation theory (seeks, etc.) -for
further information.
DLI Error (SSIt hit
23) indicates that
the
normal controller/
drive data transfer is erroneous.
See
Figure 3-56 for
the
simplified logic: refer
to Command Operations for additional infor-
mation.
Detailed Status Bytes (OSB)
Up to five bytes of additional status infor-
mation
may
be
obtained
by
means of the OSl
through DSS commands (tags 29 through 20).
These bytes further define status
to
indicate
the cause of a fault or other status data.
These commands require a successful Seize
sequence.
Status bytes and their bit mean-
ings are defined
in
Table 3-4.
When an error occurs, the corresponding DSB
flip-flop is set to raise PLT and to store
the information.
Even through the cause of
the fault may
be
removed, the status will
continue to be stored until it is cleared
by either the specific OS- command or by
a Device Initialize signal.
.
Certain errors require that the aa.e of the
error be removed.
For example, Seek Incom-
plete (DS3 bit
2 )
requires a OS3 command to
drop the status.
However, the internal mal-
function must be cleared by prior Recalibrate
command.
In this ease, OS3 will not fully
reset the OS3 status bit: it is immediately
set again by Seek Incomplete if there has
not been a Recalibrate or its equivalent
command.
DSB bits specified as status, (Heads Retract-
ed, etc.), do not set DSB flip-flops.
-Cur-
rent status is examined only while the com-
mand is being executed.
The status itself
remains unaffected.
3-104
DIAGNOSTIC OPERATIONS
GENERAL-
Dia~os~~ ~~rati~ns
permit the controller
to check certain elements of the seek, ang-
ular
position, and write cireui ts •
See
Figure 3-57.
DIAGNOsnC COMMANDS
The
drive enters the diaqnostic mode when it
is Online, seized, and has received a Set
DiagnostiC Mode (SDK) or Set Diagnostic Es-
cape (SOE) command.
Either command sets bit
20 of the Summary Status Register.
SDK itself
has no further effect on drive operations.
~he
SDE command conditions the drive so that
it can accept an additional command set not
available durinq normal operations.
SDM
need not precede SOB.
Por further informa-
tion on diagnostic operations, refer to the
following discussions earlier
in
this
sect::i.on.-
•
Command functions are listed in Table
3-3.
•
A list of Test and Diagnostic Commands
is provided
in
the Device Level Inter-
face portion.
•
Angular Position In and Increment Sector
Counter commands are in the Sector Cir-
cuit explanation.
•
Fault conditions generated by invalid
commands are explained in Sense Oper-
ations.
•
Write Operations portion provides theory
on the write driver loqic.
The drive is released from the diagnostic
mode if the controller issues a Reset Diag-
nostic Mode
(ROM)
or Device Initialize (DIN).
Bither command also initiates an automatic
RTZS sequence.
WRITE rEST DIAGNOSTICS
The write test diagnostics (Write Test and
Write Test Check) check the write portion of
SERDES and the write toggle.
A
typical se-
quence of operations would be as follows:
NOTE
Sequeneinq is for reference only.
Actual sequencing or data patterns
may differ from this explanation.
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