Seek Operations; General - Honeywell BR3C9 Operation Manual

Note that the drive may be in the standby
state and still execute commands not involv-
ing seeks, reads, or writes. To complete a
Summary Status Request for example, the drive
must
be
powered up but need not even have a
pack installed.
As an example of execution sequence assume
that the unit is seized and that a cylinder
Out Lower (COL) command has been issued. See
Figure 3-18. Sequencing is then as follows:
1. Controller places the command byte on
the Command Code Lines.
2.
Drive decodes the command (000 111) as
Cylinder Out Lower. Since OCO=O, En-
able Serial Read In is generated inter-
nally.
3. Controller raises Device Command Strobe.
The following occur if the command byte
plus parity is not odd:
a. Command Parity Error is generated.
b. Bit 27 of DSl sets.
c. DLI Fault comes up.
d. FLT returned to controller.
4. Controller raises S.erial Wri te Out.
5. SRI Out FF (Figure 3-18) sets to raise
Serial Read In.
6.
Controller drops Serial Write Out.
7. With Serial Write Out down, single-shot
DCgl triggers and remains up for one
microsecond. This raises CB I Sample,
causing the following:
a. Logic verifies that Cylinder Out
Upper preceded Cylinder Out Lower.
If not, Invalid Command Sequence
(bit 24 of DS1) and DLI Fault are
set.
b. Data on bidirectional lines loaded
into Cylinder Address Register. See
Figure 3-17. (In the case of Cyl-
inder Out Lower, bit 28 was stored
by a flip-flop during the preceding
Cylinder Out Upper and is also gated
in at this time.)
8. After one microsecond, DC~l returns to
its untriggered state to trigger
DC~2
for one microsecond. This causes the
following:
a. Data parity is checked. If not odd,
bit 20 ·of DSl is set along with DLI
Fault.
83318200 A
b. Seek Enable comes up. If the com-
mand is a seek (SFL, SRL, or RCB),
it is executed at this time.
c. SRI Out FF clears to drop SRI.
On an input command (Cylinder In Lower in
Figure 3-18), Serial Write Out is raised in
response to Serial Read In, Execution se-
quence is as follows:
1. Command byte raised by controller.
2. Drive decodes command as Cylinder In
Lower (100 011). This gates the con-
tents of the Cylinder Address Register
(Figure 3-17) onto the multiplexer.
3. Device Command Strobe is raised by the
controller, triggering single-shot
OCg3 for 500 nanoseconds. The multi-
plexer data is loaded into the Data
Buffer which serves both channels.
4. The data is immediately applied to the
I/O transmitters
(and
also to the re-
ceivers).
5. If both
DCO
and DCl are not down, the
drive will add a parity bit (DIP) if
required. Correct parity is not, how-
ever, checked.
6.
After
DC~3 t~es
out, it triggers sin-
gle-shot DC~4 for 500 nanoseconds. When
it times out, SRI In
FF
sets to raise
Serial Read In to the controller.
7. When the controller raises Serial Write
Out, Serial Read In, SRI drops.
8.
When the controller drops Device Com-
mand Strobe, the Data Buffer is reset.
Read or Write operations have a similar, but
not identical, Serial Read In/Serial Write
Out exchange. Refer to the applicable
~ry.
discussion for further information.
For commands where data is not exchanged
(Control Commands), the bidirectional data
lines are not sampled for data or parity.
SEEK OPERATIONS
GENERAL
Seek operations are those drive functions
that cause a repositioning of the read/write
heads. The heads are attached to the actu-
ator which in turn, is moved in a voice coil
positioner. The mechanical elements involved
in the mechanism are described in the
as~ly
portion of subsection lAo
3-41