IBM 3274 51C Maintenance Information page 260

F.2.3 Typical Device Operation
Figure F-13 shows the sequence of diskette operation.
1. The host system starts the diskette drive motor.
2. The operator inserts a diskette and turns the operator
knob to the closed position. With the operator knob in
the closed position, the diskette starts turning, and the
read/write"heads move into position on the diskette sur-
face (see F.2.2) for mechanical operation).
3. Index pulses are sensed every revolution (166.7 ms).
The type of "diskette inserted is identified on the diskette
Sense line. An up level indicates a diskette 2 or 20 while
a down level indicates a diskette 1.
4. The using system sequentially activates the two access
lines to move the head/carriage assembly in (toward the
hub) or out (away from the h~b) to select the desired
cylinder. Then the system sequentially activates the
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J-l.5
ms to 3.0 ms
Index
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.
1
1
Head Engagged
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Read/Write Operation
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~
Access 0
, I
Access 1
\ i
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10
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,
access line to turn the stepper motor a distance equal
to one cylinder. The two access lines last used to move
the head/carriage to the desired cylinder remain active
Q.
Data from the selected cylinder is valid after
40 ms (minimum time for the head and carriage assem-
bly to stop).
5. A head load command can be given before or during a
seek to activate the head load solenoid. Data is valid
80 ms after the heads are loaded. Address bytes of the
first available 10 (identifier) field are read, which verify
that the heads are in the correct position.
6. Reading or writing can occur 40 ms after seeking to the
last cylinder" ' or 80 ms after the heads are loaded.
7. The read/write head is unloaded after the read or write
operation.
166.7 ms
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•
,
\
80 ms Minimum
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40 ms Minimum
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'0'
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2
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3
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Cylinder 0
~~~-'f4
Cylinder 5 ~
~
5 ms Cylinder-to-Cylinder Seek Time
Note: Seeking and head loading are not to the index.
Figure F-13. Diskette Operation Sequence
F-16