Functional Description; Control Logic - Control Data Corporation BR8 SERIES Hardware Maintenance Manual

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A reading or writing operation begins by placing the Read/Write head in contact with the
disk with a Head Load command and at the desired track. To write on the disk, Write
Enable is sent by the controller to condition the write logic. The write current then
in the head, reverses polarity synchronous with the low-to-high transitions of the
Write Data pulses from the controller. The current reversals cause magnetic flux
reversals, the data and clock bits which are induced on the desired disk track. Erasure
of previously recorded data is simultaneously accomplished during the writing operation
in addition to a delayed-tunnel-erase which ensures disk interchangeability.
To read from the disk, magnetized bits in the format of the pre-recorded data are
sensed by the read/write head. This signal is amplified, digitized, separated into
clock and data information, and transmitted 10 the user system.
4.3 FUNCTIONAL DESCRIPTION
Refer to Figures 4-1, 5-1, and the Schematic Diagram, Figure 5-2, for the following
discuss ion.
The FDD is divided into the following major functional areas:
a. Control Logic
b. Write and Fault Logic
c. Read Logic
d. Disk Drive
e. Read/Write Head
4.3.1 CONTROL LOGIC
The functions of the control logic are to generate the signals that (a) establish "the ready
status of the FDD,
(b)
step the Read/Write head in or out upon selection and command of
the controller, (c) load the head on the disk for read/write
operations~
(d) protect the
disk from writing if the write protect hole is present, (e) indicate when the Read/Write
head is at Track 00, (f) generate the index and sector pulses when the diskette is rotating
and the FDD is selected,
(g)
unlock the FDD door latch upon command of the controller
through one of four switch or jumper-selected control lines , and (h) unit selection
of the FDD.
a. The Ready signal is generated when the disk comes up to proper operating
speed. The in,dex pulses are used to re-trigger the multivibrator (U31 pin 5).
The output of this element will remain high on a continuous basis when the
repetition rate of the index pulses is shorter than the time out of U 31 pin 7.
This logic function is used to control the R/S flip flop (U19) to generate the"
Ready signal. W 33 or switches (5," 6, 7 and 8) allow selection of the relative
position of each FDD within the Daisy Chain Configuration.
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