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Theory of Operation 2-7
During the write operation, the selected drive must have head-load, head select, write
enable and write data signals. During the read operation, the selected drive will perform a
head load. The write enable line remaining high implies a read operation. Under these
conditions the drive will transfer read data to the controller. Controller step and direction
commands are received initiating a track-seek operation on a selected drive. The selected
drive transmits a track 00 signal to the controller whenever the read/write heads are at track
00.
Positioning the carriage-mounted read/write heads is accomplished by a band-driven step-
per motor. Each step command from the user system increments the stepper motor which,
in turn, moves the band. The band increments the read/write heads one track for each step
command.
A read or write operation begins by placing the read/write heads in contact with the disc
with a Head-Load command at the desired track. To write on the disc, write enable is sent
by the controller to condition the write logic. The write current then in the head reverses
polarity synchronous with the high-to-low transitions of the write-data pulses from the
controller. The current reversals cause magnetic flux reversals on the desired disc track.
Erasure of previously recorded data is simultaneously accomplished during the writing
operation in addition to a delayed tunnel erase which ensures disc interchangeability.
To read from the disc, magnetized bits in the format of the pre-recorded data are sensed by
the read/write heads. This signal is amplified, digitized and transmitted to the controller.
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