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Chapter
2
Theory of Operation
Introduction
This chapter contains the
9895A
theory of operation and block diagrams. The
9895A
can be
broken down into a controller module, a drive module and a power supply. The controller is
described first, then the drive, followed by the power supply.
Controller Module Theory of Operation
Introduction
This section provides a functional description of the controller, part number
09895-66500.
General Description
The controller module provides an interface between a Hewlett-Packard Interface Bus
(HP-18) channel and up to four disc drives. Commands are accepted from the HP-IB
channel and interpreted to provide the proper operating sequences for the selected disc
drive. This includes:
•Providing control and timing signals,
•Sending data to the disc drive,
•Receiving data from the disc drive,
•Handling all input/ output communication with the drive channel.
The controller provides control signals to the drive and receives the resulting status informa-
tion.
If an error occurs, or when a disc is removed or inserted Into a disc drive, the controller
requests attention from the HP-18. It also generates and decodes error detection bits which
are recorded with the data. In addition to these normal operations, self-tests are performed
on the controller and the disc drives.
2-1
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