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General Information
The recording head in the drive module is positioned by a mechanism that includes a
stepper motor, capstan and taut metal band. The mechanism operates in an open loop
configuration, that is, there is no positive feedback to determine the actual position of the
head. The head assembly has two read/write heads, one for each side of the flexible disc.
When the heads are loaded, both contact the medium. The heads are automatically un-
loaded one and a half seconds after the last command is received.
The controller module contains a Micro CPU Chip (Z80), a processor-to-HP-IB Interface
(PHI) Chip, Read-Only Memory (ROM), Random Access Memory (RAM) and the associated
logic circuits necessary to provide an interface between up to four disc drive assemblies and
the HP-IB interface channel. The Z80 handles data and commands directly at the byte level.
The controller module also contains an extensive self-test capability. Self-test functions
include various combinations of read/write operations on numerous tracks. All self-test
functions may be initialized by manual switching or HP-IB command except a pre-formatted
read-only test, which is switch-initiated only. The controller module performs a subset of the
self-test each time power is applied. This subset does not include reading from or writing to a
disc. Self-test results are available as a four-bit binary word displayed on an LED array
mounted on the controller module or as two bytes of status information which can be read
by the host system.
The 9895A will read and write the HP standard flexible disc format as used on the HP 9885
Flexible Disc Drive, on either Single-sided or double-sided discs. The 9895A will also read
and write the IBM 128 bytes per sector standard data interchange format (IBM 3740) on a
single-sided disc. When a formatted disc is loaded into the disc drive, the controller module
will determine which format is being used and whether the disc is single- or double-sided.
Format and disc type are both reported as status information. When a disc is re-formatted,
the controller module performs defective track labeling and sparing as well as track re-
formatting.
Data transfers are buffered on a sector-to-sector basis. This allows devices connected to the
flexible disc memory to access data at any rate up to the maximum burst rate.
A modular replacement philosophy has been implemented in the flexible disc memory to
minimize on-site repair time. Troubleshooting the flexible disc memory is simplified by its
self-test diagnostics.
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