The Signetics 2650 - The MESSUI Place

A training system from
Signetics: Instructor 50
Described by Signetics as a "desktop computer", the Instructor 50
has been designed primarily as a training tool. It offers a number of
features not found on small evaluation systems, and comes complete
with both a comprehensive set of training manuals and a tape
cassette loaded with eight demonstration programs.
by JAMIESON ROWE
Since 1976 when microprocessors
really began to " take off", many small
microcomputer systems using them
have appeared on the market. Some of
these have been intended for the hobbyist,
while others have been
"evaluation" kits or systems intended
to help engineers become familiar with
the particular microprocessor concerned.
But very few systems have been
designed._ specifically for training and
educationalpurposes. This is a pity,
because the concepts involved in
microcomputer operation are relatively
unfamiliar to many of the people who
are going to have to operate them,
program them, design them into equipment
or service equipment which will
use them.
Until now, those wanting to become
familiar with microcomputer concepts
have generally had to get hold of a
small hobby or evaluation system, and
largely use it to teach themselves by experience.
Most such systems have been
rather poorly supported by user
literature, particularly when it comes to
the introduction to basic concepts.
The Signetics "Instructor 50" system
is an attempt to fill this very gap. It is a
small desktop unit designed specifically
for training, and comes complete with a
comprehensive set of training manuals.
Also supplied as part of the training
package is a cassette tape with eight
demonstration programs, ready to feed
into the system via a standard cassette
recorder.
Superficially the har aware side of the
Instructor 50 looks rather like many of
the small evaluation systems, except
that it comes as a small cabinet rather
than a naked PC board. It has a hexadecimal
data input keyboard and an
eight digit 7-segment LED display, with
a separate 12-key pad for feeding in
commands to the monitor program.
Like some of the evaluation systems it
has an inbuilt cassette tape interface,
which will operate with any normal
92 ELECTRONICS Australia, May, 1979
audio cassette recorder. However unlike
the majority of evaluation systems
it also has full buffering and decoding
for system expansion using the S-100
bus convention — a feature which will
no doubt make it of interest to hob-
Neatly housed in a small desk-top case, the Instructor 50 system comes complete
with three comprehensive training manuals.
byists and small business users.
As you might expect, the Instructor
50 is based on the Signetics 2650
microprocessor. Along with the 2650 it
has 512 bytes of RAM for user programs
and a 2656 SMI (system memory interface)
device which contains a 2K byte
monitor program in ROM, together
with 128 bytes of RAM for the monitor
scratchpad.
The monitor program built into the
SMI is rather more powerful than is
usually found in evaluation systems.
Besides the usual facilities for entering
program instructions and data, examining
memory and processor registers,
and running programs, it offers a
number of features which make the
Instructor 50 easier and more straightforward
to use.
For example there is a "fast patch"
data entry mode, which allows instruction
and data bytes to be loaded into
memory rather faster and more conveniently
than the normal "display and
alter" mode. There is also a single-step
run mode, in which you can step
through programs instruction by instruction,
and a breakpoint facility
which enables you to exit from a
program at any desired point with the
processor's status preserved so that you
can analyse what had happened to that
point.
The monitor commands concerned'
with the cassette interface are also
more powerful than is usual. The "write
cassette" command used to dump a
program or data block to tape allows
the block to be given a file identification
number (from 00 to FF hex), while
the "read cassette" command may be
used to seek and load either a specified
file, or the first file encountered. There
is also an "adjust cassette" command,
in which the Instructor 50 can be used
to indicate the optimum playback level
for the cassette tape machine.
In short, then, the Instructor 50
hardware seems to have been designed
with particular emphasis on flexibility
and convenience of use -- making it