The Signetics 2650 - The MESSUI Place

GETTING INTO MICROPROCESSORS
teleprinter to develop small 2650
programs in machine language. They
could also be expanded into quite pretentious
minicomputer systems, by
adding further memory and IOT facilities.
An add-on RAM memory board is in
fact available, and is directly compatible
with either kit. Designated the PC2000,
it provides an additional 4k bytes of
memory.
At the time of writing this article, we
have only had the opportunity to
examine and use one of the PC1001
evaluation kits. This is on a PC board
measuring 203 x 175mm, with a 100-way
double sided edge connector along one
of the longer sides. The PC board is
pictured, and as you can see there are
quite a few IC's apart from the microprocessor.
In fact the PC board is a three-layer
assembly, with copper conductors sandwiched
in between two layers of epoxyfibreglass
as well as on the two external
surfaces. This has allowed Signetics to fit
a surprisingly large amount of circuitry on
the relatively modest PCB area.
On the PC1001 board is 1k bytes of
RAM, capable of storing quite a respectable
user program. In addition there is
another 1k bytes of ROM, containing a
resident monitor-debug program which
Signetics have dubbed "PIPBUG". This
will be described shortly.
There is an on-board serial asynchronous
teleprinter interface, which
may be adjusted by means of wire links
for either 20mA current loop interfacing
or RS232-type voltage interface.
In addition to the teleprinter interface
there are four 8-bit parallel IOT ports—
two inputs and two outputs. These are
wired to be accessed via the two-byte
"non-extended" IOT instructions, so that
small systems with four or less
peripherals (apart from the teleprinter)
may be implemented with no further
hardware.
The PC1001 board has a 1MHz crystal
clock, and therefore is immediately compatible
with a 110-baud teleprinter (serial
formatting is done by firmware routines,
so baud timing is derived from the system
clock).
Full data and address bus buffering is
provided on the PC1001 board, to simplify
addition of further memory or
peripherals. All of the control signals are
also available at the edge connector in
buffered form, which again simplifies any
required interfacing.
Although at the time of writing we
have not had the opportunity to examine
and use the PC1500/KT9500 evaluation
kit, we understand that this is based on
a PC board identical in size to that of the
PC1001, And although the second kit is
nominally a less pretentious one, it still
offers quite impressive facilities.
For example it still provides 1k bytes
1111•111111111116. AIR