S-100 EXPANSION for NASCOM 1
This is a shortened version of an article sent in by Mr. K. P,
Curtis of New Barnet. The INMC would very much like to hear from anyone
else who has expanded their Nascom via the S100 bus.
I decided to expand my Nascom 1 with a S100 expansion kit currently
being offered. Despite being more expensive in the short term, I felt
that it widened the choice available to further enhance my system.
The kit consisted of :–
1) A double sided PCB without plated through holes that will
accomodate three cards.
2) Two edge connectors and ribbon cable to connect the Nascom
to the expansion board.
3) All required 1C’s and sockets except one, a tri-state buffer
for control signals which is optional. (Would recommend this
is used ED.)
4) Lots of vero pins to make the through board connections.
5) Decoupling capacitors.
6) A 2K Basic interpreter (B-Basic).
The instruction for assembling the board are adequate but the
following points should be noted:
Insert all vero pins before soldering and very carefully check
their positions as it is very easy to get them in the wrong positions.
Some pins need to be cut short to allow sockets to sit flush on
The longest part of assembly was making up the ribbon cable
assembly – very tedious.
A circuit diagram of the logic is provided but does not match
the board layout and the logic that generates the MEMEXT signal,
although functionally the same, is misleading. Also only the pin
numbers of the buffers are given and some of the IC legends appear to
have been incorrectly printed on the board.
Beside these errors I found two connections not made in the
external I/O logic : IC5/15 to IC10/1 and IC9/11 to IC9/10.
The ready built 8K RAM card that is being used requires an 8V
unregulated supply from the S100 bus. This may be obtained from the
existing power supply – after the rectifier but before the dropper
resistors and regulator. Before attempting to use the kit and memory
though, the rating of the rectifier should be checked – mine lasted for