We’ve received the following from John Fisher of Ipswich who
very kindly sent us a tape which we took to be a Naspen tape. It
wasn’t! We presume the tape was made on a text handler of his own, and
the tape format was ASCII strings, more like a Basic LIST. Still
about 5 minutes of thinking had tape loader software prepared, and the
following into a Naspen file for editing...
HOMEBREW HARDWARE by John Fisher.
This is the first of a (possible) series of notes for enhancing
the performance of the NASCOM-2. The author’s interests are to do with
pictures and signal processing and to this end I have tried to increase
the speed and memory capacity of the processor, to [increase the speed
of the cassette interface and to develop a cheap and flexible way of
drawing pictures. These requirements happen to co-incide with those of
First of ail the memory.
This expands the memory of the ‘32k’ RAM (A) board from 32k
(which it has already got sockets for) up to 48k. This is accomplished
by connecting a further eight dynamic RAM memory chips onto. the
multiplexed address bus internal to the board. This means that only 2
additional ICs apart from the 4116s are needed and very little extra
wiring need be done, such that it can be done in an afternoon.
Here is a step-by-step list of the modifications needed.
1) Connect the 8 extra 4116s piggy-backed on top of [Cs 12-19,
(see diagram) with all pins paralleled except the pin 4s. (Row
Address Strobe). 1! used sockets soldered to the backs of the
existing 4116s with the pin 4s bent up.
2) Connect atl 8 of the new pin 4s together. This is the new
3) Wire up a new RAS3 driving circuit as follows:
Create a new address select pad P99. connect this to +5v via a
1k resistor ()
Mount 2 extra ICs (38 & 39). These are 74LS02 and 7432
respectively. This can be done by a small strip of Veroboard
and some doublesided Sellotape. I put the chips on top of
positions IC 29 & IC 30. ()
CUT the following tracks on the p.c.
Ic Pin to IC Pin
36 «14 +5v 36 13 ( )
37 8 36 2 ()
CONNECT the following:
IC Pin to Ic Pin ()
– P99 36 13 ()
37 8 39 1 C)
39 3 36 2 ()
– P99 38 5 ()