INMC 80 News


February–April 1981, Issue 3

Page 16 of 55

32K→48K Expansion

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.


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 ‘dynamic‘ games.

First of all 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 ICs 12-19, (see diagram) with all pins paralleled except the pin 4s.​(Row Address Strobe). I used sockets soldered to the backs of the existing 4116s with the pin 4s bent up.
  2. Connect all 8 of the new pin 4s together. This is the new RAS3 point.
  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.

3614+5v3613(   )
378362(   )

CONNECT the following:

ICPintoICPin(   )
P993613(   )
378391(   )
393362(   )
P99385(   )

Page 16 of 55