INMC 80 News


September 1980 – January 1981, Issue 2

Page 22 of 59

Kbd mods

Mods For Demon Typists

by Derek Brough

Having, for the umpteenth time, cursed the lack of a left hand shift key on the N1 keyboard, I decided to do something about it. The mods were quite simple even though I only possessed two hands, and whats more it worked (second time) much to my surprise.

First the theory – briefly the keyboard works by having an 8 x 6 matrix of keys with eight driver wires which are pulsed in sequence under software control. Six wires sense which key (if any) is depressed (ready to prescribe some Valium no doubt). To fit a second parallel shift key we must wire the new key in series with both the drive and sense wires of the existing shift key. The wires must also be connected with the correct polarity otherwise the sensed pulse will be upside down (which is why my first attempt didn’t work).

Now for the painting by numbers:

  1. Obtain the spare Licon key and blank keytop (price 1.20 (I think) from Interface Components, Amersham).
  2. Look at the underside of the keyboard pcb, placed with the space bar to the top. It will look something like diagram 1. (I have added the letters to, the drawing. The capital letters refer to the key pins, the small letters to the tracks.)
  3. Carefully drill 4 1mm holes immediately to the left of the ‘Z’ key, on the same horizontal line. Dimesions as per diagram 2.
  4. The right hand hole will be too close to track ‘p’ for comfort so cut out a small section of this track with a sharp knife and replace it with thin insulated wire to avoid pin ‘C’, diagram 3.
  5. Cut tracks ‘a’ and ‘b’ near pins ‘A’ and ‘B’.
  6. Connect pin ‘B’ to pin ‘E’.
  7. Connect pin ‘E’ to the free end of track ‘b’.
  8. Connect pin ‘A’ to pin ‘C’ and pin ‘D’ to the free end of track ‘a’. These two wires should be lightly twisted together to reduce noise. If you have done it all correctly, the new shift key should work.

Ed. Please note that Nascom keyboards carry a one year guarantee from Licon, which is nothing to do with Nascom. The above modifications will void the keyboard guarantee.


Correction : I/O Board Review

In the review of the Nascom I/O board in INMC 80-1 (the last issue), it was stated that the UART did not have the ability to send and receive simultaneously at different speeds. This was incorrect. The UART speed select links allow different send and recieve speeds to be used. This was an oversight on the part of the reviewer, for which, we apologise.

Nascom have also pointed out the despite our INMC award for incomprehensible documentation, no complaints have been received. (Yet !!)

Page 22 of 59