Utters from the gutters By Mick Waters
Before getting down to the meaty bits, I should say that I am one of Dr.
Dark’s dodos in that I have never before submitted anything for publication.
In the past I haven’t subscribed regularly to either the INMC or 80-BUS News
and used to pick up my copies about once a year on my rare excursions to one
of the London dealers. This year I made a resolution to persuade (con) a
relative into buying me a subscription as a Christmas present and so now I
should be able to read the latest scandal almost as it happens. I don’t
pretend to be an authority on Nascom hardware but have managed over the past
five years or so to become reasonably acquainted with the way they work. Mind
you, being an RAF technician, I am an expert on modern electronic techniques
(circa 1960) and can write volumes on pentodes, triodes and other glass
encapsulated transistors with heaters. Since I have been about 12 months
behind everyone else, this article may be too late for solving the problems of
a couple of readers who asked for advice as far back as the March/April 83
issue but here goes regardless.
The first problem(s) of interest came from S. Willmott and from the
Sept/Oct 83 issue of Dr. Darks diary. First Dr. Dark, your problem with SIMON
getting in the way when verifying a page-mode style RAM-DISK appears to me to
be due to the fact that the Nascom computers do not support page mode and
SIMON will be present (and generating a RAMDIS signal) no matter what page of
RAM is selected. The answer? Read on.
Mr Willmott asked how SIMON may be removed from the system once its job
is done. I did (yet) another mod to my N2 as I objected to losing 4k of RAM
and also to the prospect of buying a page mode EPROM board for one chip. My
solution is not very elegant but it works. Below is a table of advantages and
disadvantages which should be weighed up before going any further:
For it Against it
1. . Its CHEAP. (Free in fact) 1. The tape drive may. no longer
2. It doesn’t involve hacking your be used for anything else.
faithful Nascom around. 2. SIMON doesn’t work apart from
3. It works. booting the system up as it
effectively switches itself out.
3. You must power up with a disk in
4. Pressing RESET doesn’t work any
more. The only way to reset is to
switch off then switch back on.
This creates problems when a
program goes into a loop as you
can’t then RESET and examine the
5. This mod. may only be used
if an IVC is fitted as chips are
borrowed from the redundant
Nascom video circuitry.
In my opinion, the advantages outweigh the disadvantages, you may not
think so. If you decide to try this mod, proceed as follows:
1. Pull out the chips used for the video circuitry except IC8.
2. On LKSI remove all links except for the link between pins 3 and 14.