also still thinks that items of the genus computer were designed to fit together
The really BIG error was, of course, in the literature. Not once did any of
the manuals state that the D-DOS software was written for a N-2 and that it would
only work on a N-1 if (and only if) the N-1 was running at 4MHz, all you’d get at
2MHz would be a clunk, a wheerr (if you get my meaning) and a system crash. [Ed. – We
can think of no reason why D-DOS/G805 shouldn’t be run at 2MHz. Perhaps your Nascom
clock is running very slow, as below about 1.85MHz the software loop isn’t fast
enough to get the data.] This fact took me a couple of hours of grief and worry,
while standing ankle deep in bits of my favourite computer, to find out (not to
mention a peak rate telephone call to EV Computing in Manchester).
When the thing was running ‘right proper like’ another problem raised its
head (as usual). The original address of the D-DOS software is B000H which messes up
the memory map of a 48K machine (brag, brag) very nicely. To overcome this problem I
moved D-DOS up to D000H. After disassembling the first 1K of D-DOS by hand, I came up
with the following –
From the above, I think you can see that the only thing you need do to D-DOS
to move it to another memory location is to alter the addresses of all the JUMPS and
subroutine CALLS to the new address. For example, to run D-DOS at D000 change all the
jump and call addresses from BXXX to DXXX. To access a disk under Nas-Sys 3, all I
have to do is type ‘D’ and ‘NL’ and I’m straight into D-DOS.
Also of some minor interest is the fact that D-DOS is no longer in EPROM but
in a 2K block of non-volatile RAM which is write protected and it seems happy there!
D.G. Richards of Glamorgan, $.Wales
AND FINALLY, THANKS.
Many thanks for a fine magazine – it was the quality of this, with all its
information on hardware etc that finally persuaded me to purchase a Nascom 2. Even if
I hadn’t bought a Nascom it is worth buying the mag. for the ‘Teach Yourself Z80’
series alone – many thanks to Dave Hunt. [Ed. – Spare the blushes Dave, I haven’t
published the letter that slates you something rotten!] It took me quite a few
readings to understand B2HEX, but I finally got the jist of it. I then found that in
my Nas-Sys 1 the routine was different (but much easier to work out). I even plucked
up courage to single step thro’ the routine, and then wished I hadn’t – it was only a
few days later that I came across the fact that certain Nas-Sys routines cannot be
single stepped! Anyway, I am still looking forward to the rest of the series. [Ed. –
Finally, are there any other readers in the King’s Lynn area who would like
to make contact?
Paul Tostevin, _ ______ ___, King’s Lynn, Norfolk, ____ ___. Tel. ____.
EDITOR’S NOTE – Letters are very welcome on any Nascom/Gemini related topic and the
author of any letter published will receive £3. We also would very much like to hear
from you about any computer clubs which have been set up, or which are in the process
of being formed. Perhaps representatives of the various clubs could write giving
details of their meetings and activities as their are probably lots of potential
members reading this.