80-Bus News


April–June 1982, Volume 1, Issue 2

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also still thinks that items of the genus computer were designed to fit together effortlessly.

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. [Ra. – We can think of no reason why D-DOS/G805 shouldn’t be run at 2MHz. Perhaps your Nascom cloek 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 T moved D-DOS up to D000H. After disassembling the first 1K of D-DOS by hand, I came up with the following –

B000 C300B4 BO10 C370B2 BO13 C3A5B2 BO16 C331B0 BO19 C3DAB2 BO1C C3A1B3 BO1F C373B1 BO22 C304B2 BO25 C339B2 BO28 C324B1 BO2E C307B1 BOSF CDO7BI1 BO42 CDE3BO BO4C C24BBO BO53 CDC4BO BOGF CD60BO BO7E CD57BO BO86 CD60B0 BO95 CD57BO BO9D CD57BO BOB3 CD57BO

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


i) an tse St Sa me

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 WNascom it is worth buying the mag. for the ‘Teach Yourself Z80’ series alone – many thanks to Dave Hunt. [Ea. – 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 Poort | stepped! Anyway, I am still looking forward to the rest of the series. [Bd. – Fool!

Finally, are there any other readers in the King’s Lynn area who would like to make contact?

Paul Tostevin, 8 Sidney St., King’s Lynn, Norfolk, PE3O 5RH. Tel. 5174.

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.

This is an OCR’d version of the scanned page and likely contains recognition errors.

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