Scor­pio News

Doctor Dark’s Diary – Episode 24

Just as I was about to start my own Nascom fanzine, duplicated badly, and printed on grotty paper, the leaflet advertising Scorpio News arrived. I was delighted to see it, and posted my subscription the same afternoon. After all, I suspect publishing is jolly hard work, and I bet this gets printed on decent quality paper as well. Besides, I would have needed the address list of the 80-BUS subscribers, and something to print…

THE STORY SO FAR

For the benefit of the many who have never heard of me, and have not read the previous 23 episodes of this column, now appearing in its third magazine, I am an enthusiastic amateur computer owner. I am enthusiastic because the machines we all have in common are so good, compared with the other stuff on the market. And I am an amateur because there don’t seem to be any computer firms with the sense to offer me a job in this neck of the woods.

I started out with a Nascom 1 kit, which amazed me by working after I had built it. I learned to program from the Nascom 1 software manual, which is no mean feat, as this document was designed to prevent people from wanting to use their Nascom 1s. By the time I had finished my machine code biorhythm program, and typed in the hex using the monitor progrogram, I was hopelessly hooked. As the various expensive new boards appeared, I expanded the machine, changing to a Nascom 2 when the Nascom 1 refused to run at 4MHz (I know, lots do. Mine wouldn’t). The system this is being written on consists of the following: Nascom 2, Nascom 8 amp power supply. Gemini G809 disc drive controller, two Pertec FD250 drives, a Pluto graphics board, a Gemini SVC , two MAP-80 256K RAM boards, a Gemini GM870 modem board, a Belectra floating point board, and a Nascom IO board. There are three screens, one for the Pluto, one for the SVC, and one for the Nascom 2 screen.

Languages in use are Z80 assembler whenever I want things to go particularly fast, Basic when they can go slowly, and nobody is going to know, Pascal when I am writing something large, with fancy data structures, and C when I am in the food for some suffering and can stand the ugliness of it. For instance, my current project, some Prestel software, is being written in assembler, in the hope that it will go fast enough not to need fancy queues of data of horrid interrupt driven software. I was originally going to write it in Hisoft Pascal, but changed my mind because I thought it might not go quite fast enough, and because I would have ad to plan everything properly. I decided against C for the simple reason that I don’t feel I know it fully yet (Has anyone seen a book that explains anonymous date types properly?) The reason I didn’t us BASIC, is that it would never run properly…

Now all that must sound (I hope) very competent and educated. Fooled you! We sixth form dropouts sometimes recover from thinking we can not learn new tricks, you see. In 1978 knew none of these things, but am now half way to an Open University degree, mostly in maths. One of these days, with the help of the escape committee, I hope to escape from my boring job and have some fun doing something interesting with micros. And that ie quite enough about me. Now read on…

Hard­ware Unpleasantmess Strikes!

As is well known, the Gemini GM870 MODEM board and the Belectra HSA-88B floating point board both use port addresses £80 and £81, so I can not use them both at once. In theory, it is possible to move a link on the HSA-88B, and have it work as other ports, but (again) mine won’t. I am planning to build some sort of decoder to select between the two boards, if there is no other cure, but not unless I have to.

The main reason I described interrupt routines as unpleasant above is that the last one I wrote, several tines, refuses to work. It tried to use the CTC chip on my Nascom I/O board to interrupt the system regularly, in order to read the MODEM’s input port, and queue up any input. However, the program just will not