INMC 80 News

Next you install a single 2708 on the Nascom. Set the Reset Jump to F000H, switch on, insert a disk and hey presto, it works. Well mine worked straight away anyway. A friend of mine was not so lucky as he put the 2708 in the wrong way round and KILLED SIMON!! What’s SIMON – the 2708 of course, SImple MONitor.

SIMON is actually very clever for ‘his’ size. He lives at F000H and ‘boots’ up the disk. If there is no disk present, or a disk without a CP/M system installed is inserted, then control is passed to SIMON and an error message is output. SIMON also contains a keyboard routine, screen routine and several Nas-Sys like commands – Copy, Execute, Fill, Modify, Output, Query, Tabulate and Boot to load the CP/M once you decide what you did wrong last time. SIMON allows you to work out (hopefully) where the fault is should something fail. The other clever thing about SIMON is that he works out whether or not you have got the Gemini 80x25 video card, and uses it if it is there!

So now we are into CP/M, let’s read the CP/M manuals. This is where the fun and games begin. There are SEVEN manuals provided by Digital Research, the authors of CP/M, and these all come in the G513, PLUS a 23 page manual from Gemini on their actual implementation of the CP/M provided. Despairing at the look of the DR manuals you open the Gemini one and find it recommending yet another book! Zaks, to be precise, and this is in fact good advise. Why? Well the Digital Research manuals are concise and extremely useful once you have an idea of what you are doing, but as an introduction they are not very readable. On the other hand the Gemini manual is very readable, but limits itself to the BIOS implementation and the routines supplied by Gemini (a Format routine and a very useful Backup routine.) So to the CP/M beginner something like ‘The CP/M Handbook’ by Zaks should be obtained.

But what about the CP/M itself? Well several friends, owners of other unprintable systems, have had a good look at my Nascom and declared the Gemini CP/M implementation to be far better than their own (Tee Hee). Why? Well, for a start you get TWO CP/Ms for your money. One is set up for the ordinary Nascom memory mapped screen (now residing at F800H), and the other is set up for the Gemini 80x25 IVC (Intelligent Video Controller) card. You just choose the one you want, neat eh? When I started I used the Nascom screen and the relevant CP/M, then, when funds allowed, I bought the IVC and used the other CP/M (Ed. – the author also sent us a review of the Gemini G812 IVC, but we’re holding that for the next issue.) The Nascom screen driver also incorporates a number of the functions available on the IVC. These include Cursor addressing, Clear to end of line/​screen, plus another very useful feature. (See below.)

The CP/M BIOS also supports ‘Auto-density’ on any drive other than ‘A’. This means that drive A must have a Gemini double density format disk installed, but other drives may read or write disks in either double density or in the same single density format (SD Systems) as the G805/​Henelec, completely automatically. (Ed. There is a slight problem here, see elsewhere in this issue for the solution.) The FORMAT routine supplied allows either S or D density formatting. Also supplied is a BACKUP program that allows entire disks, including the system tracks, to be copied very quickly – even on a single drive system. This is much better than having to ‘PIP’ and ‘SYSGEN’.

There are several very useful features in the keyboard routine. Pressing ‘Control/​Enter’ toggles an ‘Upper Case Lock’, handy for assembler work and for running some CP/M programs that don’t seem to respond to lower cases. Another feature is ‘Control/​Backspace’ – this toggles the function of the () keys so that square brackets [] are returned instead. This is invaluable to the N1 keyboard owner who otherwise cannot use many of the options provided by certain CP/M utilities. And on the N2 keyboard the ‘CH’ acts as a ‘TAB’ key – very useful in CP/M editors.