are handled in software. These functions are normally called from the Nascom
Basic, using the SET function to allow the Basic functions to be extended. All
functions were treated in detail. One oddity was noticed, there was no circle
drawing function, but a function for drawing regular polygons with n sides was
provided, a 255 sided polygon was found to produce an entirely satisfactory
card, the Nascom card requires extensive software to
drive it and a disk or tape is supplied with a number of colour driver
primitives, the manual explains these are well, function for function. Sadly
Nascom do not see fit to supply the source listings of these colour driver
primitives. A pity as some of them are extremely fast and efficient. Without
the source it would be difficult to rewrite these to allow the card to be used
with systems not based around the the Nascom 8K Basic.
The Climax Card.
The manual supplied with the
falls midway between the Pluto and
Nascom manuals. Certainly fatter than the Pluto manual, it was single sided
photostated sheets with no binding. The manual started with the get you going
bit of how to connect the card, followed shortly by a simple Basic program to
test the correct working of the card. Just the sort of order I like things,
read a bit of the manual, plug it in and see if it goes!! This was followed by
a fairly good and certainly adequate description of the workings of the card,
but no circuit diagrams. The description was followed by a very well written
section on the uses of the registers of the Thompson chip. This is much more
understandable than the manufacturers descriptions I have read in their data
sheets. To finish the description of the registers a short extract of the
Thompson data sheet was supplied to clarify timing and register addressing. So
far so good.
As explained previously, the Thompson chip is capable of point to
point line drawing, plotting points, colour changing, and a lot of other
simple things (the chip has an internal character set for instance), however,
to do the cleverer things like drawing circles requires external software. The
manual follows the chip description with a description of the software drivers
and a complete source listing. Now when I comment source files for publication
in this rag, I often think to myself that the amount of comment included is
overkill. Climax seem to work on the same principle, the comment is certainly
extensive, and make the routines fully understandable. The colour driver
“primitives are intended to link automatically with MBASIC, but because they
are written entirely as subroutines, they can easily be modified into stand
alone machine code routines, or linked with some other high level language.
Whilst on the subject of the Climax driver routines, I must say they
had their drawbacks. The source listing is printed in the manual, but is also
available on disk with some demo material. The snag was that I didn’t have the
disk so I had to type in about 40K of source and then hope I had got it right.
That was 40K without much of the comment – when I finally did receive the
disk, I found the source listing was the best part of 100K. Still it was good
typing practice and even more incredible, I only made two mistakes.
USING THE CARDS.
The Pluto Card.
card was certainly fast and powerful. My main complaint with
the card was not with the card itself but with the documentation which as
mentioned previously, I found awkward. Fairly simple programs could be written
in Basic to provide the necessary primitives to draw lines etc, and line