INMC 80 News


May–September 1981 · Issue 4

Page 33 of 71

Dr. D’s Diary

Episode the Ninth.

  (Can’t think of a better name for it, unfortunately, so that will have to do.)

Big decision time

As I probably neglected to mention, I recently added a Cottis-Blandford cassette interface to Marvin (for the benefit of new readers, this means “my Nascom 1”). With great care, I designed a method whereby both the old and the new tape systems could be used “at the touch of a button” (1 point for that one!) It didn’t work. Only the new system would work.

Situations such as these separate the good tapes from the bad. Suddenly, instead of having to sit and convert the tapes to the new system, I was faced with the horror of having to re-type anything that I wanted to use in the future. These are the moments, Nasfans, when deep thought has to come into play. (I mean, am I going to be prosecuted by the Receiver for using the expression “Nasfans”? ) Think long and hard about the priority you would give to Star Trek (I chose it) or some boring simulation of the British economy, converted from a program for the TRS80, pinched from Personal Computer World (who once took six months to fail to decide whether or not to print an extremely dull article of mine), and you will probably reach the same conclusions about what constitutes a worthwhile program as I did. The first thing to go in was my assembler. This was closely followed by the amazing graphics utility I use with Nascom BASIC, in order to get it to do fast graphics. (That is enough of the advertising, thanks – Ed) (That was not me – Real Ed.) Then Star Trek, of course. But, after those had gone in, and I had reached new levels of typing skill and boredom, there came a process of decision. And I can honestly say that I don’t really miss the programs that are lost. Not at all. Well, actually, I miss Lollipop Lady, the most truly original computer game I have seen yet…

Ongoing hardware situation.

Yet another board has been added to the fabulous Marvin’s motherboard. This time, it is a Winchester Technology WT910 sound board. (Actually, this is only one of the two boards I have added, of which more in a moment or two.)

The board has been widely advertised, so you don’t need me to tell you too much about what it can do, do you? Oh, all right then, but only because I’m paid by the page. (This is an outright lie – Ed.) The board appears to the processor to be sixteen memory locations that you can only write to. One of the reasons you can’t read them is that, presumably to avoid interfering with other RAM locations, they are at the same part of the memory map as the monitor. It is possible to “move” the board to the top of the memory map if you happen to have a disc based system, by changing one integrated circuit. This just happens to be a cheap one, which is not the usual thing, in circumstances such as these!

These sixteen “memory locations” are the control registers of an AY-3-8910 chip, which is pretty well the Rolls Royce (or, to put it another way, the Nascom) of the “sound synthesiser on a chip” world. It has three separate tone generators, each of which can be independantly controlled as regards volume, frequency, presence or absence of white noise. Automatic envelope shaping of the output is available, and this can provide fascinating rhythmic effects. At least, I find them fascinating! Several optional enhancements are available: sound modulator to make the sound come out of your TV, digital to analogue converter (so you can design wave shapes of your own, all you machine code addicts) and an amazing dedicated (well, it seems enthusiastic, at the very least!) microprocessor. The latter has been mask programmed with the first few notes of several well known tunes, and is the kind of gimmick I find quite hard to resist. In fact, I didn’t resist, so that every time I switch Marvin on, he produces an impression of Westminster chimes that makes the dog think there is someone at the door.

The quality of the board is superb, the documentation tells you all you need to know, and the price is probably reasonable, if you are not the sort of person who enjoys hand carving his/​her own circuit boards from the virgin copper laminate. But, if you are that sort of person, then read on......

Page 33 of 71