8-Bit Software Online Conversion

MY EARLY DAYS WITH COMPUTERS By Robin Morom (K4R) Part 2 Those who have read Part 1 will know that in October, 1979 I had at last obtained a computer, the UK101, in kit form. "Now," as they say, "read on." The single PCB was very well made, with plated-through holes, considered the state of the art in those days. The keyboard and the voltage regulator were on the same board, with only the mains transformer as a separate item. 4k of RAM was included in the price and as the chips (2114) were only 1k by 4-bit it needed 8 chips just for the minimum. There was room for a further 4k on board but I made do for the time being. An extra 8 chips would cost £49.00 and may I remind you of the inflation since then. It seemed a great deal of money in those days. I stayed up half the night and got the thing assembled. Inspect for dry joints - switch on hopefully - no joy - switch off - check again - find one dry joint and two solder 'bridges' - switch on again - looks good - retune mono TV to find display - great, screen says ' D/C/W/M '. It seems absolutely nothing today but this was the first writing I had seen on the screen that was not part of a TV programme. A wonderful moment! Right, now read the manual. 'Press C for cold start.' OK, done that. Screen says MEMORY SIZE? Manual says 'Press RETURN for default' OK, done that. PANIC!! Screen says '252 BYTES FREE'. Should say 3324 BYTES i.e. 4k minus RAM claimed by operating system. Switch off again and think - re-examine RAM and find one chip with a pin bent under - correct this - switch on - this time 3324 BYTES - good. Next step...... And so on and so on. Eventually I got it working as it was meant to and was delighted with it. There was a cassette tape supplied which had two games and the manual had a few simple Basic programs. As the Basic was 8k Microsoft (in four separate chips in the original version) it had no proper graphics, colour or sound commands but it did have string handling such as MID$, LEFT$, RIGHT$ etc. LET was optional, rather unusual at the time and PRINT could be abbreviated as ? Of course, like all these things, I wanted to do more. Could I use the computer to run a model railway, and how about controlling the organ which I mentioned in part one? Was there any limit? Talking about the Maplin organ, I said last time that it was a kit. This was a slip of the keyboard. I should have said that it was a detailed design with many options and all the parts available separately from Maplin. Also while on the subject, I might as well admit that I must have had delusions of grandeur over that project. It was not until I had built it, or enough for it to be heard, that it slowly dawned on me that, despite being a fan of the cinema organ, not only could I not read a note of music but neither could I play ANY musical instrument! I bought several books of the 'Teach Yourself' variety and started to learn. And then it was practice, practice, practice. Eventually I got so good that the neighbours would come round and break the windows so that they could hear me better. Well, what I lacked in musical skill I made up for in VOLUME. To get back to the computer. There is nothing like having an uncased board in front of one to encourage hardware modifications. The most obvious thing was the arrangement of the <RESET> keys. There were TWO of these, wired in series, the idea being to prevent accidental resets. Stupidly, however the two keys were alongside each other and dangerously close to the <RETURN> key. It was very easy to press BOTH. I soon removed one of them to the other end of the keyboard, next to the <Q>, which meant that it needed two hands to do a reset. I sometimes think this should have been done to the <BREAK> key on the BBC. Next mod was automatic reset when switching on. Now it is no hassle to do a reset manually, but how much nicer to have it done for you by the computer. A couple of components and it's done. On studying the circuits, it was obvious that there were several spare gates on the TTL chips. They must be useful for something. One toggle switch and a couple of cuts in the PCB tracks and it was possible to have inverse video (black-on-white instead of white-on-black) as an option. By about Easter, 1980 there were plenty of UK101s and Superboards about and everyone was coming up with suggestions for improvements. 16 lines on the screen is not very many and since the screen was memory mapped into 1k it seemed likely that a further 1k would provide another 16 lines if the decoding and the software could cope. There was actually no space on the board so the additional screen memory chips had to be piggy-backed on to the existing ones. A little extra decoding and some juggling with the clocks plus another toggle switch and there it was - 16 or 32 lines as required. It had to be switched since not all programs were suitable for both. Talking of clocks, the 6502 microprocessor was intended to run at 1Mhz but it was possible to run many of them at 2Mhz. I was lucky, mine did. Double calculating speed on demand! Yet another toggle switch and it was an option. It was very important NOT to try and change this while running a program. The computer would usually crash and need a cold reset. Now I come to what I suspect may be the most surprising thing to many members. I have come across very few people who have even heard of it. The cassette loading on the UK101 was interesting because everything was written to the screen as it loaded so that any garbage was obvious and you could rewind a line or two and try again. The rate was 300 baud. Having nothing to compare it with I did not realise how slow this was but you can try it on the BBC or Master using *TAPE3. The BBC default is of course 1200 baud. There were no options for baud rate built into the UK101 but the clocks were very accessible so I tried doubling the rate to 600 baud. It worked but was a little touchy to load. The trouble with higher baud rates on cassette is that you are recording onto an analogue device. The recorded pulses get 'rounded' and are likely to be misread on reloading. Then I read about a new circuit available as an add-on board. This was the Cottis Blandford interface. This was brilliant! Originally intended for the Nascom computer, it cost £14 or thereabouts and its purpose was to clean up the pulses when saving and then reclean them on loading. It was then possible to use a higher baud rate. When connected it performed beautifully. Being very cautious I first tried it at the original rate. Perfect. Now 600 baud. No problem. 1200? Yes. Try 2400? YES. The instructions said that higher rates 'might be possible'. Well, no harm in trying 4800. It still worked! Up to now I had been using a very cheap cassette recorder and the C12 cassettes which were sold for computing use. I tried 9600 baud and was hardly surprised to have some difficulty. However, when I used a high quality cassette deck even this rate worked with only the very occasional problem. I even used 19200 baud with my broadcast-quality reel-to-reel recorder but this was more trouble than it was worth. For one thing it took very much longer to locate the program than to load it! This was at 16 times the rate which Acorn subsequently used for the BBC! So why didn't they use something similar? Presumably because they wanted to eventually sell disc systems and be able to emphasise the difference. 19.2k was about the same loading rate as the then 'standard' i.e. 8-inch discs. (5-inch discs were 'mini-floppies') Perhaps I should add for the experts reading this that I admit having greatly simplified my explanation. (Yes, there were problems in timing and getting the right number of nulls, etc.) Eventually I added lots more to the UK101 such as a memory expansion which got me up to 24K, a PIA and A/D chip so that I could use a joystick, etc. There were colour boards available (at a price!), disc controllers and sound boards in the course of time, but by then I was ready to move on. NEXT TIME: a look at a few of the many machines which began to appear in the early eighties.