80-Bus News


November–December 1983, Volume 2, Issue 6

Page 53 of 67

When using acoustic (or direct connected) 300 BAUD modems with Prestel, there have to be snags of course, firstly, the 300 BAUD service is restricted to only one computer, with a limited number of ports for its modems. This means that it is often engaged during the day, but evenings are a different story. I’ve no way of knowing, but I would guess that out of business hours, the 300 BAUD service is the quietest of the lot on the grounds that no-one knows it’s there. Another nasty is that BT don’t offer preferential rates for that number. If you live outside London, then dialing that number will get charged at trunk call rates, worse, because the data rate is one quarter of the normal Prestel data rate, everything takes four times as long to receive. The last flaw in the scheme is gaining access to Prestel, you require an individual access code which is many characters long. I’m not saying how many characters, just in case someone tries a bit of code cracking and hits my code by sheer good/​bad luck; mind you that could be expensive, because if you get the access code wrong a couple of times, Prestel tells you you are an idiot, and disconnects the line. You get your access code when you apply for the Prestel service. They ask you what device you intend to use. You reply, “Personal computer”. They ask you what. You say, “BBC”, or “Spectrum”, or “Oric” or some other approved device depending upon the computer you are using, or if you are using a 300 BAUD modem, you must make sure you get logged onto the Kipling computer, then you say “300 BAUD modem.”. Typically the person taking the logging details knows nothing about the 300 BAUD service so you’ll have to tell them. After a while, you get your access code, and given suitable software, away you go.

Now to suitable software, I’m writing a bit to make the Climax card look like a Prestel display, ’cos it’s got colour and all that. But David Parkinson’s dumb terminal routine works well enough to extract textual data and Ward Christenssen’s MODEM 7 works well for textual data with the advantage that you can store the incoming data and use it for testing Climax colour routines, etc. If you’ve got a Winchester Technology colour card collecting dust, you’re laughing, just plug it in and with the simplest of dumb terminal type software, you’re away.

Apart from Prestel with Micronet, which costs, there are a lot of telephone numbers with modems and active computers on the end. There are billboards, companies advertising, all sorts of things, most of which allow access for nothing. A whole bunch were published in PCW a couple of months back and some of these can provide hours of endless fun (providing someone else is paying the phone bill). One person I know tried the Swedish number published, hoping that the Swedes with their liberated views had something interesting to say. Unfortunately the computer replied in Swedish, so he’s none the wiser.

HDLC and Packet Radio

On the subject of serial communucations, I have recently come across references to a subject called ‘Packet Radio’ which has raised some interest in the States. On first reading this was pretty meaningless due to the sketchy nature of the odd paragraphs that appeared over here. However, Practical Wireless has seen fit to reprint the whole of one American explanatory article, and with a sigh (Oh no, not another protocol!), I sat down to read it. Now it turns out that ‘Packet Radio’ is not ‘just another protocol’, but a radio adaptation of an old enemy, HDLC. Now I say old enemy, as not so long ago one of the 80BUS board manufacturers asked me to look into high speed synchronous serial communications, in other words, making micros talk to

Page 53 of 67