BBC Micro

23 Articles

Reading Floppies With An Oscilloscope

May 20, 2021 by 6 Comments

There’s a lot of data on magnetic media that will soon be lost forever, as floppies weren’t really made to sit in attics and basements for decades and still work. [Chris Evans] and [Phil Pemberton] needed to read some disks that reportedly contained source code for several BBC Micro games, including Repton 3. They turned to Greaseweazle, an interface board that can dump just about any kind of floppy disk if it is attached to the right drive. The problem is that Greaseweazle couldn’t read the disks due to CRC errors. Time to break out the oscilloscope and read the disk manually, which is what they did.

Greaseweazle provides a nice display of read sectors and shows timing coming from the floppy read head. The disk in question looked good with reasonably clean timing clocks except in the area of one sector. At that point, the clocks degenerated into noise. Looking on the disk, it was easy to see why. The actual media had a small dent in it.

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The Tube Map, In Glorious 8-Bit!

February 15, 2021 by 6 Comments

There was a time when visitors to London would carry an A to Z map to navigate the city’s Undergound railway system, referring to the iconic London Transport map printed on its back as they did so. Now it’s likely they’ll do the same with their smartphones, with apps ranging from simple analogues of the printed version through to fully annotated route planners with up to the minute train information. Is this a new technology, something only possible in the last decade? Serial British rail YouTuber [Geoff Marshall] thinks otherwise, and has programmed a Tube map on a vintage BBC Micro.

We don’t expect anyone to heft a pile of vintage hardware onto the Central Line at rush hour even though in reality he’s running it on an emulator due to his real BBC Micro being kaput. Perhaps someone should drop him a line about capacitor replacement in that power supply. But it does provide an entertaining jaunt back into afternoons in a 1980s school computer lab, with MOVE, DRAW, and PLOT commands as he wrestles with the limited colour palette of MODE 2.  The result only covers Tube Zone 1, or the very centre of London, so to visit London Hackspace you’ll have to remember to take the Bakerloo line northbound out to Zone 4 and disembark at Wembley Central.

Happily as you can see in the video below the break he enlists the help of a friend to run it on real hardware. He posted the code as a comment to the video but it’s really hard to find. Try this direct link and scroll down, it should be the first comment but you need to click “Read more” to unfold the code. We think the Tube Map would make a great test for any retrocomputer, so we look forward to this feat being repeated.

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A Lowly 8-Bit Micro Busts Copy Protection From The 16-Bit Era

July 16, 2020 by 6 Comments

When floppy disks were the data storage medium of choice, software companies and in particular game developers came up with ever more inventive ways to make them difficult to copy. Tinkering at the edges of the disc format standards didn’t come cheap though, and for example the Dungeon Master game for the Atari ST was reported as using $40,000 worth of custom hardware to achieve its so-called “fuzzy bit” technique. [Chris Evans] set out to recreate it, not by building a modern version of the custom hardware, but by doing it the hard way, with an early-1980s 8-bit BBC Micro home computer.

One could be forgiven for thinking that a computer sporting a 2 MHz 6502 would be unable to manage this task without extra hardware, and were it simply the 6502 itself you would of course be right. So to get anywhere he had to get creative with the Beeb’s built-in peripherals. Eschewing the floppy controller it was hooked up directly to the parallel port, and after a voltage problem courtesy of the drive’s termination resistors we’re taken through some of the 6522 VIA’s different modes in order to achieve a higher speed data burst than would normally be possible. All of these approaches hit the buffers though, until he looks at the 6845 video chip and uses its video output as a very fast shift register. With a custom cable and some work on special video modes, a home computer that would have cost several hundred dollars in the early 1980s can do the work of $40,000 custom hardware from later in the decade. Colour us impressed!

If you’d like to know more about the Dungeon Master copy protection, we’ve been there in the past.

BBC Micro header image: StuartBrady / Public domain.

How Did They Get Sampled Sounds From An SN76489 8-bit Sound Chip?

June 5, 2020 by 23 Comments

If you were lucky and had well-off parents in the early 1980s, your home computer had a sound chip on board and could make music. There were a variety of chips on the market that combined in some form the tone generators and noise sources of a synthesiser, but without the digital-to-analogue converters of later sound chips designed for sampled audio. They gave birth to chiptune music, but that was all they were made to do. The essence of a hack lies in making something perform in a way it was never intended to, and some game developers for the Acorn BBC Micro had its SN76489 producing sampled audio when it should never have been possible. How did they do it? It’s a topic [Chris Evans] has investigated thoroughly, and his write-up makes for a fascinating explanation.

So, how can a set of audio tone generators be turned into a sampled audio player, and how can it be done when the CPU is a relatively puny 6502? There’s no processor bandwidth for clever Fourier transform tricks, and 1980s tech isn’t set up for high data bandwidths. The answer lies in making best use of the controls the chip does offer, namely frequency and volume of a tone. A single cycle of a tone can be given a volume, and thus can be treated as a single sample of an unintended DAC. By using a tone frequency well above the audio range a suitable sample frequency can be found, and thus an audio stream can be played. The write-up has links to some examples in an emulator, and while they’re hardly hi-fi they’re better than you might expect for the hardware involved. Still, even at that they don’t approach this amazing 48kHz playback on a Commodore 64.

Header: SN76489, on a Colecovision console motherboard. Evan-Amos / Public domain.

Econet – Britain’s Early Educational Network

April 16, 2020 by 22 Comments

If you compare the early PC market for the US and the UK, you’ll notice one big difference. While many US schools had Apple computers, there were significant numbers of other computers in schools, as well. In the UK, pretty much every school that had a computer had an Acorn BBC Micro. [RetroBytes] takes us down memory lane, explaining how and why the schools went with Econet — an early network virtually unknown outside of the UK. You can see the video, which includes an interview with one of the Acorn engineers involved in Econet.

Nowadays, you don’t have to convince people of the value of a network, but back then it wasn’t a no brainer. The driver for most schools to adopt networking was to share a very expensive hard disk drive among computers. The network used RS-422, a common enough choice in Apple computers, spacecraft, and industrial control applications.

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Hackaday Links: April 5, 2020

April 5, 2020 by 8 Comments

Git is powerful, but with great power comes the ability to really bork things up. When you find yourself looking at an inscrutable error message after an ill-advised late-night commit, it can be a maximum pucker-factor moment, and keeping a clear enough head to fix the problem can be challenging. A little proactive social engineering may be in order, which is why Jonathan Bisson wrote git-undo, a simple shell script that displays the most common un-borking commands he’s likely to need. There are other ways to prompt yourself through Git emergencies, like Oh Shit, Git (or for the scatologically sensitive, Dangit Git), but git-undo has the advantage of working without an Internet connection.

Suddenly find yourself with a bunch of time on your hands and nothing to challenge your skills? Why not try to write a program in a single Tweet? The brainchild of Dominic Pajak, the BBC Micro Bot Twitter account accepts tweets and attempts to run them as BASIC programs on a BBC Microcomputer emulator, replying with the results of the program. It would seem that 280 characters would make it difficult to do anything interesting, but check out some of the results. Most are graphic displays, some animated, and with an unsurprising number of nods to 1980s pop culture. Some are truly impressive, though, like Conway’s Game of Life written by none other than Eben Upton.

The COVID-19 pandemic is causing all sorts of cultural shifts, but we didn’t expect to see much change in the culture of a community that’s been notoriously resistant to change for over a century: amateur radio. One of the most basic facts of life in the amateur radio world is that you need a license to participate, with governments regulating the process. But as a response to the pandemic, Spain has temporarily lifted licensing requirements for amateur radio operators. Normally, an unlicensed person is only allowed to operate on amateur bands under the direct supervision of a licensed amateur. The rules change allows unlicensed operators to use a station without supervision and is intended to give schoolchildren trapped at home an educational experience. In another change, some countries are allowing special callsign suffixes, like “STAYHOME,” to raise awareness during the pandemic. And the boom in interest in amateur radio since the pandemic started is remarkable; unfortunately, finding a way to take your test in a socially distant world is quite a trick. Our friend Josh Nass (KI6NAZ) has some thoughts about testing under these conditions that you might find interesting.

And finally, life goes on during all this societal disruption, and every new life deserves to be celebrated. And when Lauren Devinck made her appearance last month, her proud parents decided to send out unique birth announcement cards with a printed circuit board feature. The board is decorative, not functional, but adds a distinctive look to the card. The process of getting the boards printed was non-trivial; it turns out that free-form script won’t pass most design rule tests, and that panelizing them required making some compromises. We think the finished product is classy, but can’t help but think that a functional board would have really made a statement. Regardless, we welcome Lauren and congratulate her proud parents.

The BBC Computer Literacy Project From The 1980s Is Yours To Browse

June 30, 2018 by 12 Comments

In the early 1980s there was growing public awareness that the microcomputer revolution would have a significant effect on everybody’s lives, and there was a brief period in which anything remotely connected with a computer attracted an air of glamour and sophistication. Broadcasters wanted to get in on the act, and produced glowing documentaries on the new technology, enthusiastically crystal-ball-gazing as they did so.

In the UK, the public service BBC broadcaster produced a brace of series’ over the decade probing all corners of the subject as part of the same Computer Literacy Project that gave us Acorn’s BBC Micro, and we are lucky enough that they’ve put them all online so that we can watch them (again, in some cases, if a Hackaday scribe can get away with revealing her age).

You can see famous shows such as the moment when the presenters experienced a live on-air hack while demonstrating an early online service, but most of it is a fascinating contemporary look at the computers we now enthuse over as retro devices. Will the MSX sweep all before it, for example? (It didn’t).

They seem very dated now with their 8-bit micros (if not just for the word “micro”), synth music, and cheesy graphics. But what does come across is the air of optimism, this was the future, and it was packaged not as a threat, but as a good place to be. Take a look, but make sure you have plenty of time. You may spend a while in front of the screen.

We’ve mentioned int he past another spin-off from the Computer Literacy Project, the Domesday Project.

Thanks [Darren Grant] for the tip.