Revitalizing a BBC Micro

BBC attached to Amstrad monitor and giant twin floppy drives Moving house means making possessions count, so my collection of vintage computers has shrunk over the years, and the bar keeps getting higher. Right now:

  1. It works – Test it, repair it or part with it. A wealth of online technical information makes this easier than ever.
  2. A small footprint – Eject unusable peripherals and accessories. Keep the essentials.
  3. Make it usable – Forget slow-loading tapes and corrupt disks. Fast loading is essential.
  4. Something special – It should be a collectable or one I have a connection to.

Recent casualties were my Apple ][e (no disks), Acorn ARM (wouldn’t boot) and Commodore VIC 20 (poor state). Next up is my Acorn BBC Micro B:

Physical inspection

My ‘Beeb’ is in good condition and works well, but the case screws have long since disappeared (a common theme in my collection), and it needed a good clean. These older mechanical keyboards attract dust and dirt.

Schools were filled with BBCs in the 80s and I’ve written about the origins of this love affair before. I learned first BBC BASIC and then some 6502 assembly (mixing it with Basic) while at school. I later picked this machine up around 91 after seeing a local paper advertisement.

A giant twin 5.25″ drive housing system (shown above) contained my one still-functional floppy drive. I want to read physical disks but keep the minimal footprint so, I transplanted the floppy drive into a 5.25″ externally powered CD-ROM enclosure. Big reduction.

The BBC Micro has a few video output options – UHF, composite over BNC and RGB over 6-pin DIN connector. By a staggering coincidence, the pin-out is identical to the Amstrad CPC. This means it works directly with my Amstrad monitor and no adapter cable is required this time!

Replacement media, SD cards via GoSDC

BBC Micro with SD Card fitted

SD cards are my replacement storage of choice for vintage systems. I chose John Kortink’s GoSDC for the following reasons:

  1. Supports MMC, SD, SDHC up to 32GB
  2. Internally fits into a spare ROM socket
  3. Adds operating system commands for great integration
  4. Supports disc images, tape images and ROM images

Retro Isle comprehensively reviewed GoSDC in February (2015) and have a bunch of usage tips and tricks too.

Getting started with GoSDC

GoSDC installed inside a BBC Micro model BThe device plugs into a ROM slot but to make life easy, you can give it access to a second one so it can patch the filing system. The docs are complex as they describe the many possibilities available. Here’s my setup that works well on a BBC Micro Model B (known as Option B in the docs):

  1. Remove Acorn DFS ROM
  2. Fit GoSDC in slot third from right
  3. Fit cable from GoSDC jumper (middle-left) to pin 6 up from bottom right
  4. You should be left with the Acorn OS ROMs in the ROM sockets to the left of GoSDC

Once fitted, slide in an SD card and power up your BBC, and you should see the usual welcome screen. Then type *SDCINFO and see the results:


BBC Computer 32K

Acorn DFS

BASIC

>*SDCINFO

GoSDC (mbe) 1.05 (01 Sep 2014)

ROM slots : main 15, free 13

Flash ROM : S25FL007, 1024 KiB

Flash card : SDHC, 7580 MiB

Available areas
---------------
X :     416256 bytes
1 : 4294966784 bytes
2 : 3653238784 bytes

>

If you see ROM slots main and free with numbers your device is controlling two slots correctly and can patch the DFS for you. If not, check the adapter and cable.

If you see “GoSDC : No flash card inserted” check the card is securely in and power cycle the machine. If it still doesn’t recognize the card try another. Note: When switching card you will need to press CtrlBreak for the machine to recognize it.

The first time you use a card, you’ll need to format it. The command and subsequent output should look like this:

>*SDCTOOL SDCFO
Formatting area ... done
Verifying format ... ok
Please hard-reset your machine now
>

A card greater than 4GB will use 4GB areas created that are switchable with *SDCAREA number. I’d recommend switching to the additional areas, formatting and CtrlBreak after each before you put any software on it as this command wipes it out again.

Finally, you’ll need to tell GoSDC to provide a patched filing system like this:

*SDCCONFIG FSNR 1
*SDCCONFIG FSRM 13
*SDCRESET
  • 1 sets Acorn DFS on my machine, although the docs say it should be 2
  • 13 should match the free ROM slot shown in *SDCINFO

If you mess up your ROM selection and are unable to type because of ‘No drive’ do not fear! Press caps-lock and break twice to get the prompt back and choose another.

Finding old software

One option is to image all your floppy discs to SDcard, but you may find those discs are corrupt. Thirty-year-old floppy disks are not reliable.

Another option is to download software online. This redistribution is a grey area when the software is copyrighted but no longer sold. Many authors allow it (e.g. Ian Bell and David Braben of Elite fame). A comprehensive site to check out is Stairway to Hell, which honours copyright holders requests.

The author of GoSDC supplies Windows scripts to download, unpack and write the files to disc which I took the liberty of porting to Bash so they could be used on Mac OS X and Linux.

Purely based on subjective childhood experiences…

  • Elite a 3D space trading game so good they recently Kickstarted Elite 4
  • Citadel one hundred screens of arcade adventure madness
  • Chuckie Egg quick platform dash with birds, ducks, eggs and platforms
  • Repton Boulderdash to the next level, try 1 or 3, Repton 2 is insanely hard
  • Granny’s Garden educational fun alas distribution is denied as they sell an iPad version

Using GoSDC

Once the card is loaded with software, the actual commands are simple:

*SDCLIST

Will list the contents. You’ll likely want to put a wildcard after it to limit the results. Remember CtrlShift pauses the screen on the BBC!

Then, to mount a disc, you use *SDCDISC and provide the name to mount. You can also use wildcards here, and it picks up the first match. e.g.

*SDCDISC *Chuckie*

Once mounted hold down Shift and tap Break to boot the game (or educational title, right?)

A few other useful commands are:

*. List contents of a disc
*EXEC !BOOT What ShiftBreak actually does
CHAIN "filename" To LOAD and RUN a BASIC program from disc
*filename To execute machine code programs from disc

I put some BBC Micro tips and tricks together, or you can grab PDFs of pretty much every book created for the BBC Micro.

You can also see which discs are currently selected using *SDCDISC with no arguments. You’ll note you can mount a second disc, and the command to do that is *SDCEXTRA with usage otherwise exactly like *SDCDISC.

GoSDC can do much more, including imaging your real floppy discs and writing them back out. Be sure to check out the comprehensive documentation, which includes how to upgrade the firmware (use another memory card as that process uses FAT no the GoSDC file system)

Out for Pi Day!

Pi Day (3/14/15 = 3.1415) was last weekend, and my work put on a session for kids about how to program the Raspberry Pi using Scratch and a breadboard (using CanaKits so we had a breadboard, LEDs, switches, wires, resistors, and such).

The original goal of the Raspberry Pi was inspired by the BBC Micro. The name “Model B” is a nod to the original! Few people seem to realize that the manufacturer of the BBC Micro – Acorn – went on to create a processor for its follow-up machine the Acorn RISC Machine - or ARM for short. That’s right, the Pi is powered by an Acorn processor design (like most smartphones) so, it made sense to bring it in.

It was a hectic event with little time to show the machine. While sitting there, it popped a capacitor in a puff of smoke!

Power supply repair

Despite the noise and smoke the dying capacitor didn’t stop the machine from working. These troublesome electromagnetic interference suppression capacitors are not involved in the power circuitry. Still, it should be repaired, and I may as well replace the other X2 film capacitor as they have expired over the last 30 years.

BBC power supply with blown X2 capacitor BBC power supply with new X2 capacitors

I picked up a couple of RIFA PME 271 M capacitors – 100nf and 10nf – (with a matching pitch so they would fit correctly) from Mouser for less than $2 each plus shipping. Five minutes of de-soldering and soldering later, and it was good as new!

[)amien

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