rob.rho.org.uk

In a recent post, I alluded to my “newly tricked-out Electron”, and promised more detail in a future post. This is that post, and pictured above is the Electron in question, with its new friend the Plus 1 Mini.

While of course dear to my heart, the Acorn Electron was never what you’d call a powerhouse. Its 32K of RAM wasn’t terrible on paper, but the lack of a true text mode meant that much of it was given over to the screen. Moreover, the base unit had limited connectivity, only video (RF, composite and RGB) and a cassette interface for mass storage. What there was was an expansion slot on the back of the machine that gave access to almost all of the internals, and this offered a way forward.

Due to the Electron’s limited success in the market, and the more general problems they were facing, Acorn only released two expansions (the multi-purpose Plus 1 — more on that below — and the Plus 3 disc drive). However, third parties such as Slogger and Cumana picked up the mantle, producing a wider range of peripherals and keeping the ecosystem going for a few years longer than it might have.

More recently, the retro community (such as the fine people on StarDot) have continued this tradition, and there are numerous more modern options that open up interesting possibilities. I’d been eyeing up various of these for a while, but was inspired to take the plunge by this post from Mark Moxon (who’s work on Elite is well worth checking out if you haven’t already).

The Plus 1 Mini, unlike some other options, doesn’t exactly ape the physical form of the Acorn Plus 1 — as you can see in the photo, it’s not quite as wide as the Electron itself — but is similar in spirit in that it offers a grab-bag of useful capabilities in a single package. There are the obvious and characteristic dual cartridge slots, and a joystick port (Atari-style, rather than analogue). Inside are headers to connect a Raspberry Pi Zero to emulate the Tube second processor interface, which is definitely something I want to try out in the future. However, there are two items in particular that make a night-and-day difference to the capability of the machine: 128K of sideways RAM, and an SD card slot.

What makes the RAM sideways is a whole topic in itself, but suffice to say that it’s not just more of the same. The 16-bit address bus means the 6502 can only reference a 64K address space, which needs to cover both RAM and ROM, including the OS. To make use of more than 64K, a fair amount of bank switching is required. Fortunately, Acorn MOS provides a well developed system for doing this. An added bonus is that the sideways RAM isn’t subject to the compromises the Electron makes to share the main RAM with video, and so access is twice as fast.

The biggest benefit, though, is the SD card slot, which essentially emulates a stack of floppy disks¹. Previously I’d been using the excellent PlayUEF to load cassette images, which allows you to pick from a vast library of software and load it with a great facsimile of my 1980s experience. However, I never figured out a good way to get the reverse process working, and thus never had a way to save work from the Electron. This severely limits the kind of experimentation you can do with the machine.

With the Plus 1 Mini, I can not only try out an even wider range of software (including ROM images, which can be loaded into sideways RAM), but can actually do things that last across multiple sessions. I’m excited to see what possibilities this opens up. I’ve already found that the expanded Electron is a significantly more capable (even useful) machine, and it seems clear that it could indeed have been the basis for a thriving ecosystem if history had gone a little differently.