Interface extras for Kenn Garroch's Electron

The Plus 1 closes the gap between the Electron and the BBC, since it gives the former all the interfaces many machines have as standard such as a Centronics, analogue joysticks, and cartridge software.

The Plus 1 has the Electron's creamy colour, fits on the back and bolts on in much the same way as the Spectrum's Interface 1. It is the same width and height as the Electron and extends back about 3".

Just remove the expansion bus cover and slot it on, do up the bolts and it's ready to go. After switching the machine on and typing *HELP the Electron comes up with:

EXPANSION 1.00
ADC/PRINTER/RS423

RS423? I could not find any other hole mark or scratch resembling an RS423 port. Acorn's explanation is that an RS423 will be released along with a few 'other' expansions on cartridge, hence the need for internal software to run it.

On top of the Plus 1 are two slots for the cartridges. These have flip-down lids and are about half as long again as the cartridges. The rear of the Plus 1 contains the other two interfaces, the Centronics port and the analogue joysticks port. The latter does not appear to support the light pen facilities that the BBC's does.

The Acorn spiral-bound manual covers everything relating to the interfaces, as well as a number of the 'new' *FX commands necessary to run the various devices in the Plus 1.

The manual covers everything from installing the Plus 1 to what the new and altered *FX commands do.

There are also complete instructions that should allow the printer cable to be wired up.

Connection to the analogue port is via a 15-pin 'D' plug. This is the same as that used for the BBC joysticks so they are completely compatible. Attaching other analogue inputs to the port it also possible if they fit the specifications.

The ROM cartridges come in two forms: the first loads itself into memory much the same way as the cassette and disk systems. The second has the same effect as the sideways ROMs on the BBC, i.e. they are switched into memory instead of the Basic (between &8000 and &C000). The *ROM command switches in the cartridge filing system and it is possible to use, from the current language, *EXEC, *CAT, *LOAD, etc.

The Plus 1 is as simple to use as it is to set up. The analogue port will probably be mainly used for joysticks. These work using the ADVAL command - the manual says ADVAL 0 to 4 should be used to read the joystick.

Using the arguments 1 to 4 returns A/D values between 0 and 65535 in steps of 256, for each of the inputs. In fact, it is possible to get the readers between 0 and 255 in steps of 1 by using the arguments 5 to 8 respectively.

To use the printer, simply plug it in, hit CTRL-B or VDU 2, and away it goes. It may be necessary to enter *FX 6 to make the Electron send line feeds, but that depends on the printer.

Loading the software from the ROMs takes some time, as long as a disk load on the BBC. To use the software, insert the cartridge and turn the power on. The front slot then auto-boots with the normal Acornsoft loading screen. To load the program from Basic the *EXEC !BOOT command can be used, but again, this only loads the front cartridge. It is possible to load any of the programs with LOAD or *LOAD and a catalogue of both cartridges is available with *CAT or *.

The Plus 1 complements the Electron, though one can't help but think the analogue and printer ports should have been fitted as standard.

The cartridge software is more convenient and reliable than cassettes but slow, considering the load is a direct memory transfer.

It seems the Electron will never be brought up to the BBC's capabilities since there are no plans to produce a Tube interface from Acorn. But the Plus 1 goes part of the way and does it well.

Some new *FX system commands available with the Plus 1:

The following is available from an OSBYTE call only: A=128, X=0 to 4, X=0 returns the number of the last analogue channel sampled, in Y.

X=1 to 4 returns the last reading of the channel specified in X as a 16-bit integer in X and Y (low and high).