One of the major criticisms, often unfairly levelled against the humble old Acorn Electron, is its inability to communicate with the outside world - something the BBC Micro has never found hard to achieve.

Many people consider the BBC Micro to be a very easy computer to interface with other pieces of hardware by virtue of its many standard interfaces. Since the very earliest BBC Model B through to the latest Master 128, the interfaces have not been changed and even with Archimedes compatible ports will be available as add-on podules.

For the Acorn Electron it has already been the case that necessity is the mother of invention, and canny programmers have, on occasion, converted the Electron's only standard I/O port - the cassette interface - to act as an RS423 interface or any possible interface for many different applications.

Of course even the canny programmer is going to come up against a brick wall when it comes to implementing the Tube and the 1MHz bus on the Elk's standard connectors, and this is why Advanced Computer Products (ACP) have come up with a cracking new product called the Plus 5, a combined unit that plugs into the Acorn Plus 1 interface to give the humble old Elk a Tube interface, a 1MHz bus, a user port and three extra ROM sockets - all in one unit.

Advanced Computer Products have recently been given licence to produce the Acorn Plus 1 interface - the bridge across which *all* Acorn Electron interfaces are made possible. ACP's production of this board alleviates the chronic shortage of Plus 1 interfaces and should make expanding the Electron an easier task. Prior to ACP's licensing deal with Acorn, the only producers of Plus 1 type interfaces were Slogger with their ROMbox and ROMbox Plus interfaces.

The Plus 5 is a small board measuring 140mm x 110mm; it plugs into any of the two Plus 1 sockets with ease and is more or less a fully enclosed unit with two screws enabling access to the circuit board, so that sideways ROMs can be plugged into it. The current range of Sideways ROMs for the Electron is very poor although the compatibility ratio between Elk and BBC B is very good, especially for word processors and many of the Mode independent sideways ROMs such as the View series of ROMs.

There are three sockets supplied on the Plus 5, one of which is occupied by the Tube controller ROM which handles all of the Plus 5's I/O facilities and communications protocols required by the Tube, the 1MHz bus and the housekeeping tasks for the user port. The ROM is, to all intents and purposes, invisible to the user as there are no * commands to worry about, the aim being to have the Plus 5 devices operating *exactly* as they would on a BBC Micro or Master.

The Plus 5 unit is housed in a rugged metal case and will handle a lot of rough treatment. It is heavy enough to sit squarely enough in the Plus 1 socket and, if knocked, it will not fall out, as is the case with other less substantial Plus 1 cartridge devices.

For many people, this will be the Plus 5's raison d'etre as it allows complete compatibility between the BBC Micro second processors and the Electron, thus allowing large amounts of memory to be available to the user regardless of what screen Mode you are using. There is a marked speed increase in operation and the computer is more responsive as a result of connecting either a 6502 second processor, or a Master Turbo Board.

The Electron View package will happily work alongside the 6502 second processor, but because there are differences between the Electron and the BBC Micro's function keys, the BBC version of View (version 3.0 or Hi View if you have a Turbo board or a 6502 second processor) will not work, but the second processor's internal ULA is properly accessed by virtue of the fact that the BBC version of View's code is relocated to give 48,000 bytes free to the user in any screen Mode.

Electron View owners need not grumble; they are given nearly 30,000 bytes free to play with in any screen mode with all of the proper printer drivers accessible. Hi-Basic works properly, as does the rest of the View family, including Viewsheet, ViewStore and ViewSpell (surely the only spelling checker for the Electron?). The only piece of software that didn't work was 6502 second processor Elite, but this is due to the hardware limitations at the Electron's end!

As a side issue, I used a very early version of the 6502 second processor with an unnaturally long cable, which was my attempt at testing how critical the Plus 5 Tube timings were, which are as good, if not better than a modern Issue 7 BBC Model B, or a new Master series' Tube interface.

The Acorn Z80 system was even more impressive, although if you have a "foreign" DFS such as Solidisk's or the Cumana DFS boards then I suggest you replace it with ACP's very own 1770 DFS, as it is the only DFS I have yet come across that offers complete BBC 1770 DFS compatibility.

With the ACP 1770 DFS and a Plus 5, you can use most of the CP/M utilities. The 1770 DFS is needed to format discs, a task which requires a pretty close emulation of OSWORD &7F and sometimes falls foul of "foreign" BBC lookalike DFS systems.

All of the utilities and the bundled software work on the Z80 system; for Electron owners, this means that the complete suite of business packages can be used to great effect. As long time user of these packages, I was again pleased with the hardware's reliability and the system's ability to cope with large spreadsheets using the Accountant package and I even trusted it with my monthly accounts to the bank manager!

Although many users don't relish using CIS COBOL for their own applications, there is a growing user base for this old yet standard language, with many titles ready to run "off the shelf" as it were. Seeing CIS COBOL running on the Elk is a very strange sight indeed, and indeed represents the Electron's coming of age. Compile times for both CIS COBOL and UCSD-P FORTRAN programs (the latter isn't supplied with the Z80 software package) are just a little under that of the BBC Micro.

Graphplan is another package with its charms. Although attacked as an old and unfriendly package, I use Graphplan in preference to packages like InterChart which are, in my opinion, more unwieldy as a result of their user friendliness.

As the Electron is only being used for DFS activity, some buffering and the screen generating routines, there are none of the memory limitations associated with the Electron's greedier screen modes; as a result you can happily use Graphplan in Mode 1 to create effective and colourful displays from sources as widespread as CP/M spreadsheets to BBC database material.

The only package I would not touch with a bargepole on the Electron is the Memoplan package - for everyday use this is a real pig of a word processor of the "press a button and see how much text you've lost" variety, and I would honestly recommend the extra outlay in buying a version of Wordstar which is capable of much more (this review was written with Wordstar!).

The Acorn Z80 system on the Acorn Electron is as faithful as you can get. Only on rare occasions do the speed limitations of the Electron become apparent, and it is a very cheap way of getting CP/M machine from a computer costing as little as £50, especially when as little as three year ago, CP/M computers were costing up to £700.

Ahem... if I had said that the Acorn Electron was capable of emulating the IBM PC and running Flight Simulator, or even having a GEM front end, I think I would have been laughed out of the office. As it stands, the Master 512 board is the only second processor I was unable to properly test due to the fact that the 512 second processor couldn't be connected to the Tube socket at the time. However, since researching this review, Acorn have released their own Tube converter box for the Master 512 and the Turbo called the Universal Second Processor.

Looking at the hardware connections to the Master 512 from the Tube, I notice that very few changes have been made, none that are important anyway, so from a hardware point of view, the Master 512 should work on the Plus 5, which is great if you want to run MS-DOS, but a little bit of a problem for GEM and the mouse as the Electron addresses for the user port have been changed with reference to its reading and writing operations, a problem which can be overcome by changing the BIOS code accessing the User Port.

So, on paper, the Master 512 will work on the Plus 5 and the Tube, but using a mouse will prove nigh on impossible until someone comes up with different code to read from the Electron's User Port.

As soon as a Universal Second Processor box becomes available, I will relate my Plus 5/Master 512 findings through Feedback.

The 1MHz bus is commonly used by Acorn and third party hardware companies for memory expansions, hardware devices and second processors.

Unfortunately, the chances of running a second processor from the 1MHz bus are fairly small, unless the code is modified slightly as the 1MHz bus addresses have been moved; this means that some hardware interfaces will not work properly - although some will. Of the devices I tested few worked properly, I could not manage to get the Technomatic Z80 second processor to access the disc drives, and the Music 5000 package would hang up almost immediately. The Acorn Prestel Adapter and the Acorn Teletext Adapter are both non-starters as they only operate in Mode 7, but I was lucky with the Seaward Automatic Controls SACRAM 512K RAM module.

The general incompatibility is a bit of a shame really as devices like the Opus Challenger would go down a treat amongst Electron users who could do with an extra 512K as a RAM disc any time. The problem is that, instead of the complete page &FC (FRED) being available, only addresses of FRED &80-&8F, &A0-&AF and &F0-&FF are usable. The analogue input line is not available, but can be used as an output for the Electron's sound channel, if you wish to set the link on the PCB yourself.

Another problem is that the NNMI pin (Not Non Maskable Interrupt) is not a direct connection to the Elk's NNMI; instead, the input is regulated via the Plus 5's own clock which is placed on the trailing end of the PHI out signal. ACP's reason for doing this was to act as a buffer, stopping software from incorrectly reading the Electron's internal memory.

I hope to see ACP adjusted code for a number of products, an IEEE 488 interface would be interesting, enabling the Electron to be easily (and cheaply) incorporated into control devices especially lathe controllers and workshop and laboratory equipment - including HPIB plotters, laser printers and the like.

For the programmer, the 1MHz bus can be accessed either directly or indirectly, although it may be wise to stick to Acorn guidelines when accessing FRED, JIM or SHIELA, I don't see any reason to stick to these tedious methods as the chances are that the Plus 5 will become a standard interface for the Electron.

Like the 1MHz bus, the User Port has had to overcome some of the Electron's inherent differences between itself and the BBC Micro. The Plus 5 User Port is completely BBC compatible with the exception of the address of the 6522 VIA (Versatile Interface Adapter). Again, the Electron's memory map has caused this, to be relocated to FRED addresses &B0-&BF. While this causes no real problem to hardware devices being connected, changes to software are needed if the driving software is *looking* for the device.

So, devices such as trackerballs, mice and music keyboards can be connected to the User Port, although very few items of software for the BBC will work straight away, certainly MAX, Pagemaker and NovaCAD didn't, and PAL technology doesn't yet extend to the Electron, so the 3D graphics package from Silicon Visions doesn't work either, although all these packages show signs of running but without mouse control, all that is needed is for the software to be slightly modified so that it reads data from a different address relating to the Plus 5.

This is where ACP are one step ahead of us all here; they have released a modified version of AMX's Super Art package originally for the BBC B. A faithful conversion, Electron Super Art comes with the support ROM and is available as an extra to Plus 5 users and may attract customers to the Plus 5 just to run this package.

I am informed that Pagemaker, now titled Stop Press for legal reasons is being converted to the Plus 5 format, and I look forward to seeing it as Pagemaker is one of those programming feats that takes the BBC Micro a step above other popular computers.

Anyway, Super Art will happily work with the AMX mouse, the Quest mouse and the Wigmore mouse. My personal favourite is the Quest mouse, although AMX's model is very very nice and easy to use. The AMX software is well written as always, and it can quite happily run on your DFS-based disc system.

The use of a 1770 DFS is not critical here (unlike the Z80 package) as most of Super Art is written in a strange crossbreed of BASIC, Operating System calls (to the mouse support ROM) and machine code. This means that a Solidisk DFS can quite happily support the software as can a Cumana disc interface (with the replacement Slogger SEDFS ROM replacing Cumana's own DDFS-type filing system), although I honestly recommend anyone without a DFS to have a good look at the Advanced Computer Products 1770 DFS, as it has many advantages over other disc filing systems, both in features and by virtue of its compatibility with Acorn's 1770 DFS (in fact it holds the very same Acorn 1770 DFS ROM code).

The ACP Plus 5 is a truly innovative product, if only to allow connection to Acorn's ever growing family of second processor devices, although the implementation of a 1MHz bus and user port connectors must surely be considered fuel for the fire.

Running a 6502 second processor across the ACP Tube interface proved reliable and was certainly one of the easiest ways of gaining extra memory. The Plus 5 is also the only way of running a Z80 second processor on the Electron, and the option of running a Master 512 board is a tantalizing thought.

The 1MHz bus will need software support from ACP and other Electron peripheral manufacturers if it is to gain the compatibility it so richly deserves. If the Plus 5's 1MHz bus is not supported, then the 1MHz bus part of it will not get very far. I hope to see more BBC peripherals converted for the Plus 5 very soon.

The User Port is a very nice option, enabling the Electron to support many additional input devices including the AMX Mouse; again, like the 1MHz bus, this interface needs software support and a willingness on the part of BBC software houses to modify their code in order to make their packages run on the Plus 5. AMX's conversion job of the Super Art ROM if proof of just how effective this can be.

For many users, the prospect of running a second processor is enough, but with time, this product will form the basis of many a powerful Electron system. The AP5 costs £66.70 and is excellent value for money; the mouse and Super Art package costs £69.96 and includes the mouse, a tape containing the Super Art software (transferable to disc) and the mouse support ROM. You can buy both the Plus 5 and the mouse package for £125 which is certainly a good deal if you want to use your Elk as a drawing workstation.