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Amstrad CPC464 Home Computer

By a happy accident, Amstrad's first-ever home computer could become the MIDI micro of the future. David Ellis tells us why.


Music can't have been high on the list of design priorities for Amstrad's first entry into the home micro market, but could the 464's specification make it the budget MIDI computer of the future?


If you've never come across the name 'Amstrad' before, then the odds are you've had your head in the sand the past few years. No disrespect intended, but Amstrad's low-cost, racked audio systems do have a certain notoriety for being almost as commonplace as flying ducks making their way up the flocked wallpaper behind the imitation Chippendale sideboard. 'NQOCD' ('Not Quite Our Class, Dearie'), as one of my NHS colleagues put it. Fortunately, the CPC464 is a good bit more tasteful than all that and marks the latest and calculated marketing ploy of Alan Sugar, Amstrad's whizz-kid chairman: namely, a cheap well-turned out micro that borrows the best ideas from all around the micro field and comes packaged as a ready-to-run system.

Two options are offered to the consumer. First, the basic £229 version, comprising the micro with built-in cassette drive and monochrome monitor; and second, the deluxe £339 version, comprising all the foregoing but with a medium resolution colour monitor in place of the black & white one. And yes, those quoted prices are correct. When you consider that a colour monitor of the quality in the Amstrad package is likely to set you back the best part of £200, and a cassette deck around £30, it's not beyond the bounds of mathematical genius to see you're getting the actual CPC464 micro for just £100, give or take the odd green one.

Design



There's no doubt that the CPC464 is a micro that's designed to serve rather than be serviced. The chip count inside really is remarkably low - especially when viewed alongside the 100 or so ICs in the BBC Micro - and that can only mean a decreased chance of Sod's Law coming into effect. And although the direct soldering of the chips is something of a two-edged sword (the CPC464 is bound to be more difficult to service if one of the blighters does fail), the Amstrad's immunity to pounding fists dislodging chips from cheap sockets should make this a micro that's as suitable for the playroom as it is for on-stage MIDI sequencing. Furthermore, the low chip count, judicious use of air vents and separate power supply can only mean that the 464 will also prove less prone to the over-heating problems that have always thwarted the attempts of owners of BBCs and Apples to get their charges performing properly on the stage of the Hammersmith Odeon and other emporia of audiovisual delights.


The Amstrad has a full QWERTY keyboard, a cluster of cursor keys, and a numeric keypad that doubles as a group of function keys. Alongside, there's the data recorder (with a mechanism borrowed from Amstrad's hi-fi ventures), but whilst it's obviously good for the first-time user to have a built-in cassette machine, it's also true that the addition of this extends the length of the CPC464 to a somewhat unwieldy number of inches. I must admit that if I'd been designing this computer, I'd have considered some sort of modular construction (like that employed by some mixers, in fact) that allows either a data recorder or disk drive to be slotted on the end of the main unit. As it is, adding a disk drive to the system entails finding yet more space on an already crowded desk or table.

At the back of all this, there's a row of connectors for making the necessary micro moves to the outside world. The Amstrad's is a plentiful array, but one connection that is lacking is a duplicate of the cassette I/O, a fact that might seem a bit thick if you've already got a favourite cassette machine (unlikely, I admit) that you want to use with the CPC464 or if the built-in unit goes down on you.

Mind you, the Amstrad has almost everything else. First, there's the inevitable (on a machine that's destined for the games market, anyway) joystick port. Next, we find a Centronics-type printer connector: unfortunately, this is of the edge connector type rather than a decent D-type socket, which doesn't augur well for secure connections. After that, we come to the expansion socket - again, an edge connector - which is actually labelled 'floppy disk'. Now, assuming that most 464 purchasers will eventually realise the sense in going 'floppy', one wonders how Amstrad intend making provision for other peripherals to be added on once the disk drive is in place. I suppose it's the old stacked connector syndrome again, but to my mind, it seems short-sighted not having separate connectors on the back for the disk drive and general system expansion. Oh, well, I suppose I shouldn't grumble too much at this price, but it does strike me that some corners aren't worth cutting.

However, the disk drive that Amstrad intend supplying later on this year should actually give you much more than yer average floppy. Not only does the £199 price tag get you a 3" Hitachi-type drive (the sort that withstands idiotic advertising executives indulging their fantasies by driving over disks with 10-ton trucks) with interface, but also extra memory, the CP/M operating system, and Digital Research's LOGO to boot. A complete CP/M system for well under £500, in fact. Pretty impressive.

The remaining trio of back panel connectors concern sound, video, and power. Even though the CPC464's sound source is the bog standard General Instruments AY-3-8910, Amstrad's designers have made sensible use of the three separate channel outputs by providing stereo positioning of same. And although the basic machine has a really grotty speaker doing its best to distort like mad, one of these connectors allows the stereo sound to be piped off to your hi-fi, Amstrad or otherwise.

The CPC464 also breaks with tradition in the way it organises its power supply. In contrast to most machines that either put the power supply in an ugly, chunky box outside the micro or cram the necessaries under the keyboard, the 464 puts the power supply in the monitor, with an umbilical power cord supplying the main unit with the necessary juice. Finally, and next to this, there's the video output itself.


Performance



Seeing that one of the perpetual preoccupations of the human condition is to know who or what is bigger and better, computer magazines routinely use so-called 'benchmarks' - short programs which illustrate one or another aspects of a machine's performance - to judge a newcomer against the competition. Doing this with the CPC464 gives the following results against the BBC Micro, Apple II, and Spectrum for three benchmark tests:

Test 1 Test 2 Test 3
BBC Micro 102 sec 3 sec 12 sec (Mode 7)
Amstrad CPC464 156 sec 3 sec 40 sec (Mode 1)
Apple II 257 sec 4 sec 18 sec
Spectrum 48K 540 sec 8 sec 55 sec

Test 1 is a string sort program that takes the numbers from 1 to 100 inclusive and sorts them so that they're in reverse order, Test 2 merely instructs the micros to add up the numbers between 1 and 1000 and then print the result, while Test 3 does the same except that each number has to be printed on the screen in turn, thereby giving some idea of how good the machines are at handling text display.

In fact, the display features of the CPC464 are really quite impressive - a maximum number of 16 colours (from 27) with a maximum resolution of 640x200. That compares with 8 of 8 at 640x256 on the BBC Micro. Three different graphics modes are available and, unlike the BBC, the more memory-greedy modes don't chew up the memory available to the user, meaning that 42K of the machine's 64K is always available for use. The one drawback to the generally very acceptable colour monitor supplied with the review system is that the mode supporting 80-column text (essential for serious word processing, I'd say) just wasn't clear enough for extended use. That means having to use the higher resolution monochrome monitor instead.

But hold on, what happens if you want to use the CPC464 for both word processing (where you want clarity) and games (where you want colour)? Well, therein lies the real dilemma posed by Amstrad's over-enthusiastic packaging. If you buy the version with colour monitor and then decided to add on a black and white one of non-Amstrad pedigree for the purposes of word processing, you'll find that the colour monitor still has to sit where it sat before for the simple reason that (a) the micro gets its power supply from the monitor, and (b) the power cable is too short to allow the monitor to be shifted to one side. And of course, exactly the same problem would apply if you'd bought the monochrome version first and subsequently wanted to use the CPC464 with a colour monitor. Amstrad's way around this problem is to sell a separate modulator/power supply for £30, but you still have to buy the monitor in the first place, which means that you're paying for two power supplies. Clearly, not a very satisfactory state of affairs.

Locomotion



For most users, the Amstrad's performance will be judged on what they can get out of the resident version of BASIC - the so-called 'Locomotive BASIC.' In fact, this is quite a nice BASIC, even if it does lack the multi-line procedures or functions with the facility to pass local variables that makes BBC BASIC such a strong contender in the structured programming stakes. Unlike BBC BASIC, there's no 'REPEAT... UNTIL' loop structure, but it does have 'WHILE... WEND' instead and, aside from the fact that I love the archaism of wending one's way in a program, the Locomotive way of doing it means that the test for executing the loop is performed at the start rather than the end of the process, which is intuitively neater and more efficient.

Also very neat is the feature of Locomotive BASIC that allows it to handle Z80 interrupts directly. Typically, this means you can have a number of programs running alongside each other with each grabbing the processor's attention from the other according to where they're at. Lots of musical applications in that. In addition, Locomotive BASIC also has a special ON SQ GOSUB command which checks whether there's space in a given channel's sound queue and interrupts to a sound subroutine automatically: very similar to the queuing side of sound on the BBC Micro, really.

Actually, there are quite strong similarities with the BBC Micro on a more basic side of the CPC464's musical capabilities. For instance, both have a multi-parameter statement called SOUND which orders all the necessary values together before they're sent off to the operating system's sound queues and the sound chip's registers. But one black mark Amstrad do get is for the way in which pitch values are programmed. The Beeb makes the sensible move of having a linear series of values going from 0 to 255, with 0 being the B an octave below middle C and 255 being God knows where very high up. So, wherever you are in the range, an increment of 48 changes the pitch by an octave, 20 by a fourth, and so on. All very sensible. Amstrad, on the other hand, have insisted on perpetuating the tiresome and entirely unmusical tradition of plugging in very large values that have no correlation with musical intervals. So, a 'period' of 3822 gives a bottom C, 1911 the C above that, and 956 the next C up. In other words, you're obliged to work out pitchings on an inverse logarithmic basis. Awkward in the extreme, if you ask me.

On the other hand, Locomotive BASIC does separate out the BBC's ENVELOPE statement into a more manageable format, with one statement governing the amplitude envelope and the other the tone envelope (sic), ie. 'ENV' and 'ENT'. So, if you want to use one without the other, life is marginally easier. For a taste of similarities and differences, Figures 1 and 2 give a couple of examples of sound programs on the BBC Micro and the CPC464. Program 1 is designed to maximise the gruesome side of micro music, by (mis)use of the RND function, simulated reverb (the two silent SOUND statements - lines 50 & 60 on the BBC, 60 & 70 on the Amstrad), and pitch offsets. Program 2, on the other hand, is designed to appeal to the more romantic side of the spirit and, unlike records, it won't get stuck at the wrong moment... (No prizes for guessing the source of the two bars of rhythm held in the DATA statements.)

Figure 1: Fangs for the memory/filename: CREEPY/Acornsoft (C) 1984
Figure 2: Music for '10'/filename: DUD/Acornsoft (C) 19B4


Conclusions



Well, to be candid, I think this is a very nice micro. On the design side, there really are very few miscalculations, so it's a shame that the same isn't also true about certain aspects of interfacing, pitch values, and power supplies. But these are small points, and I'm sure the CPC464 will sell and sell.

From a musical viewpoint, there's no point in beating about the bush when it comes to the less than ingratiating capabilities of the Amstrad's AY-3-8910 sound chip. So, let's remind ourselves instead of the requirements for a micro to be used in MIDI applications - reasonably fast, plenty of memory, good graphics, a full-size keyboard, easy interfacing, decent storage capabilities, and a fair price. The CPC464 has them all. So come on, all you MIDI software companies, forget the Spectrum - this is the MIDI micro for 1985!

RRPs are included in the text. Further information from Amstrad, (Contact Details).



Previous Article in this issue

The Programmable Digital Sound Generator

Next article in this issue

BeeBMIDI


Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.

 

Electronics & Music Maker - Nov 1984

Computer Musician

Gear in this article:

Computer > Amstrad > CPC464

Review by David Ellis

Previous article in this issue:

> The Programmable Digital Sou...

Next article in this issue:

> BeeBMIDI


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