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Meet the Relatives

Kevin Thacker investigates the CPC's mysterious East German cousin, the KC Compact

The KC Compact is a clone of the Amstrad CPC. It was made in 1989 by VEB Electronik to celebrate 40 years of the German Democractic Republic. Soon after the Berlin Wall was taken down, east merged with west, and Germany as we know it today was born. However, production of the KC Compact ceased.

The computer is rare, and can fetch a high price on Ebay or other auction websites. I've seen them go for as much as �200. Initially I was part of a bidding war and lost, but then I was lucky, and found a person willing to sell his KC Compact. He accepted my more reasonable offer, and I imported it into the UK.

Since then I have discovered more about it, and I will tell you what I have found to date.

From the outside

Visually, the KC Compact is a cuboid shape (technical speak for a rectangular slab). The unit stands approx 2.5cm, similar to a CPC6128, is not as wide, but approx 50% bigger in depth.

The case is the same design as the BIC A5105, a educational computer also made by VEB with the same colour as the CPC6128+. The keys are flat and not as tall as the CPC keys, but have a better feel. The arrangement, of course, is different and the F5-F9 keys are missing. The Return key is below the cursors, and takes some time to get used to.

The connectors are also different. Looking at the back, from left to right come: Power-DC (a 'Telefunktion' connector), Tape (a 5-pin DIN socket, same as the CPC), UHF (a aerial lead which plugs into a TV), TV-RGB (a SCART socket), Printer (a 25-way D-type connector, same as the CPC+) and Expansion (a 50-way PCB connector).

On the right, from left to right there is: a power switch, JOYST (a 9-pin d-type; same as CPC joystick) and SOUND (a 5-pin DIN which can be connected to some old-style stereos/amplifiers).

The aerial and SCART work well with modern TVs, which can handle the different PAL signal encoding used by German TVs. If you're unlucky you won't get a stable picture on an older British PAL TV, or there will not be any colour. (However, I have been successful connecting the KC Compact to a CPC+ monitor.)

I tried two modern TVs, a 14-inch Sony portable and a large 22-inch Panasonic. The picture on the portable was visible but blurred � the TV definitely had a problem with the signal. I tried connecting the SCART, and for a few seconds, the picture was perfect. Then it shifted and it was difficult to see what I was typing. In contrast, the Panasonic didn't have a problem. The picture was perfect using the aerial and SCART socket.

The cassette socket on the KC Compact is identical to the CPC's, and I used my old cassette lead with great success. I've not tried the other connectors yet, because I need to make some conversion leads.

The KC Compact requires a seperate power supply block to convert mains voltage (approx 230V AC at 50Hz) into the strange -20V DC and 20V DC required by the computer. Internally the computer has a voltage regulator which converts this signal into -12V, +12V, -5V and 5V. These voltages are also available at the expansion connector. (I'll have to be careful when I make my conversion lead, because I don't really want to fry any of my CPC peripherals!)

From the inside

So much for the external differences. Let's move onto the software and hardware differences.

When the computer is switched on, the famous yellow on blue screen appears � but with the following, rather different, text.

And yes, it is the same Locomotive BASIC v1.1 as used in the CPC6128. So CPC BASIC programs will work without any changes.

In fact, the operating system is also from a CPC6128, but with some extra patches added:

1. the start-up message has been changed;
2. there is extra setup code to initialise the hardware of the KC Compact; and
3. there is a simple communications interface built in.

Although the computer has the ROMs from a CPC6128, it only has 64K of RAM.

The simple communications interface allows a 256-byte sized program to be downloaded into the KC Compact memory. A lead attached to the expansion connector is then hooked up to another computer, so the two machines can communicate. I guess that this feature was used to test the computer during development, but I can think of other uses too � for example, it could be used for 'cross-development'. (This is a method to develop a program on one computer and test it on another. The program is sent from the development machine through a cable to the destination machine, and run there. Because you don't have to keep swapping between source code and the resulting program on the same machine, this makes program development much quicker.)

The extra setup code initialises the Zilog Z8536 counter and timer IC. This IC is used to generate the interrupts, and is also connected to the printer connector. In the CPC design, the interrupts are generated by the Amstrad-designed Gate Array: the KC Compact doesn't have a Gate Array, and the functions of this chip are emulated using lots of TTL logic chips. (The ICs inside the computer are mostly Russian knock-offs of familiar chips. For instance, the U880 is the Russian equivalent of the Z80 CPU.)

Compatibility

The cassette is entirely compatible with the Amstrad, and normal CPC programs can be loaded using it. However, there may be problems running some games. If a game relies on the exact interrupt generation mechanism of the CPC, then these are likely to fail. I haven't tested any demos yet, but I expect there will be serious problems! (Demos often don't work on different models of the CPC, because of the different 6845 CRTC ICs used. But the KC Compact has different interrupt generation and possibly different instruction timings, so could cause more problems.)

However, I still believe that the KC Compact is 95% compatible with the CPC. In some respects, it is actually more powerful:

1. The interrupts can be re-programmed. They could be set up to trigger every screen line; trigger once; or at any rate. This would allow interrupt-driven sample sound to be played very easily, something which requires painstaking CPU instruction timing on the CPC.
2. Also, since the Z8536 is connected to the printer port and is a I/O chip, we can use this as a general purpose 8-bit input/output port. This is far superior to the write-only 7-bit printer port of a standard CPC! This port could be used to transfer data between machines more quickly, to control another device, or for many other purposes.
3. Since there is a internal power regulator generating 12V and 5V, it is possible to connect external devices without needing additional power supplies.
4. From the schematics, I can see that the Z8536 is also connected to other parts of the KC Compact. I haven't found out yet whether it can be used to reprogram the video hardware, or to speed up the computer by reducing wait states.
5. The video hardware uses a ROM for the colour-palette lookup. This allows 4 different levels of red, green and blue. Therefore it might be possible to have a palette of 64 colours.

Some of these possibilities are speculation, based on observations of the schematics, and will only be proven when I have the time to try them out.

Clone king

VEB's cloning project didn't stop with the CPC hardware. They also cloned some software and peripherals.

Fifteen games packs were released (SpeileBox 1-15). Some contained software written by VEB, usually in BASIC; others contained patched games. These include modified versions of Speed King by Mastertronic and Arkanoid by Imagine/Ocean.

VEB also released some utilities, including a assembler/monitor program called ASMMON, which was actually Hisoft's Devpac! The amount of KC Compact-specific software is limited: I suspect most of it doesn't use the Z8536, so it should also run on a standard CPC.

VEB also made their own disc interface. The interface contained the same disc controller as the CPC, but also their own 64k memory expansion, which is nearly compatible with the CPC 6128's extra memory and dk'Tronics' RAM expansions. This interface was connected to a 5.25" disc drive. The disc operating system, again, was a patched version of AMSDOS, called BASDOS.

However, when it came to CP/M, VEB chose instead to use MicroDOS, a clone which also ran on their existing KC85/3 and KC85/4 computers. (These computers were not compatible with the CPC.)

Investigations are continuing

This is what I have found to date from various sources. I'm continuing to gather information about the KC Compact: if you have Internet access, you can read the latest information on the Unofficial Amstrad WWW Resource, http://andercheran.aiind.upv.es/~amstrad/.

Do you know any more? If so, please contact me. All contributions are welcome, and you will be credited.

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