Difference between revisions of "472"

Revision as of 17:09, 11 April 2010

Spanish Amstrad CPC 472

The reason Amstrad released a special version for the spanish market was a law (RD 1250/1985) that said that every computer with up to 64kb should adhere to some rules - namely, have extra keys for the spanish language, and the video hardware had to be able to display spanish characters; otherwise an extra tax would be levied. So Amstrad soldered in an extra 8KB which was not, however, usable by the machine since it was not connected to anything else.

Left side of the CPC472 motherboard, revealing the location for the presumely 8KB expansion memory.

The 8KB extra memory, was a 4164 DRAM chip (64Kx1bit). The DRAMs 1bit databus didn't suit too well to the Z80s 8bit bus, moreover, the daughterboard didn't receive /RAS and /CAS signals which are usually required for DRAM addressing & DRAM refresh. So, even if it would have been functional, the RAM could have been only accessed via complicated software mechanisms; like loading the address LSBs into IR register, and then INning from address MSBs.

Because there was no space for a new chip, Amstrad designers took off one of the ROM chips, and put it in a daughter board, along with the 4164 chip. Wires connected pins at the ROM from the daughter board to the corresponding pins on the main board. The wires were hard enough to make difficult to turn the daughter board over and reveal the trick: no wires were connected from the DRAM chip to the main board. Even the supply pins were not connected!!

While based on the CPC 464, at least some of the 472s got the ROM v2 with Locomotive BASIC 1.1, which normally was built into the CPC 664.

After the rule changed there was also a CPC 472 with spanish keys and BASIC 1.0 available for a very short time.

Motherboard close-up, showing the "8KB" extra memory, next to the 40037 ROM chip.

In some interviews, Amstrad developers stated that they have never heard of the CPC472, so it's possible that the daughterboard was made by Indescomp (the spanish distributor), not by Amstrad.

Timeline

1. CPC464 with British Keyboard

Before the law was invented (in 1985), the normal CPC464 may have been sold in spain.

2. CPC472 with British Keyboard

Faked 72K RAM to bypass the law. These units included a CPC664 ROM (not CPC474 ROM), thus supporting BASIC 1.1 - the spanish manual claimed that the extra 8K would be required for BASIC 1.1 - this was total nonsense, but it "explained" why users didn't have access to the extra memory.

3. CPC472 with Spanish Keyboard

After the law was changed (now including also computers with more than 64K), the remaining CPC472 units were fitted with spanish keyboard, and spanish CPC464 ROM. But still including the 72K daughterboard.

4. CPC464 with Spanish Keyboard

Once when the remaining CPC472 units were disposed, the fake 72K project was discontinued, and the CPC464 was re-invented. But now having spanish ROM and spanish keyboard.

The Daughterboard

The picture of the desoldered PCB shows the fake connections: Only the ROM (IC103) connects to the ribbon cable. The wires going to IC126,IC127,IC128 do end shortly before actually reaching the soldering points; this is hidden underneath of the white paint layer - but still visble when having a closer look. There are even a few perfectly visible interruptions that aren't covered by paint (seen near IC126).

• Daughterboard
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  Top, mounted

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  Bottom, mounted

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  Top, desoldered

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  Bottom, desoldered

More Pictures

• CPC472
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