Harlequin Questions

[8008guy]

Hi all,

I'm looking at buying and building a Harlequin. Can anyone relate their experiances? How compatable are they to a real spectrum? What keyboard are available to use.

Any other comments are helpful.

Len

[1024MAK]

Hi Len

Compatibility is high, but there are a couple of very slight differences. These do not affect the vast majority of software. But do keep in mind that there are slight compatibility issues between official ZX Spectrum models.

What kind of keyboard and case do you have in mind? I don’t know about now, but new rubber key cases were being manufactured a couple of years ago, along with new keyboard mats. Replacement (new) membranes are available. And the PCB mounting connectors are available.

Mark

[8008guy]

Hi,

That's helpful.

On keyboards I see the ones at sellmyretro. I'm a newbe to the spectrum. Visually the plus and 128k have a different layout than the 16 and 48k keyboards. Electrically are they compatable? Is there a high quality keyboard available?

Len

[1024MAK]

The original “rubber key” 16K and 48K models uses a 40 key keyboard matrix. This uses eight “output” lines (actually the processor address lines A8 to A15 via diodes) and five input lines (which go to the ULA chip). Hence 8 x 5 = 40 keys maximum.

The ZX Spectrum+ uses the same PCB designs as the “rubber key” models. So Sinclair came up with a novel way to add the extra keys. Instead of using a membrane with two conductive layers, they used a membrane with four conductive layers. So when you press one of the extra keys, electricity two different sets of contacts are being pressed. The ROM code detects this in the same way that it detects a user pressing two keys at the same time.

The ZX Spectrum 128 uses a different case, but the same membrane as the ZX Spectrum+.

The best quality keyboards on official ZX Spectrum machines were the Amstrad made +2 (grey), +2A (black), +2B (black) and +3 models. They use keyboards similar in feel to the CPC464 and CPC6128 machines. Note that these keyboards are not fully compatible with the earlier models or the Harlequin. The tails of the +2 are different and the matrix is very different on the +2A, +2B and +3 machines.

In the 1980s there was a large market in third party keyboards to replace the rubber key keyboard. Some are still traded on auction sites and other second hand trading places.

Occasionally someone will make their own keyboard using a new PCB and currently available keyswitches and standard caps. But these are often expensive and only made in very limited numbers.

Mark

[8008guy]

Thanks Mark,

I'll keep my eyes open for a suitable keybord.

Len