albertusj wrote: ↑
Tue Aug 06, 2019 1:16 pm
Has anybody here built the Harlequin ZX Spectrum clone? Is it a very challenging project? Is the board through-hole plated and is it pretty much a case of work slowly and carefully, put everything in the right places and you'll be OK?
If I choose the 128K version, will it be backwards compatible with all the ZX Spectrum 16 and 48K software?
The final dumb question. Do the harlequin fit in a ZX Spectrum case? If I can find one, should I use a ZX Spectrum+ case?
It very much depends on which Harlequin board you get. Harlequin only refers to the scheme. Various people have produced various PCBs, using various PCB suppliers. And there are various versions of the Harlequin design.
The most common 48K version uses mostly through hole components (and has through hole plating), with surface mount components only for the video section.
The boards are fairly straightforward to construct. The SMD (surface mounted devices) should be soldered on first. Then I normally work up through the different height components. Use IC sockets for all the DIL chips. You should carefully inspect the soldered connections every so often, as it is very easy to miss one. Or to find out that what you thought was a good joint, turns out not to be...
Then check again when you have finished. Put all the chips in their sockets, then fire it up
The 48K versions definitely fit in a rubber key or plus case. There are various photos and web pages showing this on the internet. I think that most of the 128K versions also fit.
It’s up to you to decide if you want a rubber key case or a plus case...
In terms of hardware, the designers of the 128K ZX Spectrum made it as compatible as possible with the 16K/48K/Plus machines. Alas, the same is not true of the ROM code. To add the extra functionality, the “spare” space in the copy of the original ROM was used for extra code. This breaks compatibility and hence some games will not run.
Also, you either have to switch to the 48K mode (48K BASIC from the menu or use the SPECTRUM command), or type in PRINT USR 0 [ or RANDOMISE USR 0 ] (and press enter) depending on the game.
In terms of BASIC, the original ROMs (for the 16K/48K/Plus) use Sinclair’s keyword entry system (press just one key to get PRINT all in one go) in an edit ‘line’ at the bottom of the screen, whereas 128K BASIC uses a full screen editor and you type everything in letter by letter. 128K BASIC has some extra commands, but apart from these extra commands runs the same as the original 16K/48K/Plus BASIC (but very slightly slower).
The 128K machines obviously have more memory (128Kbytes of RAM). They also have a AY sound chip. The original Sinclair machines have a DIN socket that has RGB video signals, and using this (with a suitable lead), you get a far clearer video picture. Of course, all the Harlequin boards (48K and 128K) have RGB video signals anyway