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I've put tiny stickers on in place of the missing overlay.
Sorry Sascha2000; I didn't mean to interrupt and monopolize your thread. It only took a very short time with my new toy to be able to see your motivation in creating the multi-ROM. It would be so very cool.
No problem, really! (I have put this thread anyway in the wrong area of the forum. )
To see the pictures of your machine is a big pleasure, I think not only for me.
So please go on!
@sirmorris: Wouldn't it be possible to use the zxpand in conjunction with the multirom in the lambda? I mean something like an adapted zxpand-rom for the Lambda burned in the eprom...
the multirom now works on a ZX81 well too.
Following limitations exists::
* The Forth Rom + Assembler ROM won't work together with Karls 32K Ram expansion. thats cause of his 32k intit circuitry.
* Genereal every expansion that modifies the internal ROM during runtime or switches it off will not work.
* ZX-Pand won't work, cause it switches the internal ROM mostly off.
* The PCB only fits in a Lambda if the original socket is unsoldered, the 27512 Rom is directly soldered on the multirom + the case of the lambda is changed. I have not test this but it seems to work. However I suggest not to do the same.
* Alternatively I suggest to use a flat cable + special sockets like shown in the picture below. I will give the information where to obtain the same for some €.
* The reset pulse to savely change the roms must last 1sec.
The mods on the ZX81 are not too big (Like on the Lambda).
To change the boot rom the keys 1, A, Q + reset have to be pressed by the user.
On some ZX81 computer the 8th Rom does not work (pressing 1 + A + Q + Reset). I won't investigate this, 7 Roms should in my opinion be enough.
Here you can see a prototype setup of the same:
1 --> Fiffy implementation of a Reset switch. Will be connected to the modulator case for reset.
2 --> Reset Leitung taken from the expansion bus. Can also taken from other places of the ZX81 board.
3,4,5 --> Connectors for 1, A and Q from keyboard.
3,4 and 5 are soldered here: 2 the reset I have soldered here:
I have finished the layout now and will test it the next days. If it has no bug I'll probably go into production. Price I can tell when I know the number of PCBs. I won't earn on this one cent, so they will become more or less cheap.
I will not solder the PCBs (exceptions may be there, but it will last very long until they are finished).
Current 13 PCbs are preordered. If no additional order will come in, I will produce 20 pcs.
If anybody else wants a multirom please send me a pn or write it here in the forum.
ROM images, burned Eproms + GALs I will provide of course on demand, for the prices like thos chips can be obtained at reichelt.de