are slot expanders are dificult to make ? It looks simple to me... some slots on a printboard ...? Ok i'm not a hardware guru... but they look so simple ...
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try to do it yourself.
for example:
http://www.flickr.com/photos/44218601@N06/sets/72157623783899127/
http://www.flickr.com/photos/44218601@N06/sets/72157623908413012/
http://www.flickr.com/photos/44218601@N06/sets/72157623908421876/
.. ok ... that's looks hard to me ..... but if you can make it on a small printboard .. 
.. ok ... that's looks hard to me ..... but if you can make it on a small printboard ..
If you need an printboard then...
A slot-expander is not a simple straight-through of all signal wires. For example if plugged into slot 2, the #SLTSL signal for that slot is converted into 4 #SLTSL signals representing 2-0, 2-1, 2-2 and 2-3 subslots. This conversion (involving a register at #FFFF in the expanded slot) is... well... 'non-trivial', it requires a bunch of logic circuitry. 
internal slot expansion in panasonic wx: http://www.flickr.com/photos/44218601@N06/sets/72157623784027953/
Why? Doesn't the engine in Japanese MSX2+ machines like this allow to expand both slot 0 and 3 (like the S1985 engine) ? Then you have slot 0-0, 0-1, 0-2, 0-3, 1, 2, 3-0, 3-1, 3-2 and 3-3. I know some software doesn't like expanded slot 0, but: if you need a #SLTSL signal to add just 1 specific thing: all the 3-x taken for the memory range you need :-?
Somehow it feels il-logical to add electronics to expand a slot, in a machine like this....
A slot-expander is not a simple straight-through of all signal wires. For example if plugged into slot 2, the #SLTSL signal for that slot is converted into 4 #SLTSL signals representing 2-0, 2-1, 2-2 and 2-3 subslots. This conversion (involving a register at #FFFF in the expanded slot) is... well... 'non-trivial', it requires a bunch of logic circuitry.
internal slot expansion in panasonic wx: http://www.flickr.com/photos/44218601@N06/sets/72157623784027953/
Why? Doesn't the engine in Japanese MSX2+ machines like this allow to expand both slot 0 and 3 (like the S1985 engine) ? Then you have slot 0-0, 0-1, 0-2, 0-3, 1, 2, 3-0, 3-1, 3-2 and 3-3. I know some software doesn't like expanded slot 0, but: if you need a #SLTSL signal to add just 1 specific thing: all the 3-x taken for the memory range you need :-?
Somehow it feels il-logical to add electronics to expand a slot, in a machine like this....
I'm using a cpld that expands slot 2 (pin 4 slot select)
2-1 used with L.Padial SD/MMC (see floppy disk , no disk drive!)
2-3 used with megaflashrom scc, front on/off rom select switch now for this use
2-0 & 2-2 free (external use with 2 x slot cartidge)
My panasonic WX :512k ram, 2xSD/MMC, megaflashSCC, slot 1,slot 2-0,2-2 free, no floppy disk needed.
;)
L.Padial SD / Megaflash SCC doesn't work in slot 0-x 
btw. you could always re-route / swap some slot signals, like move something from internal 3-x to a 0-x slot (if it works there, and another internal expansion doesn't)...
L.Padial SD / Megaflash SCC doesn't work in slot 0-x btw. you could always re-route / swap some slot signals, like move something from internal 3-x to a 0-x slot (if it works there, and another internal expansion doesn't)...
L.Padial SD & megaflash works fine in slot 0-1
and slot 1-0 1-1 1-2 1-3 or 2-0 2-1 2-2 2-3
sinfox has developed a nice MSX slot expander with 1024kB built-in:
I don't know the price. Ask him!: amanohyo (at) hotmail (dot) com