Will these SIMMs do for an NMS 8250 memory expansion?

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By Turrebo

Expert (82)

Turrebo's picture

22-10-2012, 17:32

OeiOeiVogeltje wrote:

i tried doing this too (a long time ago)and failed miserably
please document everything you do with clear pictures so i can try again,maybe some day

In what way did you fail? Was your MSX a write-off, or were you able to undo the damage?
What kind of SIMM did you use? I'm still trying to find out if it matters if the SIMM is parity or non-parity.

I'll take pictures of the whole process. It could take a while, though, as I don't have all the information and materials yet.

By RetroTechie

Paragon (1563)

RetroTechie's picture

22-10-2012, 17:45

Turrebo wrote:

(..) I've read the document but the explanation wasn't very clear -or I read the wrong document, knowing me I wouldn't rule that out ;-)

Must assume the latter.. Wink hit page, save .zip, open, click "READ_ME.txt" gets you:

Quote:

The CPLD (Complex Programmable Logic Device) generates expanded address lines MA14~MA18 (5 bits = 32 memory mapper blocks of 16 KB each), for use by a 512K x 8 static RAM. Other connections for the SRAM:

MSX cartridge slot #SLTSL -> #ChipEnable
" " " #RD -> #OutputEnable
" " " #WR -> #Write

Alternative options (which may or may not work) are wiring the SRAM's /OE to ground or to the /CE input. Apart from plugging an external mapper in a cartridge slot, doesn't get any simpler than that I'm afraid. In this case you'd pick up signals internally in the machine and obtain the extra address lines by extending the 8250's mapper circuit (using a 74HCT670 and one or two other IC's).

Quote:

And now the big question: can I install any 4MB SIMM as long as it has 30 pins and 3 ICs?

Very likely. For later SIMM types, there's the issue of FPM vs. EDO, but I don't think that applies to 30 pin SIMMs. The only other thing to watch is access time of the memory chips (and whether they're still 100% good or not). If you use a socket, you could easily swap the SIMM. But directly soldered connections can be more reliable.

By Turrebo

Expert (82)

Turrebo's picture

22-10-2012, 18:55

@Retro Techie:

Thank you for your explanation, I really appreciate that. There is just one minor flaw in the plan: me.

You assume that I have a vast knowledge of phrases like expanded address lines MA14~MA18 and MSX cartridge slot #SLTSL -> #ChipEnable, " " " #RD -> #OutputEnable, " " " #WR -> #Write". I'm very sorry to report that this is not the case. Really, I am. No sarcasm intended.

What I need is a step-by-step plan, like connect pin 1 to point A, connect pin 2 to point B (see picture).

It could very well be that connecting an SRAM is really easy to do, but if so, I need a expanding-ram-for-dummies kind of manual. As stated before, I'm not affraid to handle the soldering iron, but I have to know exactly what to do.

In short: I need practical instructions, not theoretical ones. The fault lies entirely with me. You did your best, but my level is just sub-amateur. Sorry...

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