Will these SIMMs do for an NMS 8250 memory expansion?

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By Turrebo

Expert (82)

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12-10-2012, 16:52

I recently acquired an unmodified NMS 8250. I'd like to expand the RAM a bit, and I'm not affraid to handle the solder iron (I successfully chipped a PlayStation2, those IC contacts are really tiny!).

Problem is: I do have some 72-pin SIMMs, but I have no idea if I can use them in my MSX. They contain the following memory chips:

VG2618165BJ (42 pins)
HY514404A (20 pins)

Any thoughts on this? Your input is greatly appreciated!

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By OeiOeiVogeltje

Paragon (1426)

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12-10-2012, 17:00

i believe you can find infot on that on the hans otten site
it should be a 30 pin sim iirc

By Jipe

Paragon (1594)

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12-10-2012, 17:08

By RetroTechie

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12-10-2012, 17:18

Those 42-pin IC's are probably not usable. Those 20-pin IC's are most likely 1M * 4bit DRAMs, so 2 of them would give 1 MByte.

But hooking them up isn't straightforward (I used a small circuit board back in the days, to produce extra address / refresh signals). And you'd put 15+ year old RAMs into your machine as expansion, that's asking for trouble TBH.

For 512K or 1MB, I'd consider using 512K * 8 bit SRAM. Buy new (about 7 Euro / piece), piggyback on top of a ROM, relatively easy to wire up & no problems with memory refresh.

By Turrebo

Expert (82)

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12-10-2012, 19:10

Je, tu, il, passé composé... That's all the French I know (my bad, I didn't pay attention in school) . But maybe Google Translate can help me out there. It certainly looks doable. A lot A bit Easier than a PlayStation2 anyway.

I used to have an NMS 8250 with added RAM (128KB extra), but I remember it being on a separate board with a bunch of wires connected to the main board.

Hmmm... I will consider the French connection ;) . In the mean time I will check out Hans Otten's website, see if I can learn more about memory expansions.

Thank you all for your input!

By Turrebo

Expert (82)

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15-10-2012, 08:20

Sorry to bother you again, but I had a look around and I have some more questions regarding upgrading my 8250's memory.

For most internal upgrades you have a grand choice of three alternative memory types: it's either a 30-pin SIMM (which I can obtain for a few €€€), an SRAM (can't find a clear step-by-step plan for mounting it) or the famous 41464 IC, which looks a bit more work but very straightforward to fit.

RetroTechie has some doubts about using a 15yo memory bank (i.e. the 30 pin SIMM) as an expansion, so I thought I'd go for the 41464 option.

All the necessary ICs are, amazingly, obtainable from online shops, except the actual memory IC itself.

Questions: Where can I get twelve 41464 ICs, are there any alternatives for the 41464 that I can order in a webshop, and does somebody (RetroTechie perhaps) have a step-by-step plan for mounting an SRAM, just in case (preferably in English, Dutch, or, if that fails, German)?

Thank you very much so far!

By Jipe

Paragon (1594)

Jipe's picture

15-10-2012, 11:47

http://www.hansoranje.nl/
look at NMS 8250/55
is the good way for you ;)

By RetroTechie

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15-10-2012, 13:09

Turrebo wrote:

RetroTechie has some doubts about using a 15yo memory bank (i.e. the 30 pin SIMM) as an expansion, so I thought I'd go for the 41464 option.

And how old you think those RAM chips are? LOL! All 5V compatible DRAM chips were produced before 1995 or so, New Old Stock (stored, not used) is the best you can get but still old. Which is a problem specifically for memory chips because failure of 1 single memory cell makes the entire memory chip bad.

Using 4464's is no good in that light as you'd solder high stacks of them. Then when there's a problem with a chip on the bottom of a stack, what are you gonna do? Good luck... Evil

Better is to use the smallest # of chips that will fit the memory size you want:
256K*4 for 256KB or 512KB
1M*4 for 1MB or 2MB
4M*4 for 4MB (and/or 2MB, switchable)

Then you have to deal with DRAM refresh, which is another story entirely.

SRAMs sidestep a lot of these issues. Back in the day these were expensive which isn't an issue anymore. How to wire up? Check the "Read Me" for this project, it's really that simple.

Obtaining the expanded address lines is basically a matter of wiring up additional datalines, similar to how D0-D2 are used in the NMS8250's mapper circuit. Most 'difficult' IC you need is a 74HCT670 (or LS670).

By Turrebo

Expert (82)

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15-10-2012, 15:16

Ok, thank you for pointing that out. I never knew there was so much to installing RAM in a 8250... I will read your suggested document tonight.

Despite all these challenges, I'm still looking forward to get cracking! More so, in fact. Maybe I'll learn a thing or two in the process.

I'm so glad I have an MSX again, it was one of the highlights of my youth. I'm having the time of my life. Again!

By Turrebo

Expert (82)

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22-10-2012, 12:26

Sorry for the topic kick, but I have an additional question.

Due to the lack of 41464 and/or compatible ICs and the complicated nature of the SRAM option (sorry RetroTechie, 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 ;-) ) I've decided that installing a 30-pin SIMM is the best option for me.

The installation instructions are very clear, every IC is available from stock, and I even found a website where you can order a 4MB 30-pin 3 IC SIMM from stock, for less than $4,-

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

Thank you very much for helping me making up my mind!

By OeiOeiVogeltje

Paragon (1426)

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22-10-2012, 17:20

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

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