Jump to content
joethezombie

IIfx 16MB SIMMs -- Thanks Doug!

Recommended Posts

I ordered my boards through seeedstudio, because I had a pretty good coupon from a previous project.  But ALLPCB will send you 20 boards for $56 which is still a bit cheaper than what I spent for mine.  As far as chips, I spent $34.99 for a pair of 64MB modules on eBay, which had enough chips to make 9 completed SIMMs.  All in all, a bit shy of $7 per SIMM.  Not too shabby!  I have two IIfxs to populate, and will need a couple more 64MB modules to complete the set, which will leave me with 2 spare SIMMs and 2 bare boards in case of a failure.  So far, I've only built up the 4 shown, but they pass all memory tests I've tried.

 

I do feel bad for pillaging the chips from working modules.  If I were to make a lot of these, I would certainly try to find a supplier of bare chips.

Share this post


Link to post
Share on other sites

Yeah, nothing in stock unfortunately.  There is a seller on ebay with a whole reel of bare chips, but is listed as "away" for quite some time, and they never responded to inquiry.  There is also the somewhat seedy asian distribution market, but with the few amount I was building, I didn't bother.

Share this post


Link to post
Share on other sites

I kinda assumed, if you were skilled enough to harvest memory chips from one simm for another, and do it where it looks nice, you probably already knew what mouser was.

Share this post


Link to post
Share on other sites

Great work! I'd be interested in getting 8 simms if you do end up making a production run of these. I'm sure here must be some others on here after those SIMMS and have no way of producing their own! 

Share this post


Link to post
Share on other sites

I have access to some of these chips, TI TMS416400DJ - would these work?  I checked out the spec sheets and the pins were almost the same between these and the ones listed as working:

M5M416100BJ

KM41C16000BK
 
There are some minor differences, but I'm not anywhere near fluent enough in reading these to tell if they are important minor differences.
 
By the way, those are some terrific boards - nice job!
Edited by Juror22

Share this post


Link to post
Share on other sites

Awesome! I like the color you picked :)

 

Also, I have to give kudos to trag for his original research on IIfx RAM which you can find on this site in various threads. His info was very valuable as I was designing the PCB.

Edited by dougg3

Share this post


Link to post
Share on other sites

Indeed, trag's posts are what led me to your design so I have both of you to humbly thank!   You guys are awesome!

 

@Juror22, I don't think those would work.  They appear to be 4Mx4bit chips.  Maybe they would work with trag's alternate 2-chip design that used a couple of bidirectional switches?  Not sure.

 

@TimHD, I'm not planning on making anymore unless a bunch of raw chips happen to fall in my lap.  It takes time to find the modules at a reasonable price on eBay, and even more time to remove them, and I don't have a lot of that.

 

But there is a gentleman over on mac68k.info that has secured a bunch of chips and has even boards.  I'd been watching for him to make sets or even kits to sell, but after two years of waiting, and no response to private email, I figure it's not happening and made my own.

Share this post


Link to post
Share on other sites

Shouldn’t 16Mx4 work as well? You will only need two chips that way. I was thinking about getting a few 30-pinners done with chips from 64MB 72 pin SIMMs I don’t need anymore.

Those will also be low profile enough to fit well into SE/30s with only two chips.

Getting two 64MB SIMMs + having blank SIMMs manufactured cheaply will also cost less than buying 128MB worth of 30pin SIMMs from memorymasters and the like.

 

I might look into that. It was always tempting to max the RAM on my WGS95 }:)

Share this post


Link to post
Share on other sites

It'd be nice if 16Mx4 did work, even if such chips still aren't available via Mouser. And https://68kmla.org/forums/index.php?/topic/21519-finally-a-iifx/?p=221669 mentions a prototype involving paired 16Mx4s, a pair of FET bus switches (identified as SN74CBT3244 or similar), and a "five-pin gate" (probably an SN74xx1G series two-input of some sort)... But that they're finicky.  Given the theory that the use of fewer chips is causing ringing on the address lines due to reduced load from the chips themselves, I was wondering if a set of fairly stiff pull-downs might help, but this is definitely beyond where I'd trust my intuition.

 

Hrm... 1Mx16 is available. That can be run as 2Mx8, since it has separate "upper" and "lower" CAS pins. Still 8 chips, plus glue, but if it can be made to work then sourcing components becomes straightforward.

Share this post


Link to post
Share on other sites

16M X 4 does not work, because the IIFX SIMM needs separate read and write data pins for each bit.  On the X4 memory chips, the read and write data pins are combined into one bidirectional pin.    I was able to work around that as described in the posting that nyef linked to.

Share this post


Link to post
Share on other sites

Maxing out a IIfx with RAM is like maxing out a Q950, its cool but nothing you would run on that system/processor would need it. The other issue is even 4MB SIMMs are getting hard to find, so if you are going to have to build your own you might as well go 16MB.

Share this post


Link to post
Share on other sites

I did not know the other thread, otherwise I would have not brought up that topic.

I was just throwing in the idea as I am building a few 30pin SIMMs using 16x4 right now. I figured IIfx SIMMs are 8bit as well so there it went :p

Edited by Bolle

Share this post


Link to post
Share on other sites

Bolle, were you active on a French language Macintosh site?  Something like Macboudille or some such.  Unfortunately, I've never studied French, so apologies in advance.   There was some nice hacking discussion there.  I can't seem to find it now.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×