IIFX ram gerber

[johnnyilblasco]

Hi guys,
I recently got my hands on some KM41C16000CK-6 chips. That's enough to build about 64mb of ram. Can anyone help me find the Geber files for the Doug Brown simms?

Thanks a lot in advance

 

[finkmac]

@dougg3 had posted them on mac68k when that was a thing. it seems to have gone down at some point though... the internet archive had a scrape but that's down right now of course.

you can also try these, i had those made and i'm still working on getting some assembled.

 

[Melkhior]

There's a design from Garrett's Workshop as well.

 

[dougg3]

@dougg3 had posted them on mac68k when that was a thing. it seems to have gone down at some point though... the internet archive had a scrape but that's down right now of course.

you can also try these, i had those made and i'm still working on getting some assembled.

The Wayback Machine is actually back up and running in a read-only state right now, so you can find it there, but I'll repost them here so that they have another home that doesn't depend on the Internet Archive. BTW, I just want to point out that my design was based on @trag's original research here on 68kmla where he was figuring out how to use alternative wider chips. He also pointed out that DEC 54-24123-AA 64MB 72-pin SIMMs have the correct chip on them.

A couple of random chip part numbers that should work: M5M416100BJ, KM41C16000BK

 

[johnnyilblasco]

@dougg3
Thank you for your response.
I don’t recommend Garrett’s Workshop RAM because it has capacitors positioned right behind the slot clips, making it difficult to attach.
Thanks again for sharing the Gerber files so the community can benefit from them.

 

[dougg3]

Glad to help! Also you probably already know this, but I'll say it anyway: don't forget to order them as 1.2 mm thickness. 1.27 mm would actually be ideal for compatibility, but I'm not sure you'll be able to find a board house that can do it. I know the 1.2 vs 1.27 discrepancy has been a big source of issues with custom ROM SIMMs being flaky in the SE/30.

 

[johnnyilblasco]

Absolutely, the 1.2mm thickness is essential
I just noticed that I have the KM41C16000CK, not the KM41C16000BK. The only difference seems to be that the BK version is 50ns, while the CK is 60ns. Since the IIfx can handle RAM up to 80ns, there shouldn’t be any issue.

 

[Renegade]

Sorry for the topic hijack, but given that there have been recent attempts to design 30-pin* SIMMs using voltage converters to accommodate EDO DIMM chips, could this approach be transposed to a new design for 64-pin SIMM?

*https://github.com/rigred/SIMMBA-16

 

[zigzagjoe]

Sorry for the topic hijack, but given that there have been recent attempts to design 30-pin* SIMMs using voltage converters to accommodate EDO DIMM chips, could this approach be transposed to a new design for 64-pin SIMM?

*https://github.com/rigred/SIMMBA-16

Not impossible, but unlikely, since it's still buffered DRAM which means you can't use common x16 EDO DRAM chips.

You would need to find 3.3v parts for the particular buffered DRAM that the IIfx requires which are also either 5v tolerant on the inputs or will survive being fed 5v while operating at 3.3v (difficult to guarantee...).

 

[Renegade]

I see, thanks for the explanation.

 

[trag]

20 years ago, this is the place where I had .05" (1.27 mm) thickness boards made. I haven't priced anything there since then.

https://www.advancedpcb.com/en-us/services/standard-pcbs/

 

[SmokelessJoe]

I'm late to the party, but I'm looking to make some of these SIMMs. What capacitors are used? I don't see where the caps are mentioned, but I did just come back from the optometrist so my vision is worse than usual.

 

[ObeyDaleks]

50V 0.1uF. 0805 package fits well

P. S. Lower voltage ones will probably work too, I just didn't see a reason since 50v come in the right size and are dirt cheap. I built 2 sets of 128MB with those and they all work well.

 

[Melkhior]

50V 0.1uF. 0805 package fits well
P. S. Lower voltage ones will probably work too

Probably, but beware the behavior of MLCC capacitors. Voltage derating with DC bias can be really bad.

Here's a cheap 50V, 100nF 0805 datasheet (JLCPCB 'basic' so great for cheap projects!): https://yageogroup.com/products/Capacitors/part/CC0805KRX7R9BB104 Select "Capacitance change vs. voltage bias". At 5V you get almost 100nF still, but at 40V you'd be at about 60nF. Devices in smaller packages tend to fall faster, and those with lower voltage rating do as well.

Edit: just for a cheap scare, a 22 uF, 6.3V MLCC in a 0402 package... https://product.samsungsem.com/mlcc/CL05A226MQ5QUN.do. At 5V you get about 2.2uF - yes, that's -90% capacity. Large capacity and small package don't play nice.