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LIV2 / GottaGoFastRAM

8MB Autoconfig FastRAM for Amiga 500/1000/2000/CDTV
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Micron MT4LC4M16R6 #13

Open RetepV opened 2 months ago

RetepV commented 2 months ago

I was checking out alternatives to the ram chip, because I would rather buy it from a trusted supplier than ALI Express (no trusted suppliers seem to carry the suggested memories).

According to the datasheet, the Micron MT4LC4M16R6 ram chip could also be used.

Did anyone try that?

Note that there are 2 versions of the MT4LC4M16:

  1. MT4LC4M16R6 is 4Mx16 with 4096 bytes refresh cycle
  2. MT4LC4M16N3 is 4Mx16 with 8192 bytes refresh cycle.

I would bet that the N3 version will not work without changes to the CPLD firmware, so make sure to get the right version: R6.

LIV2 commented 2 months ago

I believe that just about any 3.3v DRAM with a geometry of 4096x1024 should work

Where can these be purchased? I also dislike having to purchase ICs from Aliexpress or eBay

RetepV commented 2 months ago

Hi LIV2, so for the past days, I have been looking around for suppliers of these kind of ram chips, but they are very thinly spread. The ram chips themselves are obsolete and no longer manufactured, I think. I found one supplier that's a normal webshop:

https://www.westfloridacomponents.com/IC681APH02/MT4LC4M16R6-5F+4M+x+16+EDO+DRAM+CMOS+Memory+IC+Micron.html

But I think the cheapest option is to search EBay for "32MB edo ram". EBay will return a huge list of results. And then scroll through the list to find 32MB simms with 2 ram chips on either side (not 4 on one side, they are most likely TSOP32 versions with multiplexed data/address buses or something, didn't really care to find out myself). These most likely contain four of the 4Mx16 ram chips that we need.

Like this one: https://www.ebay.nl/itm/395007127367?mkcid=16&mkevt=1&mkrid=1346-175129-2357-0&ssspo=I78XqSJoQiW&sssrc=2047675&ssuid=xavr9E77S0K&widget_ver=artemis&media=COPY

Also do a search for "32MB cisco edo". Cisco used 100pin simms instead of 72pin simms, and it seems like all of them use 4MBx16 rams.

https://www.ebay.nl/itm/194205832269?mkcid=16&mkevt=1&mkrid=1346-175129-2357-0&ssspo=85TDKqBITXy&sssrc=2047675&ssuid=xavr9E77S0K&widget_ver=artemis&media=COPY

RetepV commented 2 months ago

I compiled a small list of ram chips that we should be able to use:

Be careful that many of these chips come in a 4096 or 8192 cycle refresh. We need the 4096 cycle version. The 4096 cycle version has 12 address bits A0..A11. The 8192 cycle versions have 13 address bits A0..A12. On the 4096 cycle rams, pin 33 is NC. On the 8192 cycle rams, pin 33 is A12.

This is about all of the information that I can give right now.

Of course, if you want to make these memory board in bulk, you should be able to buy NOS chips through e.g. utsource, or maybe find them with octopart.