VOGONS

10ns 32KByte DIP28 cache modules for 386/486 PCs

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First post, by Tiido

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I'd like to pimp out my 386 and 486 machines but 10ns 5V DIP chips are no longer made and other options that involve ebay are either pretty expensive or likely getting you 15ns chips remarked as 10ns... So I thought about making my own and I figured there will be others who would like some too.

CacheModule.png

These will fit nicely in DIP28 footprint and shouldn't damage any sockets on insertion either. Ideally one would permanently solder these to a board for best performance. All modules have a 1µF decoupling capacitor, the footprints on the image show a random part with right sizes, only one will be populated depending on what is cheapest for the time being. There's a huge shortage of these parts so the prices and availability vary a lot.

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Next month when I am no longer broke I'd like to make a load of these cache modules and the cost pretty much depends on how many get to be made. I will want a number of guaranteed buyers and I don't want to make many excess modules. Here are the numbers per module when certain number of modules get made total :

For 50 modules, price per one is 6.00€ (not worth it)
For 100, price per one is 4.00€ (not good either)
For 250, price per one is 3.00€ (kind of decent)
For 500, one will cost 2.50€ (very decent)
For 1000, one will cost 2.40€

There won't be any further decreases, work worst will dominate and there are no price breaks on the most expensive part to give any significant reduction either.

I imagine most people will want 4+1 or 8+1 chips, and possibly two or more sets to pimp out multiple computers. I personally will need 5+9+9 modules and possibly few more for some future boards I'll get my hands on.

I will not be making 128KB ones, the chips all got much bigger footprint and will not fit within DIP size. Parts themselves are also much more expensive.

For contacting by random people who don't want to register here, my e-mail is tmeeco@gmail.com. Use "Cache Module" or something else that will relate to these things in the title.

Last edited by Tiido on 2018-09-11, 14:22. Edited 1 time in total.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 1 of 6, by luckybob

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As someone who say the inception of this project, where are the pins that go into the dip socket?

It is a mistake to think you can solve any major problems just with potatoes.

Reply 2 of 6, by Tiido

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They're under the board, soldered on similarly to what is seen on this pic : http://www.tmeeco.eu/BitShit/PCschit/HeaderExperiment2.jpg

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 3 of 6, by stamasd

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This is a nice project and you have my moral support. I am however not on need of 32kx8 chips as a few years ago I managed to snag on ebay a large lot of them from a business that was being liquidated so I'm set for the next 10-20 years. 128kx8 modules would be interesting though.

( and yes I have offered in the past to help others with cache chips at basically my cost or even below; there were a few takers)

I/O, I/O,
It's off to disk I go,
With a bit and a byte
And a read and a write,
I/O, I/O

Reply 4 of 6, by amadeus777999

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Simply awesome.

Definitely interested - 25 to 50 pieces depending on the price... would be cool if a 1000 could be made. Maybe inform people on other forums as well...
Can one also acquire some adapters with legs but without the 10ns sram? I would like to build a few 8ns ones.
Which vendor's srams in SOJ format would you buy or have you bought?

Reply 5 of 6, by stamasd

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There are 128kx8 memory chips in SOJ package that I think would be mechanically compatible with an adapter like this one, and don't cost an arm and a leg... for instance https://www.mouser.com/ProductDetail/IS ... tlaaITA%3d datasheet https://www.mouser.com/datasheet/2/198/63LV1024_L-258513.pdf
per the dimensions in the drawing they would be at most 8.51mm wide which compared to a skinny DIP package such as this http://www.analog.com/media/en/package-pcb-re … 81510_I_N28.pdf is only about 0.25mm wider. They also cost less than $2 a piece in any quantity over 10.
Those are however 3.3V parts. There probably are 5V parts somewhere too.
(edit) https://www.mouser.com/ProductDetail/IS ... oWXNivQ%3d 5V 12ns $2.09 in multiples of 100

I/O, I/O,
It's off to disk I go,
With a bit and a byte
And a read and a write,
I/O, I/O

Reply 6 of 6, by Tiido

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10.16mm is the absolute maximum witdh for the module (PCB edge to PCB edge in the sockets) and that particular SRAM is a wide type which is exactly that and will be exactly that without any clearance left between chips or the PCB edge, IS63LV1024L-10Jxx would be the thinner type that will fit the footprint and which could work mechanically. In addition it is 3.3V only part without 5V tolerance and will definitely fail in a 386 and will fail on most 486 boards, exceptions would be ones that run the chipset at 3.3V rather than 5V and lack any VLB stuff. Running a 3.3V CPU is not enough, chipset and VLB will still drive all bus signals with 5V and that will stress all those parts as the SRAMs are burning off all the excess voltage with their ESD protection diodes. In worst case the motherboard will die also.

The 5V part actually is a thinner type now that I looked at the datasheet. I found another suitable 10ns part (CY7C1009D-10VXI)from another distributor that I can use. PCB cost will be a bit higher due to larger size and needing a bit more contacts per module, amount of work remains roughly similar but the SRAM is much more expensive compared to the 32KB part. I did run some numbers and the costs for 128KB modules would be as follows :
50 total, single is 7.00€
100 total, single is 5.00€
250 total, single is 4.00€
Lower numbers are not attractive at all, higher one kind of.

amadeus777999 wrote:
Simply awesome. […]
Show full quote

Simply awesome.

Definitely interested - 25 to 50 pieces depending on the price... would be cool if a 1000 could be made. Maybe inform people on other forums as well...
Can one also acquire some adapters with legs but without the 10ns sram? I would like to build a few 8ns ones.
Which vendor's srams in SOJ format would you buy or have you bought?

I would appreciate some word to be spread, getting more done will help to get costs down from price breaks on the chips. Parts I can buy will be Cypress parts (CY7C199D-10VXI, CY7C1009D-10VXI), they have the highest availability and best cost.

I discovered I made a big error when calculating the numbers in first post, I had a 25 part column in part cost and ended up using it in 50, 50 for 100, 250 for 500 etc. and completely messed up my numbers and I only now saw it when I was calulating the 128KB costs. Unfortunately the numbers became quite unfavorable in lower totals with the corrected caluclations :
50 total, 1 = 6.00€
100 total, 1 = 4.00€
250 total, 1 = 3.00€
500 total, 1 = 2.50€
1000 total, 1 = 2.40€

First post is updated with the corrected figures.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

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