Figuring out old Russian memory chip 185РУ3

Description

I've been trying to figure out this odd old 64 bit SRAM chip. It's 64 bit in that it can hold exactly 64 bits. Me eventual plan is to put 8 of them on a board and make possibly the worst memory module ever with 64 bytes of storage.

I've run into an issue though, like many old Russian datasheets it's not super clear. I've tried connecting it up but no matter how I set the address pins and toggle the write pins the output never goes low (it's open collector). The chip has 2 input pins 0 and 1, I'm not sure if it has the memory separated into two banks set with their own data in pin or if one pin sets the selected address to 1 and the other sets it to 0. I assume the later since there is no separate pin to tell it to latch whatever is on the data pin.

Details

I'll post photos of the test setup I have.
Currently I have the 6 address lines set up to dip switches with pulldown resistors. I have each data in pin connected to a button with a pulldown. The chip has an internal resistor I assume is used as a pullup for the open collector output. I've tried the output with the built in resistor and with an external 10k pullup. There is a microswitch connected to the CS pin in the picture to see if enabling and disabling the chip would make any difference but it didn't.

I made an adapter to make connecting the old Soviet designed chips easier. If anyone is interested I can post the files for that.

If anyone comes across this and has any ideas on what I may be doing wrong or knows who to ask about this kind of thing please let me know. If I manage to figure it out I'll update this project and get a tiny memory module made and connect it to an Arduino.

I also delidded one and took a very crappy die shot with my phone camera and the eye piece from one of those kids microscopes. One of these days I'll get one of those USB microscopes. I think it's interesting anyway.

Discussions

Tyler Bourne wrote 08/19/2021 at 00:52

I've got the chip working! First go around was my inexperience with TTL and the second issue was a loose chip select wire. Want to thank hartl and Ken Yap for the advice.

Now I'm going to put 8 of these on a board and make the crappiest memory module! I collect vintage display technology so it will probably end up used in something like that.

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Ken Yap wrote 08/19/2021 at 01:57

Well done. BTW you didn't need DT switches for the D1 and D0 lines. It's actually simper and better to pull up the pin through the resistor and use the switch to ground it. That way there is no time when the pin voltage could be undefined during the switch transition. Although there will still be contact bounce.

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zpekic wrote 06/21/2022 at 21:51

So is it actually more like 64 S/R (set / reset = 0/1 inputs) flip-flops in the chip than a classic 64 D-type flip-flops? Seems the R output is already one prepared terminal for the 3-4k pull-up resistor.

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Ken Yap wrote 08/16/2021 at 22:45

Could you provide a schematic of your test setup, even a hand drawn one? Better than trying to describe it in words.

Also have you tried getting Google Lens to translate the datasheet?

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Tyler Bourne wrote 08/18/2021 at 02:54

I've added one to the image gallery. I suspect the issue might be with the D1 and D0 inputs but I'm not sure.

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Ken Yap wrote 08/18/2021 at 03:03

You're asking the output to sink about 10mA through the LED in the low state which may be too much. Use a transistor buffer.

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Tyler Bourne wrote 08/19/2021 at 00:28

I'll up the resistor value. It should be able to safely sink 6ma and the LED should be plenty bright with that.

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hartl wrote 08/15/2021 at 05:24

This is TTL where inputs source >1mA, 10kΩ pulldowns won't work. Try connecting the inputs with resistors to Vcc and switches to GND. The output should be able to drive a LED+470Ω to Vcc.

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Tyler Bourne wrote 08/15/2021 at 13:23

Thanks, I thought it must be something like that. I'm too used to modern CMOS ICs.

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Tyler Bourne wrote 08/16/2021 at 19:28

I changed it around but it's still not working. Maybe an issue with the switches on the D1 and D0 inputs? I have them connected to microswitches so normally they are grounded but when I press the switch it is connected to 5v through a 10k resistor.

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Mike Szczys wrote 08/13/2021 at 15:50

Looks like a fun puzzle to solve, can't wait to follow along!

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Figuring out old Russian memory chip 185РУ3

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Figuring out old Russian memory chip 185РУ3

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