This is kind of an odd topic, but it’s something worth checking out. Let’s make it nice and simple. You’re looking for the JEDEC standards for RAM, ROM, EPROM, EEPROM, Flash, etc. It might be pinout information or programming command sequences that you want to find. Where do you go to find it?

You go to JEDEC, of course. The problem is that JEDEC’s site is kind of confusing to follow. The first thing you need to know is that the standard for memory is called JESD21-C. You can order a hardcopy, but you really don’t want to do that. You just want a PDF, right? Well, you’re in luck — sort of.

JEDEC provides the standards for free download (as long as you register — no big deal), except they break it down into tiny sections. On the JESD21-C site, you can find download links to the Table of Contents, Terms and Definitions, General, Applicable Other Documents, and Differences between revisions. These are mostly summary things, but the table of contents is the most useful part. If you download that, you can find a list of everything JESD21-C has to offer. Section 2 — Terms and Definitions — is also very helpful, because it gives you some definitions you might need to know for pin names. Notice that sections 4 and 5 are not links. That’s where all of the important information lives! How are you supposed to get there? Keep reading.

Once you’ve discovered which standard you need in the table of contents (typically in section 3 or 4), you can find it by looking in the correct category under the sidebar on the right called “JESD21-C Standards”. Click on the section containing the standard you want, and a list of all standards belonging to that section will come up. Find the correct one and, after logging in, download it!

It’s great that JEDEC provides all of these standards for free download. I do honestly think it’s a bit annoying that they break it up into tiny sections though. Why not offer one huge PDF containing it all? I guess you could manually download every document and use a PDF editor to combine them all into a single PDF if you want.

Example search:

I’ve been using the SST39SF040 in my programmable Mac ROM SIMM project. I know that the datasheet for the chip contains everything I need to know, but I was curious about what the standard had to say. The SST39SF040 is a 4 megabit (512K x8) flash chip. In particular, I’m using the variant that comes in a PLCC32 form factor. It doesn’t have a separate VPP programming pin — the only power supplied is through VCC. This means it’s a “single supply” chip, as opposed to a “dual supply” chip. Although it’s sectored flash rather than byte-erasable EEPROM, the info about EEPROMs still mostly applies.

So first of all, I find the section on EEPROMs — section 3.5. In addition, I know it’s a byte-wide chip (x8), so I know I’m going to be looking under section 3.5.1.

Next, I just skim all of the sections underneath 3.5.1 until I find section — 128K to 512K by 8 Single-Supply EEPROM Family in DIP RCC and TSOP1. That’s the one I need! (RCC is pretty much another name for PLCC in this case) So I download the JESD21-C section 3.5.1 document from JEDEC’s site, and sure enough, there’s the pinout — and it matches what the SST39SF040’s datasheet says. The only really noticeable difference is that JEDEC uses the terms E, G, and W in place of the more-commonly-seen CE, OE, and WE. This is all explained in the Terms and Definitions document, though.


I hope this helps someone else out there who is trying to navigate the JEDEC specs. There are a lot of them, but once you know where to go on JEDEC’s site, it’s not too bad.


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