COSMAC ELF Group Guidelines and FAQ

The COSMAC ELF group on is a public discussion forum for all manner of topics related to RCA's CDP1800 “COSMAC” series of microprocessors, most popularly the CDP1802. The group has been around since spring of 2001, moved to Yahoo at the end of 2001, and moved to in March of 2019.

While the group is generally self-policing and needs little in the way of moderation, this page suggests a few loose guidelines and answers a few recurring questions. Thanks for giving it a read, and please enjoy the forum!


Be kind. Be respectful. Mentor. Learn.

The written word lacks the nuances of face-to-face conversation. The occasional smiley can give a hint that something isn’t to be taken too seriously, while TYPING IN ALL CAPS can be misconstrued as shouting — even though it may have been intended just for emphasis. It’s okay to shout CMOS or DMA or COSMAC around here, though. :)

People sometimes hold strong opinions that will differ from yours; they will make mistakes or say something insensitive. Disputes happen. Exercise patience and empathy. Be quick to forgive, and quick to apologize.

Personal attacks have no place here. If you feel angry, it’s the wrong time to type a post; try going for a walk instead. Failure to abide by this may result in future posts being moderated, or, in extreme cases, a ban from the forum.

Click here to report problems.


Got a great new COSMAC system up and running, or a shiny new CDP1802 C compiler? Did you unearth a bit of history about how RCA brought about the first commercial CMOS microprocessor? Have any tales to tell about debugging in the light of lava lamps or wirewrapping your first ELF? Got questions about SCRT? This is the forum for you!

Please keep in mind that everything posted to the forum arrives in hundreds of email inboxes around the globe. Each of those inboxes belongs to someone who subscribed because of an interest related to the CDP1802 or the old computing equipment built upon it. Try to keep posts somewhat on-topic: that's the content people subscribed for.

What constitutes an on-topic post is subjective. Some level of tangents and personal asides is not only natural, but adds spice to what could otherwise be a dull and antisocial forum. Conversations that veer too far off course for too long might best be moved to personal email exchanges, however.

Threads can get long, and sometimes some previous messages need to be quoted to provide some context. But please trim quotes down to just what is necessary.

Avoid foul language; it’s unnecessary. Politics, religion, and sea cucumbers have better forums for discussion on the web. Uncle Bob’s timeshare or an Easy Way To Make $8,000 Per Day From Your Bathtub shouldn't be advertised here. And porn rendered with Pixie graphics is just sad.

Click here to wake up the moderator or report inappropriate content.


In one perfect world, every piece of software, every publication, and every photo would be free for everyone to use, build upon, and republish. In another perfect world, everyone who wanted recognition or compensation or creative control over their work would receive it, and there would be no software piracy or loss of revenue. This is not a perfect world, however, let alone two contradictory perfect worlds. The ugly balance between the rights of consumers and content publishers lies in the purgatory of copyright law.

This isn’t a legal document by any means, and I have no background in law, but in general I think a few common sense guidelines will suffice for this FAQ.

Most obviously, don’t post someone else’s work without permission unless it is truly in the public domain. Whether a program or a scan of a commercial magazine article, it shouldn't be uploaded to the group’s file area unless approved by the copyright holder. Make a sincere best effort to secure such permission; it will pay off surprisingly often.

If you find something freely available on the web and want to keep a copy on your hard drive for personal use, that should be fine, to the best of my knowledge. The trouble comes if you republish copyrighted information without permission to do so.

Generally it is considered fair use to quote brief excerpts of a copyrighted work to make a point. There are probably entire books devoted to explaining what constitutes a “brief excerpt” and the myriad of twists on what constitutes fair use, and I never hope to read any of them. Publish something original, or something in the public domain, or something with express permission, and you won’t run afoul of copyright law.

Click here to report copyright violations.

Quest Electronics Copyright Information

Forum member Steve Gemeny tracked down the former owner of Quest Electronics, Roger Pitkin, to determine what rights might be granted to the hobbyist community. Roger graciously allowed that Quest Electronics materials may be released with a Creative Commons Non-Commercial Share and Share Alike watermark and attribution to Roger Pitkin. Anyone can now freely publish Quest Electronics information under those guidelines, as long as it is not sold. The community owes Roger a debt for his generosity, and Steve for his efforts to secure his permission.

Thanks also to Steve Brune for scanning and providing the Questdata newsletters.

For further details on the requirements for publishing Quest Electronics materials, please see the group's Files section.

RCA Documentation Copyright Information

Doug Balog of Intersil’s legal department granted permission to publish CDP1800 series data sheets on April 3, 2001, under the condition that it was clear that the site had no affiliation with Intersil and makes no representations about their products.

On July 1, 2013, Paul Bernkopf of Intersil’s legal department authorized some additional permissions with the following email: “Subject to (a) you not removing any copyright or other IP ownership labels, (b) subject to Mr. Balog's prior requirements, and (c) to the extent Intersil Corp. and its subsidiaries (‘INTERSIL’) has the right to grant permission, Intersil authorizes you to reproduce the documents cited below on your website.”

The documents referred to in the aforementioned email were:

  • “Operator Manual for the RCA COSMAC Development System II CDP18S005”
  • “Evaluation Kit Manual for the RCA CDP1802 COSMAC Microprocessor”
  • “Fixed-Point Binary Arithmetic Subroutines for RCA COSMAC Microprocessors”
  • “Floating-Point Arithmetic Subroutines for RCA COSMAC Microprocessors”
  • “User Manual for the CDP1802 COSMAC Microprocessor”
  • “COSMAC Microboard Computer Systems” (appears to be a flyer of some sort)
  • “Microprocessor/Memory Applications Briefs - A compendium of the most useful CDP1800 Series microprocessor/memory application hints that have appeared in recent issues of the RCA Solid State Newsletter”
  • “RCA COSMAC VIP Instruction Manual for VP-111”
  • “COSMAC Microprocessor Product Guide” (seems to be catalog of sorts with abbreviated data sheets)
  • “RCA COSMAC Microboard Computer CDP18S601” (flyer)
  • “COSMAC Floppy Disk System II” (flyer)
  • “COSMAC Development Systems CDP18S005, CDP18S007V1, and CDP182007V3” (flyer)

Frequently Asked Questions

Some questions seem to come up again and again; some others we’ll pretend are asked often to take up space until a better set of questions evolves. Here’s a random sampling:

Where can I buy an 1802-based computer kit?

Lee Hart offers a tiny, inexpensive computer called the Membership Card, which lets you toggle in and run programs just like the original COSMAC ELF. The whole assembled computer fits inside an Altoids mints tin. Buy the bare board or a full kit directly from Lee. Herb Johnson also offers extensive documentation of the Membership Card on his website.

Which spacecrafts used the 1802?

There’s been a good deal of misinformation on this topic, but Herb Johnson researched the topic extensively, and answered the question thoroughly, on his retrotechnology website. Galileo used the 1802, as did several other satellites, but Voyager and Viking did not. Visit Herb’s page on the subject for the full story and numerous interesting links.

Who was Joseph Weisbecker?

Joseph Weisbecker was the engineer, inventor, and author who created and evangelized the CDP1800 COSMAC line of microprocessors for RCA. Biographical information on Weisbecker can be found on the Vintage Computer Wiki and the COSMAC ELF website.

Where can I learn about programming the 1802?

One of the best tutorials on 1802 programming is available freely online: A Short Course In Programming by Tom Pittman. Thanks to Tom for making this available, and to Lee Hart for translating the work to HTML.

Another excellent book is the Programmer’s Guide To The 1802 by Tom Swan, which may be purchased in PDF form directly from the author. Please support the author and do not share your copy of this book online.

Finally, if you have questions, just ask the group! We have plenty of experts who’d be happy to lend a hand, and beginners are always welcome.

How can I email other members?

When using the Yahoo group via Yahoo’s website, bear in mind that email addresses embedded in messages will automatically be truncated. Yahoo does this to keep email addresses from being scraped for various purposes, such as scams or mass marketing. Attempting to send someone your email address through the group will only work if the receiver gets group messages via email. If you want to post your email address to the group so that anyone can see it, either provide an indirect reference (i.e., “find my email address on the About page on [some personal website]”), or express it in a format that Yahoo won’t replace (such as “dave -at- ruske -dot- com”).

What if the forum becomes inaccessible? Is there a backup?

Forum content is occasionally archived here. This isn’t too polished, and not intended to replace the forum in any way, but it serves as protection against the content being lost.

Why Why not something else? replaced Yahoo in March 2019, providing an easy-to-use message board that allows use via web or email, and also gives us a reasonable file storage area, photos, even a Wiki. Some reasonable spam filtering is in place that eases moderation, and servers are professionally managed and patched against attacks.

© Dave Ruske 2001-2022, except where noted