1802, A landmark device in microprocessor history


Page last updated Nov 24 2019. The text below was written by Steve Gemeny, who worked on a number of NASA spacecraft projects at the Johns Hopkins Applied Physics Laboratory (JHU/APL). In Feb 2002, Steve Gemeny discussed some history about the RCA COSMAC 1802 microprocessor, in a Yahoo (now groups.io) discussion group called cosmacelf. He covered his experiences with it as a young man in the 1970's as a kit builder; and again decades later when he shared that same kit with his own teenage son. As a digital designer of US spacecraft, he also discusses the use of the 1802 in aerospace; and researches other critical uses of this processor.

He reposted his remarks from time to time, and I noticed them in July 2011. I contacted the author to get permission to include this discussion on my Web site. I'll pass along to the author any inquires or comments. But also look at the cosmacelf groups.io group, where Steve is active today.

My site supports the 1802, as a kit by Lee Hart called the Membership Card. Check that page for details and more information about the history of the 1802. - Herb Johnson

From: Gemeny, Steve
Sent: Wednesday, February 06, 2002 5:17 PM
To: 'cosmacelf'
Subject: 1802, A landmark device in microprocessor history

Stewart Marshall wrote:
> It is curious and wonderful, the appeal this
> little chip continues to have!

This is really true. Many folks simply don't realize how wide spread the use of this landmark device was.

I too built an elf from the construction article in the late 70s. I was fresh out of high school and wanted a computer in the worst way. I had been shopping for an Altair or an IMSAI but I just couldn't come up with the $500+ . I was thrilled when I saw the first article on the elf and had parts ordered within a week.

My copy of the August '76 PE (now ensconced in a plastic jacket) bares the scars of being well read and annotated during the construction. Over the several months, I upgraded the elf with most of the accessories in the following articles. Finally, being employed full time in the electronics field, I decided to upgrade to the QUEST Super elf. I abandoned the elf and it faded into oblivion and was lost. I have kept the Super Elf, fully equipped with 4 K of ram, the QUEST Super ROM Monitor and Tom Pittman's TINY BASIC, complete with all of the documentation. Presently, My Super ELF is operational running Tiny Basic with the newly assembled (Psudosam 18) IO routines blown into a fresh 2716 at 300 baud into my Pentium 133 running ProComm as a TTY (Oh the irony of it all). But that's not the end of the story...

Being inspired by the on line activity, I have unearthed my 1802 parts from the basement and re-birthed the original ELF on a proper wire wrap board. I have been able to teach my 11 year old son about wire wrapping, memory, Bits, Bytes, Nibbles, Hex and Binary as well as registers and basic program flow.. If only for this, it was worth the effort. But I also have the satisfaction of recreating a significant piece on techno history. (Build your own now while you still can.)

What most people think of when discussing the 1802 is the early video games. Most people do not realize is how significant this quirky little micro processor has been in the space and medical worlds.

As I was pouring through the web, I discovered that the 1802 was the preferred flight microprocessor for dozens of satellites and space based science instrument for over a decade. As recently as 2000, the 1802 was relied upon as the flight processor for the Internal Housekeeping Unit (IHU) of an Amateur Radio Satellite, AO-40 (Ref 1).

But the significance of the 1802 was not limited to the ham radio satellites, Galileo flies with 17 of them on board. Each of the 11 instruments is controlled by an 1802. The Command Data System is comprised of two redundant strings of three 1802s.The 1802 is delivering real-time science data that is in the news NOW! ( ref 3 ) The spacecraft and the quirky little 1802s have survived nearly 3 times longer than the design life and have endured nearly 4 times the anticipated radiation levels. (It's the RAD hard nature of the 1802 as much as the low power that makes it so attractive for space flight.) This is a true testament to the endurance and significance of this little micro to the science community.

But wait... There's more.

I have recently uncovered some documentation in my employer's archive that suggests (I'm still waiting on some of the details to arrive) that the 1802 was the micro of choice for the medical implant community. I have found studies from the early eighties describing this application and highlighting yet another quirky feature of this quirky processor.

It seems that stopping the clock on most micros is bad, since the internal registers are usually dynamic memory. The internal architecture needs a minimum clock frequency to refresh these registers. The 1802 has no minimum clock frequency. The use of CMOS allows the registers to be static in nature and the contents are preserved even with no clock at all. Stopping the clock on an 1802 places the chip into a kind of stasis with an amazingly low power consumption... on the order of several NANO-WATTS in some parts.

A process for screening production chips to identify these special parts was developed but RCA declined to implement it. This screening was conducted regularly, here from standard production runs of 1802s and these special chips were used in implantable medical devices until fairly recently. I don't yet know the specifics on these devices, I presume them to be pace makers and timed medication delivery devices and I don't know the quantities but presume them to be experimental and in the hundreds.

While the 1802 was special for me (it set me on a rewarding career path), it should be special in the hearts of, perhaps, hundreds of folks who have benefited from having it pumping away inside them to regulate their own heartbeat and deliver medication. It should be special to thousands of scientists around the world whose research would not be possible without it. It should be special to tens of thousands of Amateur Radio operators who rely on it for the operations of the satellites they frequently communicate through. And it should be special to the millions of people who have marveled at the images of other worlds brought to them courtesy of the quirky little 1802.

I really hate to see it relegated to what some have called "an odd, archaic, primitive micro controller" but if primitive it is... well, it works well enough to be in some of the most prestigious places in the solar system... and beyond!

Steve Gemeny

References with notes by Herb Johnson 2011

1) AO-40 (P3D) IMU-2 an experimental replacement for the 1802
A0-40 (P#D) IMU
Note: the above are dead links in 2011, Wikipedia describes the AO-40 AMSAT

2) Galileo FAQ
Galileo Engineering information
Note: the above are dead links in 2011, here's NASA's Galileo legacy site

3) Galileo Current Events
Note: the Galileo program has no current events in 2011, see the above.

Contact information:
Herb Johnson
New Jersey, USA
To email @ me, see
see my home Web page.

This page and edited content is copyright Herb Johnson (c) 2019. Copyright of other contents beyond brief quotes, is held by the authors of those contents. Contact Herb at www.retrotechnology.com, an email address is available on that page..