Lear Siegler, Inc. (LSI) Terminal ADM-3A

LSI ADM-3A, front view The LSI ADM-3A is a unique piece of hardware. I think it's the only terminal with a bakelite casing ever made. It was built by the Lear Siegler, Inc located in Anaheim, California. The first units were shipped in mid 1974 (that's even before the famous DEC vt100 was made)!

Back then the ADM-3A was a very popular terminal. The first version of the editor vi was written by Bill Joy using an ADM-3A. Surprise.. there are arrows printed on the keys h,j,k,l! And could this this be the reason why the home directory shortcut is ~ with Unix? The ADM-3A is also the reason for the existance of the word terminak. According to Brian M. O'Connell's page it was available as a kit ($995) or assembled ($1195).

Quoting Dennis Cagan, who had joined LSI as the regional sales manager in 1973:

All its functions are implemented using TTLs, except for three special puropose ICs.

One of the more remarkable "features" is that it only can display upper case letters.. there is some add-on chipset which enables lower case letters. There are even terminals out there emulating the ADM-3A, such as the ADDS 4000/110 .

It looks like one of those old 1960s TV-sets.. somehow it always reminds me of the movie "Brazil"... :)
The ADM-3A was built very solid, Rich Kulawiec reports on a news group dedicated to the LSI ADM-3A ( alt.religion.adm3a .. read this quote from the Yucks Digest on the creation of this newsgroup) that his ADM-3A even survived being bounced down a flight of stairs. With its weight of around 14 kg I would not prefer having a ADM-3A tossed onto me...

One of the reasons why it is that heavy is that it is not using a switched power supply but a simple mains transformer..

LSI ADM-3A, inside The casing consists of two halves, the bottom one and the top one which looks like a half egg and can be swung open to the back. The bottom contains the keyboard, a circuit board containing mainly TTLs and below that the transformer. The top of the casing contains the CRT and the necessary electronics to drive the CRT.

The keyboard is also very interersting. You can pull off the keys, but don't expect the usual, encapsulated microswitches. The keys are stuck onto hollow plastic squares which contain the alligator-clip like copper contacts. When the keys are pulled off you can see the contacts and watch them close as the plastic squares are pushed down. And it got arrows printed onto the keys h, j, k and l - what do you need more.

At the back there are two serial connectors, one labeled "modem" (this is where we plug in the terminalserver) and one labeled "extension".

As everything is implemented in hardware, there's also no setup menu or anything comparable. The setup is done using DIP-switches which are located at the left of the keyboard, hidden under a panel which is screwed to the casing.

Following are the DIP-switches as labeled on the terminal and their meanings:

Description DIP Position 1 DIP Position 2Explanation
BIT 801this term only does 7bit. set unused 8th bit to 1 or to 0?
PARITY-INHenable or inhibit the parity bit?
STOP121 or 2 stop-bits? (nowadays, default is 1)
DATA78use 7 or 8 data bits?
PARODDEVENodd or even parity?
LCENUCuse lower case and upper case as created using shift or always do uppercase?
.AUTO NLOFFautomatically do a newline when the right end of the screen is reached?
.RS232CLSelect RS232 or 20mA Current Loop connection
.HDXFDXhalfduplex or fullduplex? (Terminal does a local echo in HDX mode)

Then follows a row of DIP switches of which only one may be set, setting Baud rates of 19200, 9600, 4800, 2400, 1800, 1200, 600, 300, 150, 110 or 75 Baud.

The picture tube is a Samsung 12ZBY31N (green), and has some very interesing stickers attached to it.
One says "Do not use ion trap" (click here for an explanation what this means), another one reads:

Very interesting indeed, given the fact that the stickers on all CRTs today state that "this picture tube is shielded against X-Ray radiation" and "max. 25kV" or similar...

Yet another sticker right below the serial connectors at the back of the terminal reads:

I guess my neighbors won't be very pleased.. :)

ADM-3A, operating

The company LSI itself has been closed down and auctioned off quite some time ago.

Links to other adm3a resources

  • ADM-3A User Manual and Maintenance Manuals as PDFs - very useful stuff!
  • ADM-3A Operator's Manual as PDF
  • ADM-3A Maintenance Manual as PDF
  • Homebrew lower-case option by Steve Loboyko
  • Lear-Siegler Terminal at old-computers.com, with a comment from one of the co-inventors of the ADM-3A
  • ADM-3A Page of the University of Erlangen
  • Dumb Terminal Kit Announcement from Elementary Electronics magazine
  • Bryan's ADM-3A page
  • Brian M. O'Connell's page on old computer hardware
  • adm3a page from the collection of the The University of Stuttgart (German language)

    Page last modified: Sun Nov 29 15:47:50 CET 2015

    Change history:
    2015-11-29: After 14 years of no updates to this page I finally got round to do it:
  • proper rescan of the original 35mm negatives back from 2000.. the images are of much better quality now
  • included input from Dennis Cagan, who contacted me via email. Fixed some errors he pointed out.
  • the proper spelling is ADM-3A, not ADM3A. corrected it.
  • fixed four broken links. Broken links, imagine that! After not even 15 years!