Secrets of the Coleco ADAMLink Modem

Are there secrets today hidden from even the owners of the Coleco ADAMLink modem?  Yes, but they are accidental secrets, simply lost to the passage of time alongside our assumptions about modern technology.  I recently re-acquired one of these modems to further the development of my 1986 ADAMCastle BBS re-release for Christmas 2021.

The ADAMLink modem fits in expansion slot number 1 and delivers 300 baud (bits per second) transmission speed.  Roughly speaking, this would be up to one line of ADAM screen text per second under ideal connection conditions.  Whether you have only heard of this relatively rare modem, owned one long ago, or are super-lucky to have one installed today, chances are I’m going to reveal AT LEAST ONE thing you probably didn’t know about it, or have maybe forgotten.  I’ll start with the easy secrets and then move on to the harder ones so you can keep score.

Is the phone line connection the first secret?  Apparently yes, if you don’t have the manual.  While there are some cool Coleco ADAM reviews on YouTube, I found more than one video or public comment which claimed the jack on the left side of the ADAM memory console is where the modem connects to your home phone line.  PLEASE DON’T.  Actually that is a 62,500 baud ADAMNet jack for external peripherals such as disk drives or the keyboard.  Trust me, poor ADAM might have a serious and lasting breakdown if you make this easily mistaken modem connection!  The ADAMNet jack is only designed for a 5-volt signal, but a landline telephone ring signal generates a 20 hertz sine wave between 60 and 105 volts!  I think you can see the problem too.

Surely the confusion must come from the case labeling “ADAMNet”, leading some today to think of the Internet or a network.  Had ADAM been born 10 years later in 1993 this might have become the obvious connection design!  Instead, the ADAMLink modem requires a special Coleco modem cable which plugs through the vent holes on the TOP expansion door and then into the TOP of the modem itself.  This unique cable has an L-shaped connector on one end and a standard RJ11 wall plug on the other.  If you have this modem but not the unique cable, I would recommend trying to find one before they end up discarded with all the other very ordinary landline phone cables going extinct.

Next up, the ADAMLink modem only has pulse dialing.  If you were paying the phone company for optional touch tone service, you could still use the older rotary style pulse dialing method.  Coleco seems to have chosen not to put the touch tone generator parts into the ADAMLink modem to save money.  Maybe pulse dialing still works today but I don’t currently have a landline to do the testing.  I am hoping to verify it later this year.

Our final and biggest ADAMLink secret is the modem is a bit on the deaf side.  If you have ever used the ADAMLink Telecommunicator (terminal) software and wondered where the auto-answer function is, the solution might surprise you.  There IS NO circuitry to “hear” the previously mentioned ring signal!  Therefore our modem could not answer incoming calls unattended.  Talk about a very secure system!  You were expected to press a keyboard button at the exact moment you wanted to make your ADAMLink modem answer.

As a result of this limitation in various modems of the time, early modem enthusiasts shared plans to assemble their own phone line “ring detector” project.  I DID build one of these but I no longer have the device or a copy of those plans.  It could be assembled from a handful of cheap parts found at the local DIY shops such as Radio Shack.  A phone line splitter allowed connections for your modem and the ADAM version of the ring detector.  The detector also plugged into the ADAM game controller port.  When the phone line rang, the detector simulated the pressing of a controller fire button.  Your ADAM BBS or terminal software monitored for this ring/fire signal and knew it was time to connect an incoming caller.  Seriously, if you knew that last one, then congratulations are in order, because YOU ARE AN ADAMLink EXPERT!

As an added BONUS secret (woo-hoo!), some people with electrical skills have inexpensively converted their ADAMLink 300 baud modem into a high speed serial port for use with faster external modems or other serial devices!  These plans are freely available at the ADAM archive ( if you search for the term “modifying”.  The result is “Modifying the Coleco Internal Modem Into a Serial Card.pdf”  It is interesting reading even if you are not feeling up to reworking your modem circuits.  While you are enjoying that site, you might consider a purely optional donation to help keep the site running with more great content.

That sums up what I think are the ”Secrets of the ADAMLink modem.”  Don’t worry though.  As time goes on, we will create new secrets from all the things we have forgotten about our amazing 8-bit ADAM computer.  If you are still needing to read more about ADAM modems, travel back to a Summer of 2012 article for a bit more fun:

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