IBM 7868-047 Modems

Peter Coghlan cctech at
Mon Nov 3 17:07:18 CST 2014

>> If you want to use your modems on the PSTN, the first thing to check is
>> whether they require a single pair connection between them or two
>> pairs.  My ones have RJ11 type connectors which might give the
>> impression that only a single pair is required but two of the pairs are
>> actually used, one for transmit and the other for receive.
>Not quite sure as how I would determine this. One of the questions I have is
>if these modems support Hayes AT commands. In quick testing they do not seem
>to (at least as configured). If they don't then they become pretty much
>useless. If they at least support Hayes commands one could do further
>testing and even set them up to be used locally (in house). I am surprised
>no one has ever run across these guys. I may have to hit up Usenet and the
>modem groups in there for some help

You might have some luck asking on mailing lists etc where IBM mainframe people
hang out.  Donkeys years ago there used to be a list called IBM-MAIN but I
don't know if it still exists or where it is hosted.

>> It is also possible that your modems are synchronous only which will be
>> a problem if you want to talk to asynchronous only modems.
>The only information I have found is at the following link:
>Namely: "There are two and four port models with fan-in/fan-out and/or data
>multiplex functions for both synchronous and asynchronous data terminal
>equipment to share the same link". I am guessing they can work

If they can work asynchronously, it is very likely they only need a single pair
telephone line connection.  It might be worth opening one up and checking how
many conductors are wired to whatever line connector it uses, unless this
is already obvious from the type of connector used.

Peter Coghlan.

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