NULL modem projects (was Re: Datalinker 1200, etc.)

[rubywand@swbell.net]

Michael Katz-Hyman writes ...
> 
> Can I make a null modem out of a Datalinker 1200 ....
>

??!

     Sure; but, then, you can make a NULL modem out of a bread 
box, too.

     A NULL modem is "no modem". It is typically used for 
directly connecting two terminals or computers via serial I/O.

     A NULL modem is two connectors-- usually, two 25-pin 
female connectors-- wired back-to-back with Send-Receive, etc. 
lines crossed. The idea is that each machine connected to the 
NULL modem 'sees' the other as a modem.

     A typical NULL modem is wired as shown below:

Connector A/ Connector B

 1      -> 1
 2      -> 3
 3      -> 2
 4 & 5  -> 8
 6 & 22 -> 20
 7      -> 7
 8      -> 4 & 5
20      -> 6 & 22
.

     As for building a NULL modem, a Datalinker 1200, 
Micromodem IIe, Patriot 2400, or whatever modem may have the 
advantages of having one of the two connectors needed and a 
nice case.

     You will have to go to the bother of cutting any 
connections from the original connector to the modem circuit. 
You can disconnect the power supply module, as well, since the 
NULL modem needs no power. Naturally, the converted modem will 
be useless as a modem.

     Otherwise, a couple connectors plus a short cable are 
just as good a start; and, the finished product will take less 
table space.


Rubywand