LF: Re: Fterm with Modem


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LF: Re: Fterm with Modem



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> From: MR MATTHEW R DALSANTO <JNWB99B@prodigy.com>
> To: list-fargo@LISTS.TICALC.ORG
> Subject: LF: Fterm with Modem
> Date: Sunday, November 17, 1996 3:14 PM
> 
>       I have hooked up my TI-Graph Link 25 pin head to a 25 pin to 25 
> pin Interex thing and then to the back of my modem.  When I input the 
> initialization string in Fterm nothing happens.  The modems light are 
> on and I know it works.  It is a Zoom 14.4 Ex.  I have heard about 
> the null modem things, but what are they?
> 
> 
>                        Thanks for any help,
>                        Matt 
Look at this:


RX=Receive Line
TX=Transmit Line


Computer TX  ---> Calc RX
Computer RX <--- Calc TX


Computer TX   ---> Modem RX
Computer RX  <--- Modem TX


without Null Modem Adapter


Modem TX   ---> Calc TX
Modem RX  <--- Calc RX


with Null Modem Adapter


Modem TX   ---> Calc RX
Modem RX  <--- Calc TX






You need a null modem adapter.  I believe they swap the TX and receive
lines so that an ordinary serial cable can be used to communicate between
computers. If you look at the 3 scenarios above, usually the first two
occur normally. Since the calculator and modem are both made to communicate
to the computer, their TX and RX pins are certain ones. The computer has
these reversed to it can "talk" and "listen".   WHen you hooked the
calculator to the modem, the RX and TX lines were on the coresponding RX
and TX lines on the modem.  The result: the two devices are trying to talk
on the same line as the other talks on and listen on the same line the
other listens on.  A null modem adapter reverses these two lines to that
they are correctly connected.




Let me know if it helps!


References: