[Xastir] I finally got it!

[Curt, WE7U]

On Fri, 17 Sep 2010, Michael Lewis wrote:

> Yep I found that same site
>
> the null modem I got from ebay months ago no clue what type pf null modem 
> cable it is.. I just know when connected to the splitter and with it's null 
> modem  I can't connect to the tracker at all.. I have no other serial cables 
> here so I had to buy a 6Ft cable off ebay last night for around $2.49 free 
> ship.

Do you have a meter?  Analog or DMM?  If so, you can check between
pins 5 (GND) and 2 on a DE-9 (contrary to public opinion, it's a DE
and not a DB for a 9-pin).  Then do the same for pins 5 and 3.  2
and 3 are your TXD/RXD pins, which are the ones your data goes down
in each direction.  If pin2 on one connector is being driven (+3 to
+12VDC or -3 to -12VDC) then you don't want to connect it to another
connector that also has pin 2 driven.  In that case you'll need a
null-modem cable or adapter to connect the two.

If pin 2 is driven on one, and pin 3 is driven on the other, then
you can connect the two.

It can be a LOT more complicated than that with all the possible
cable wirings out there, but those two pins are the main ones to
worry about.  For DB-25 cables (yes, DB now instead of DE), it's
pins 2/3 and pin 7 for ground.

What you might want to do if you play around with RS-232 quite a bit
is get some null-modem adapters and an RS-232 LED breakout box.
Using the breakout box you can plug it into one cable and see one
LED light up, plug it into the other and see a different LED light
up, and know that you can connect the two cables.  This is the type
of thing I'm talking about:

     http://www.scancat.com/minitstr.html

Radio Shack used to sell the adapters and the LED breakout box.  I
have several plus various 9-25, m-m, f-f, and laplink type cables so
I can pretty much adapt to anything at a moment's notice.

-- 
Curt, WE7U.                         <http://www.eskimo.com/~archer>
    APRS:  Where it's at!                    <http://www.xastir.org>
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