Subject: DB-25 Connector hookup


   I was at a Ham fest last Suanday and overheard two hams talking about
hooking up a RS-232 cable. Both thought all 25 pins MUST be used when
making up such a cable for their shack use.

   Well, it may look like you must use all 25 pins, after all, why was the
DB-25 connector developed in the first place and now the standard for all
hookups ?  The fact is, you'll find that in most cases or hookups, all
25 pins on a DB-25 connector are never used.

  Here are the most used pin outs used when making up your own RS-232
cable to a DB-25 male or female connector.

  First I'll list the most used pin-outs and their signals and what they
mean.

  Signal        Function                                   Pin#
------------------------------------------------------------------------
  PGND          Protective Ground                           1
  TD            Transmit Data                               2
  RD            Receive Data                                3
  RTS           Request to Send                             4
  CTS           Clear to Send                               5
  DSR           Data Set Ready                              6
  SGND          Signal Ground                               7
  CD            Carrier Detect                              8
  DTR           Data Terminal Ready                        20

----------------------------------------------------------------------------

   Those lines listed above are the only lines you're ever going to use in
most cases with any of your gear in your shack, including your TNC to CPU.

   Now with the above info known, here are some pin to pin hookups from
one DB-25 to another DB-25.

   This pin out is called the RS-232 minimum cable.


                    PIN                    PIN
                     1 -------------------  1
 Connector 1         2 -------------------  2    Connector 2
                     3 -------------------  3
                     7 -------------------  7

  This next one is called the RS-232 full cable.

                    PIN                    PIN
                     1  ------------------  1
  Connector 1        2  ------------------  2     Connector 2
                     3  ------------------  3
                     4  ------------------  4
                     5  ------------------  5
                     6  ------------------  6
                     7  ------------------  7
                    20  ------------------  20

   Ever hear of a RS-232 Null Modem cable ? If you ever need one, just make
your own one up like this.

                     PIN                      PIN
                     20  --------------------  6
 Connector 1          6  --------------------  20     Connector 2
             Jumper 4&5  --------------------  8
                      8  --------------------  4&5 Jumper
                      2  --------------------  3
                      3  --------------------  2
                      7  --------------------  7

  One thing to always keep in mind. You'll never BLOW anything if you make
a mistake. Also some CPU's hooked to TNC's won't work just right or lock
up once in a while. Try this if your terminal program acks up or locks up.
On the CPU end of your DB-25 connector, jumper pins 6, 8 and 20 together.

  Hope the above helps and saves you money. Why give a computer store big
buxs when you can do it yourself and save!

   73 de Bill N8FIS @ N8FIS -:- Fremont, OH. -:-