original date 3/27/88
Don Wolfe - March 27, 1988 - GEnie Mail Address = D.WOLFE

In my attempt to direct connect my Tandy 1400LT to my Tandy 3000HL I needed
a null modem adapter.  Radio Shack sells only one for the 25 Pin (DB-25)
RS-232C.  Since both the 1400LT and my serial card on my 3000HL have 9 Pin
(DB-9) RS-232C's it would be ludicrous for me to step 9 Pin up to 25 Pin then
interpose a 25 Pin Null Modem Adapter (R.S. No. 276-1496) just to have to
step back down to 9 Pin.  Not to mention the gender mating that would be
necessary.  While my Radio Shack Computer Center assisted me by supplying
a copy of a PCM magazine with an article on 9 Pin to 25 Pin connections (Vol.
V, No. 8, February 1988, "5-to-3 Transfer"), I had to extrapolate from that data the following
pin connections.

Using this information I built a cable that eliminated the need for my
purchasing a Null Modem Adapter and still allowed 9600 b.p.s. direct transfers
using Procomm 2.4.2 in direct connect mode (see Procomm documentation index
under 'Connection Type').  19,200 b.p.s. caused some bad blocks (10 bad when
transferring 41000 bytes), however, I believe this may be eliminated with the
use of shielded cables.


Simple DB-9 To DB-25 Conversion

DB-9    DB-25
 1        8
 2        3
 3        2
 4        20
 5        7
 6        6
 7        4
 8        5
 9        22


DB-25 to Null Modem DB-25

DB-25    NULL DB-25
  8         20,6
  3         2
  2         3
  20        8
  7         7
  6         8
  4         5
  5         4
  22        22


DB-9 To Null Modem DB-9

DB-9    NULL DB-9
  1        4,6
  2        3
  3        2
  4        1
  5        5
  6        1
  7        8
  8        7
  9        9