Newsgroups: comp.sys.atari.8bit
Subject: 1489/75LS189 sio2pc design

ATARI=>()       IBM=>[]
SIO CABLE      9 pin serial
          :*             :
(5)------1:in-:          :14------(10)
          :  \ /         :     :
   *NC   2:   o  1   :-in:13 ---
          :   :  4  \ /  :
[2]------3:out   8   o   :12  *NC
          :      9   :   :
(7)------4:in-:       out:11  *NC
          :  \ /         :
   *NC   5:   o      :-in:10------[3]
          :   :     \ /  :
[9]------6:out       o   :9   *NC
          :          :   :
(6)&[5]--7:           out:8--:<--(3)
          :              :  *DIODE
*NOTES: If you're positive the cable will never be used with other
peripherals like a 1050, you don't need the diode. If you do use a
diode  make sure it has a low forward voltage. In the
prototype I tried one with a 1.2V forward drop & it failed to operate,
but a diode with a .65V forward voltage drop worked like gang busters.
This means you can surely get away with any germanium diode & probably
most small signal diodes like the 1N914.
NC means not connected, you don't tie it to anything. Only pins 13 & 14
are tied together.  If you feel bad because the thing is too easy, you
can add a few more parts like a .1 Micro Farad disk capacitor between
pins 14 & 7 for decoupling.  The funny \ /
                                        o  on the 1489 are just an
attempt to show the inverting logic of the 1489. All parts can be had
from your local Radio Shack, but once again, I hate Radio Shack & would
recommend going anywhere else. The SIO pin out when looking at the back
of the Atari is
  2 4 6 8 10 12
 1 3 5 7 9 11 13
Colors I've found in addition to what Nick Kennedy found
4 & 6 Black & or bare wire. Both of these are grounds, one logic & the
other shield. If you really want to be sure you have a good ground you
can use both of them. Black wire is pretty safe if you're in a hurry &
don't want to bother.
10 +5V Blue in every cable I've seen.
5 DATA OUT It's Green or Dark Green on cables with two green wires.
7 COMMAND Violet on some, light green on others.
3 DATA IN & I don't think it comes in any color but orange.
That's it, 5 connections to the Atari serial cable, 4 to the IBM serial
cable, 1 chip, 1 diode. The IBM connector will have the numbers on the
plastic, but you may need a magnifiying glass to see them.  If somebody
wants help building a cable, you're better off asking me about this one
vs the MAX or 7400 as I'm quite bored with them & this circuit is IMO:
The obvious way to go.