Here is a netlist of connections and a parts listing for building the APE Pro System cable that allows you to connect your PC to the Atari
                                                SIO bus. 

                                             Materials Required 

                                    Any general purpose PCB. (Radio Shack)
                              1/2 of Cut SIO Cable (American Technavision, B&C, Etc)

                                      IBM Serial Connector (Radio Shack)
                                            (DB9 Pinouts given)

 5+ conductor wire. (Radio shack, but you might want to consider just re-using some dead cable you have laying around. Like a joystick
                                          cable w/ both ends cut off)
                                         ~1.2k Resistor (Radio Shack)

                            4 x 22uf 25v caps, (Radio shack, or Digikey part # P6236-ND)
                                    electrolytic. (Digikey cost ~ 8 cents each)

                   ICL232 Cmos<-->TTL RS232 converter (Digikey part # ICL232CPE-ND ~ $3 each)

                                               Connections
                                                ----------- 

                                         Pc Ground -> ICL232 Pin 15
                                          Pc DTR -> ICL232 Pin 8
                                          Pc TxD -> ICL232 Pin 13
                                          Pc RxD -> ICL232 Pin 14

                             +5v Source -> ICL232 Pin 16 (9v battery works OK for me)
                                       Source Ground -> ICL232 Pin 15 

                                     Atari Ready (LtBlue) -> ICL232 Pin 16
                                    Atari DataOut (Green) -> ICL232 Pin 12
                                    Atari Command (Purple) -> ICL232 Pin 9
                                    Atari DataIn (Orange) -> ICL232 Pin 11
                                     Atari Ground (Black) -> ICL232 Pin 15 

                                 1.2K Resistor - ICL232 Pin 16 -> ICL232 Pin 11 

                                          Cap #1 - (+) ICL232 Pin 1
                                             (-) ICL232 Pin 3 

                                          Cap #2 - (+) ICL232 Pin 4
                                             (-) ICL232 Pin 5 

                                         Cap #3 - (+) ICL232 Pin 15
                                             (-) ICL232 Pin 6 

                                          Cap #4 - (+) ICL232 Pin 2
                                             (-) ICL232 Pin 16