**<>**› RS232 Modem and Null Modem cables for› the 850 Interface Module, by › HENRY HAHLBOHM for OL' HACKERS A.U.G.›› --------------------------------------›     This  is  a description  of serial› cables to be used  with   Atari  8-bit› 850 compatible RS232 interfaces. ››     Port  1  of  the   850   interface› module    has    the   following   pin› assignments:›› Pin             Function › ---             --------› 1    Data Terminal Ready (DTR) output.› 2    Carrier Detect (DCD) input. › 3    Transmit data (Xmit) output.› 4    Receive data (Rec) input.› 5    Signal ground (GND).› 6    Data Set Ready (DSR) input.› 7    Request to Send (RTS) output.› 8    Clear to Send (CTS) input.› 9    no connection. ››       To connect the Atari 850 port  1› to  a  modem  requires a cable with  a› male DB9 connector at  the  Atari  end› and  a  male  DB25  connector  at the › modem end. The wiring is as follows:›› Atari end                  Modem end› ---------                  ---------› 1...............DTR...............20› 2...............DCD................8› 3...............Xmit...............2› 4...............Rec................3› 5...............GND................7› 6...............DSR................6› 7...............RTS................4› 8...............CTS................5›› WHATS NEEDED:››        To   connect   the   Atari  850› directly to a PC without going through› a  modem   requires   a   null   modem› connection.   If  you  have  the above› Atari modem cable and  a  modem  cable› for your PC the easiest thing to do is› to   buy  a  Radio  Shack  Null  Modem› adapter and  simply  connect  the  two› cables together with the adapter.  You› may need a Gender Changer  adapter  in› order  to  make the connection because› the Null Modem adapter normally  comes› with a male and a female end while two› female ends are required.›› MAKING YOUR OWN››        If you want to  make  your  own› null  modem  cable  you will require a› DB9 male connector for the Atari end. › The  PC  end is normally a female DB25› or a female DB9 connector.  If the  PC› has  a  25 pin connector the wiring is› as follows:›› Atari end                    PC end› ---------                   -------› 1....DTR...................DSR....6› 2.   DCD                   DCD  |.8› 6.|..DSR...................DTR...20› 3....Xmit..................Rec....3› 4....Rec...................Xmit...2› 5....GND...................GND....7› 7....RTS...................CTS....5› 8....CTS...................RTS....4›› Note: Pins 6&8 jumpered at PC end›       Pins 2&6 jumpered at Atari end››› WHAT IF?››      If  the  PC has a 9 pin connector› the wiring is as follows:›› Atari end                     PC end› ---------                    -------› 1....DTR....................DSR....6› 2.   DCD                    DCD  |.1› 6.|..DSR....................DTR....4› 3....Xmit...................REC....2› 4....Rec...................Xmit....3› 5....GND....................GND....5› 7....RTS....................CTS....8› 8....CTS....................RTS....7›› Note: Pins 1&6 jumpered at PC end›       Pins 2&6 jumpered at Atari end››› DO YOU NEED ALL THESE H/S LINES?››     Depending  on  your  software, you› may not need all the handshake lines. › You  may  be  able to get away with as› few as three wires (GND,  Xmit-Rec,and› Rec-Xmit).   However,   if   your   PC› software  makes  any  DOS calls to the› comm  port,  you  will  need  all  the› handshake lines.››                **end**››