**<>**¢ 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**¢¢
