This file contains the pin-outs to go from the 9-pin asynch port of an AT to a standard 25-pin RS-232 adaptor. Recently I needed to hook my PC to a main-frame and discovered that the 9-pin standard for the PC-AT asynch port was an unknown quantity in the main-frame world, so I needed to make an adaptor. Since an asynch port is an asynch port regardless of the number of pins it has, all I had to do was find the correspondence between the 9-pins and the 25-pins. It took a LOT more digging to find what I was looking for, so I decided to post this where others could get to it without the trouble I had to go to. If you have an AT, and an external modem with a standard RS-232 25-pin connector, and no adaptor, then this is how you can build you're own cable. Note that the connectors (9-pin female, 25-pin male), hoods, and wires, should run you about $5. To buy the cable ready made from friendly BIG BLUE would run you (retail) > $35! Let's here it for market competition! ---------------------------------------- Pin numbering schematic: Note: All of the below pinouts are to be interpreted as if you were looking at them from the perspective of a connector about to be plugged into them; e.g. you're looking into them, not out from them. RS-232 male: x( 1) x( 2) x( 3) x( 4) x( 5) x( 6) x( 7) x( 8) x( 9) x(10) x(11) x(12) x(13) x(14) x(15) x(16) x(17) x(18) x(19) x(20) x(21) x(22) x(23) x(24) x(25) 9-pin asynch. male: x( 1) x( 2) x( 3) x( 4) x( 5) x( 6) x( 7) x( 8) x( 9) RS-232 female: o(13) o(12) o(11) o(10) o( 9) o( 8) o( 7) o( 6) o( 5) o( 4) o( 3) o( 2) o( 1) o(25) o(24) o(23) o(22) o(21) o(20) o(19) o(18) o(17) o(16) o(15) o(14) 9-pin asynch. female: o( 5) o( 4) o( 3) o( 2) o( 1) o( 9) o( 8) o( 7) o( 6) ---------- pin conversions: 25 pin RS-232 <--> 9 pin asynch. pin # pin # 1 connector case (ground) 2 . . . . . . . . 3 3 . . . . . . . . 2 4 . . . . . . . . 7 5 . . . . . . . . 8 6 . . . . . . . . 6 7 . . . . . . . . 5 8 . . . . . . . . 1 20 . . . . . . . . 4 22 . . . . . . . . 9 Good Luck!