IBM PS/2 Mod. 55SX
                   Diskette Drive Controller Pinout

+-----+-----+----------------------+-----+-----+----------------------+
| Pin | I/O |  Signal Description  | Pin | I/O |  Signal Description  |
+-----+-----+----------------------+-----+-----+----------------------+
|  1  |  -  |  Reserved            |  2  |  O  |  -High Density Sel.  |
|  3  |  O  |  +5V DC              |  4  |  -  |  Reserved            |
|  5  |  -  |  Ground              |  6  |  O  |  +12V DC             |
|  7  |  -  |  Ground              |  8  |  I  |  -Index              |
|  9  |  -  |  Ground              | 10  |  -  |  Reserved            |
| 11  |  -  |  Ground              | 12  |  O  |  -Drive Select       |
| 13  |  -  |  Ground              | 14  |  -  |  Reserved            |
| 15  |  -  |  Ground              | 16  |  O  |  -Motor Enable       |
| 17  |  -  |  Ground              | 18  |  O  |  -Direction          |
| 19  |  -  |  Ground              | 20  |  O  |  -Step               |
| 21  |  -  |  Ground              | 22  |  O  |  -Write Data         |
| 23  |  -  |  Ground              | 24  |  O  |  -Write Enable       |
| 25  |  -  |  Ground              | 26  |  I  |  -Track 00           |
| 27  |  -  |  Ground              | 28  |  I  |  -Write Protect      |
| 29  |  -  |  Ground              | 30  |  I  |  -Read Data          |
| 31  |  -  |  Ground              | 32  |  O  |  -Head 1 Select      |
| 33  |  -  |  Ground              | 34  |  I  |  -Disk Change        |
| 35  |  -  |  Ground              | 36  |  -  |  Ground              |
| 37  |  -  |  Reserved            | 38  |  O  |  +5V DC              |
| 39  |  -  |  Ground              | 40  |  O  |  +12V DC             |
+-----+-----+----------------------+-----+-----+----------------------+

The 55SX uses the Type 1 diskette drive controller but with a
different pin-out than shown in the "IBM PS/2 Hardware Interface 
Technical Reference".