The original floppy cable required that each drive was jumpered to the right ID. But IBM come up with an idea to avoid jumpering the floppies.
If wire 10-16 are twisted before the last connector the jumpering is avoided. Each drive should be jumpered to act as Drive 2. If only one drive is used then leave the middle connector free.
The IDC could also be an edge connector on some old drives.
Controller Drive 2 Twist Drive 1 +--+ +--+ +--+ |::|===================| |============| | <-Pin 1 |::|===================| |=====/=====| | |::|===================| |=====/=====| | |::|===================| |============| | |::|===================| |============| | |::|===================| |============| | |::|===================| |============| | +--+ +--+ +--+
| Controller | Drive 1 | Drive 2 | |
|---|---|---|---|
| Wire 1-9 | 1-9 | 1-9 | 1-9 |
| Wire 10 | 10 | 16 | 10 |
| Wire 11 | 11 | 15 | 11 |
| Wire 12 | 12 | 14 | 12 |
| Wire 13 | 13 | 13 | 13 |
| Wire 14 | 14 | 12 | 14 |
| Wire 15 | 15 | 11 | 15 |
| Wire 16 | 16 | 10 | 16 |
| Wire 17-34 | 17-34 | 17-34 | 17-34 |
correct
incorrect