The ST506/412 interface requires two cables, one for control and one for data. The control cable is shared between the two drives. But each drive has each own data cable. By twisting some wires on the control cable it won’t be necessary to set the ID for each drive, since the twist will do the job. Wires 25 to 29 should be twisted between drive 1 & drive 2.
Controller Drive 2 Twist Drive 1
+--+ +--+ +--+
|::|===================| |============| | <-Pin 1
|::|===================| |============| |
|::|===================| |============| |
|::|===================| |============| |
|::|===================| |=====\/=====| |
|::|===================| |=====/\=====| |
|::|===================| |============| |
+--+ +--+ +--+
Control cable
34 PIN IDC FEMALE to the Controller
34 PIN IDC FEMALE to the Drive 2
34 PIN IDC FEMALE to the Drive 1
| Controller | Drive 1 | Drive 2 | |
|---|---|---|---|
| Wire 1-24 | 1-9 | 1-9 | 1-9 |
| Wire 25 | 25 | 29 | 25 |
| Wire 26 | 26 | 28 | 26 |
| Wire 27 | 27 | 27 | 27 |
| Wire 28 | 28 | 26 | 28 |
| Wire 29 | 29 | 25 | 29 |
| Wire 30-34 | 30-34 | 30-34 | 30-34 |
Data cable
20 PIN IDC FEMALE to the Controller
20 PIN IDC FEMALE to the Drive
| Controller | Drive | |
|---|---|---|
| Wire 1-20 | 1-20 | 1-20 |