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ST-412 and ST-506

ST-412 Interface (MFM and RLL).
ST-506 was predecessor without buffered seek.
2 Cables: 34-pin Command Cable and 20-pin Data Cable.

Note: The 34-pin cable was connected to all the drives, but each (of upto four) drives had it's own 20-pin cable, I am quite sure, Jaap.

J1 (34-pin Command) Host/Drive Pin Assignments

Ground return pin Signal pin Signal
1 2 -Head select 2**3
3 4 -Head select 2**2
5 6 -Write gate
7 8* -Seek complete
9 10* -Track 0
11 12* -Write fault
13 14 -Head select 2**0
15 16 -Reserved
17 18 -Head select 2**1
19 20* -Index
21 22* -Ready
23 24 -Step
25 (29)** 26 (28) -Drive select 1 (2)
27 (27) 28 (26) -Drive select 2 (1)
29 (25) 30 -Drive select 3
31 32 -Drive select 4
33 34 -Direction in

Notes:
* Status enabled with drive select
** Twisted cable in parentheses

J2 (20-pin Data) Host/drive pin assignments

Ground return pin Signal pin Signal name
2 1 -Drive selected
4 3 Reserved
6 5 Reserved
8 7 Reserved
10 9 Reserved
12 11 Ground
13 +MFM (RLL) WRITE DATA
14 -MFM (RLL) Write data
16 15 Ground
17 +MFM (RLL) Read data
18 -MFM (RLL) Read data
20 19 Ground
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