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Some earlier PS/2s (including some or all Model 50s, 60s, 70s and 80s) used
diskette drives with 40 way card edge connectors. These fitted into a frame
which contained the female connector. Later machines used a 34 way 2 row header
instead.
There is an adapter cable that connects the 40 pin
card edge connector to the newer 34 pin header connector. It is used
(for example) when installing the Internal Tape Backup Unit (ITBU) or
the External Diskette Drive adapter (the dummy drive cage) to machines that
do not use the edge connector interface. It might also be useful in extremis if it
were necessary to fit an older drive to one of the newer Model 80s (the actual
drive retention cage is the same).
The IBM version of this cable uses about 3cm of 34 way ribbon cable,
with the (female) edge connector on one end and a (male) header connector on the
other. However, wiring is not 'straight through'; the power
connections differ between the two interfaces.
Diskette Drive 34-Pin to ITBU 40-Pin Connector (Adapter Cable 34F2717)
Included in Internal Tape Backup Unit Installation Kit B
This is from the EPRM
(agrees with the table in 64F7470 / G571-0204-00):
34 Pin
(to planar)
Pin No. |
Signal Name |
40 Pin
(to ITBU)
Pin No. |
| 1 |
2nd Drive installed |
1 |
| 2 |
-High Density Select |
2 |
| 3 |
+ 5 Vdc |
38 |
| 4 |
Ground |
4 |
| 5 |
Ground |
5 |
| 6 |
+ 12 Vdc |
40 |
| 7 |
Signal Ground |
7 |
| 8 |
-Index |
8 |
| 9 |
(No Connection) |
9 |
| 10 |
-Motor Enable 0 |
10 |
| 11 |
Signal Ground |
11 |
| 12 |
-Drive Select 1 |
12 |
| 13 |
Ground |
13 |
| 14 |
-Drive Select 0 |
14 |
| 15 |
Signal Ground |
15 |
| 16 |
-Motor Enable 1 |
16 |
| 17 |
(No Connection) |
17 |
| 18 |
-Direction |
18 |
| 19 |
Signal Ground |
19 |
| 20 |
-Step |
20 |
| 21 |
Signal Ground |
21 |
| 22 |
-Write Data |
22 |
| 23 |
Signal Ground |
23 |
| 24 |
-Write Enable |
24 |
| 25 |
Signal Ground |
25 |
| 26 |
-Busy |
26 |
| 27 |
(No Connection) |
27 |
| 28 |
-Write Protect |
28 |
| 29 |
Signal Ground |
29 |
| 30 |
-Read Data |
30 |
| 31 |
Signal Ground |
31 |
| 32 |
-Head 1 Select |
32 |
| 33 |
(No Connection) |
33 |
| 34 |
-Ready |
34 |
For completeness, here are all of the connections required:
Note: This goes to a header on a Model 80,
and I would heartily recommend checking the pinout for the 40 or 44 pin header
used on the later systems BEFORE you wire this up...
| Edge connector pin |
Header connector pin |
Signal |
| 1 |
1 |
Ground |
| 2 |
2 |
-High Density Select |
| 3 |
No connection |
Reserved |
| 4 |
4 |
Drive Type ID 1 |
| 5 |
5 |
Ground |
| 6 |
No connection |
Reserved |
| 7 |
7 |
Ground |
| 8 |
8 |
-Index |
| 9 |
9 |
Ground |
| 10 |
10 |
Reserved |
| 11 |
11 |
Ground |
| 12 |
12 |
-Drive Select |
| 13 |
13 |
Ground |
| 14 |
14 |
Reserved |
| 15 |
15 |
Ground |
| 16 |
16 |
-Motor Enable |
| 17 |
17 |
Ground |
| 18 |
18 |
-Direction In |
| 19 |
19 |
Ground |
| 20 |
20 |
-Step |
| 21 |
21 |
Ground |
| 22 |
22 |
-Write Data |
| 23 |
23 |
Ground |
| 24 |
24 |
-Write Enable |
| 25 |
25 |
Ground |
| 26 |
26 |
-Track 0 |
| 27 |
27 |
Ground |
| 28 |
28 |
-Write Protect |
| 29 |
29 |
Ground |
| 30 |
30 |
-Read Data |
| 31 |
31 |
Ground |
| 32 |
32 |
-Head 1 Select |
| 33 |
33 |
Ground |
| 34 |
34 |
-Diskette Change |
| 35 |
No connection |
Ground |
| 36 |
No connection |
Ground |
| 37 |
No connection |
Ground |
| 38 |
3 |
+5V DC |
| 39 |
No connection |
Ground |
| 40 |
6 |
+12V DC |
In practice, manufacture of this cable is fairly straightforward.
Cut a short piece of 34 way ribbon cable (about 6cm). Fit the 34 way
header connector in the normal way, remembering that the edge with the
red stripe goes to pin 1. Separate out wires 3 and 6 for most of the
length of the cable, leaving about 1cm intact nearest the header
connector. Cut the three main parts of the cable (wires 1-2, 4-5, and 7-34)
back to about 3cm in length. Trail wires 3 and 6 across the surface of
the rest, and hold temporarily in place with a small piece of sticky
tape. Fit the edge connector loosely, making sure that the wires all go
in the right connectors (a gap of one wire between each of the first three
sections, counting from pin 1, a 3 wire gap to the single wire from pin 3
on the header, and a 1 wire gap between that and the final wire
(from pin 6 on the header). When all is in place, crimp it all home.
It may be worth winding some wide tape round the cable, transversely, to avoid
the two single wires snagging on something when the cable is fitted.
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