Apple's SCSI cables are built to tight specifications to minimize electrical noise on the SCSI bus. The wires are laid out to provide minimal signal degradation. Poor quality cable construction may lead to intermittent SCSI operation and potential system crashes.
HDI-30 plug pin layout
(found on SCSI Disk Adapter Cable M2539LL/A)
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30 29 28 27 26 25
24 23 22 21 20 19
18 17 16 15 14 13
12 11 10 9 8 7
6 5 4 3 2 1
BR-50 connector pin layout (found on SCSI Disk Adapter Cable M2539LL/A)
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25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26
HDI-30 BR-50 Name Signal Description
------ ----- ---- ------------------
2 26 /DB0 SCSI data bit 0
1,3 19 GND Ground, Pin 1 enables SCSI disk mode
4 27 /DB1 SCSI data bit 1
5 38 TERMPWR Termination power (not supplied by PowerBook 100)
6 28 /DB2 SCSI data bit 2
7 29 /DB3 SCSI data bit 3
8 1,4 GND Ground
9 44 /ACK SCSI acknowledge
10 5 GND Ground
11 30 /DB4 SCSI data bit 4
12 2,3,8 GND Ground
13 11,9,6 GND Ground
14 31 /DB5 SCSI data bit 5
15 24 GND Ground
16 32 /DB6 SCSI data bit 6
17 7 GND Ground
18 33 /DB7 SCSI data bit 7
19 34 /DBP SCSI data bit parity
20 23,16,20 GND Ground
21 49 /REQ SCSI request
22 21,22 GND Ground
23 43 /BSY SCSI busy
24 25 GND Ground
25 41 /ATN SCSI attention
26 48 /C/D SCSI control/data
27 45 /RST SCSI bus reset
28 46 /MSG SCSI message
29 47 /SEL SCSI select
30 50 /I/O SCSI input/output