SCSI B Cable Pinout

The SCSI B cable uses a shielded 68 conductor connector, using 2 rows of 34 male contacts (0.05" spacing). The pin out for the B cable is shown below.
The pinout for the 68-pin connector differs from the cable pinout provided below. The signal-ended B cable has a maximum length of 6 meters.
The cable impedance is between 90 and 140 ohms. The minimum conductor size is 28AWG.
The 68-conductor cable may be either a flat cable or twisted-pair [for Wide-SCSI] cable.
This is one of a series of different cabling solutions for the SCSI interface, all of which are out-dated.
However the data table is still valid and could be used in the repair of any equipment still fielded, but the interface as a whole is obsolete.
The 'B' cabling solution is perhaps one of the older, used with the SCSI I and SCSI II interfaces.

SCSI B Cable PinOut
Pin # Pin Function Pin # Pin Function
1 Ground 2 Ground
3 4 Data bit 8
5 6 Data bit 9
7 8 Data bit 10
9 10 Data bit 11
11 12 Data bit 12
13 14 Data bit 13
15 16 Data bit 14
17 18 Data bit 15
19 20 Parity bit P1
21 22 -ACKB
23 24 Ground
25 26 -REQB
27 28 Data bit 16
29 30 Data bit 17
31 32 Data bit 18
37 Ground 38 Data bit 19
39 40 Data bit 20
41 42 Data bit 21
43 44 Data bit 22
45 46 Data bit 23
47 48 Parity bit P2
49 50 Data bit 24
51 52 Data bit 25
53 54 Data bit 26
55 56 Data bit 27
57 58 Data bit 28
59 60 Data bit 29
61 62 Data bit 30
63 64 Data bit 31
65 66 Parity bit P3
67 68 Ground

Read more on the other SCSI variations;
SCSI-1, SCSI-2, or SCSI-3 to provide "FAST" SCSI with an 8 bit Parallel data bus. Refer here for the main SCSI Bus interface page.
With SCSI-2 the "A" may be used alone or with the "B" cable to provide "WIDE" SCSI allowing a 16 or 32 bit data bus. The pin-out for the 'A' cable is listed on the SCSI Bus 'A' connector pinout page.

The "B" Single-Ended cable pin-out is shown above.
On SCSI-3, the "A" cable may be used for an 8 bit data bus. However the new "P" cable is used to provide a 16 bit data path (wide SCSI). To allow 32 bits of data the "P" cable is combined with another new cable called "Q" (wide SCSI). The "Q" cable pinout is listed on the SCSI Bus 'Q' Single-Ended connector or SCSI Bus 'Q' Differential connector page. The pin-out for the 'P' cable is listed on the SCSI Bus 'P' connector page.

Back to the main SCSI Interface Bus page
The SCSI [parallel] bus width is either 8 bits or 16 bits [Wide bus]. Also the bus may be either Single ended or Differential; however the two are mutually exclusive SCSI is a chained parallel bus, cables start at the Host and run from device to device in a chain. SCSI may be used for asynchronous and synchronous transfers; Asynchronous transfers using Start and Stop bits and synchronous transfers using system timing (Hand-Shaking). The data bus also carries one parity bit.

Editor comment; pages covering topics that are out-dated are noted as being either legacy and/or obsolete.
This particular cable pin out was used with SCSI 2 [circa 1994], which was later replaced by SCSI 3, SCSI 4 and SCSI 5.
The entire line made obsolete with the introduction of Serial SCSI in 2003. However the data is still valid and provided if needed.

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Modified 3/05/12
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