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data table is still valid and could be used in the repair of any equipment still fielded, but the interface as a whole is obsolete.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.
| 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 | |
| 33 | TERMPWRB | 34 | TERMPWRB |
| 35 | TERMPWRB | 36 | TERMPWRB |
| 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.
Navigation > Engineering Home > Interface Buses > Cable Buses > SCSI Bus > SCSI 'B' Cable.
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