Single-Ended Data Pinout
The "A" cable is used with 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 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' Single-ended data cable is listed
below. The differential pinout for the A Cable is shown on the Differential A Cable
page.
The A cable has 50 conductors and provides an 8 bit data bus. The interface is Single-ended (unbalanced) with a cable length at 6 meters. SCSI-I used a Centronics 50 pin connector, 0.10 inch spacing, with 0.05 inch ribbon cable. While SCSI-II provided 8 bit data over a Micro D 50 pin, high density (50 mil). The 'A' cable impedance is between 90 and 140 ohms. The minimum conductor size is 28 AWG solid or stranded. For Connector and Cable Assembly manufacturers refer to the main SCSI page. With the advent of SCSI-4 in 2002, and then SCSI-5 in 2003, the 'A' cable is obsolete and should not be used for new designs. Also refer to the main Connector manufacturers page, Cable manufacturers page, and Cable Assembly manufacturers
| Pin # | Pin Function | Pin # | Pin Function |
| 1 | Ground | 26 | D0- |
| 2 | Ground | 27 | D1- |
| 3 | Ground | 28 | D2- |
| 4 | Ground | 29 | D3- |
| 5 | Ground | 30 | D4- |
| 6 | Ground | 31 | D5- |
| 7 | Ground | 32 | D6- |
| 8 | Ground | 33 | D7- |
| 9 | Ground | 34 | DPARTY- |
| 10 | Ground | 35 | Ground |
| 11 | Ground | 36 | Ground |
| 12 | Reserved | 37 | Reserved |
| 13 | Open | 38 | TRMPWR |
| 14 | Reserved | 39 | Reserved |
| 15 | Ground | 40 | Ground |
| 16 | Ground | 41 | ATN- |
| 17 | Ground | 42 | Ground |
| 18 | Ground | 43 | BSY- |
| 19 | Ground | 44 | ACK- |
| 20 | Ground | 45 | RST- |
| 21 | Ground | 46 | MSG- |
| 22 | Ground | 47 | SEL- |
| 23 | Ground | 48 | C/D- |
| 24 | Ground | 49 | REG- |
| 25 | Ground | 50 | I/O- |
The "B" Single-Ended cable pinout is listed on the SCSI Bus 'B' connector page.
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 pin out 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.
Design Key words: SCSI Physical Interface, Bus, Small Computer Systems Interface, SCSI Pin outs, SCSI PinOut, Pin Out, Signal/Differential Pin-outs, Pin Outs, A Connector, Signal Names, row, Pin Descriptions, Peripheral Computer Hard Drive Data Bus, Parallel data bus, Description, SCSI-1, SCSI-2, SCSI-3, Parallel SCSI, Direct Attached Storage [DAS], Networked Attached Storage [NAS], Storage Area Network [SAN]
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