80 pin SCSI SCA-2 female connector
Drive connector: AMP Champ 557613-1 or AMP Champ 557114-5
Cable connector: AMP Champ 2-557103-1 or AMP Champ 2-557101-1
SCA = Single connector Attachment
The SCA-2 (Single Connector Attachment 2) 80-pin connector is a SCSI-3 backplane interface defined to support hot-swap drive installation in server and storage systems. It consolidates all 68 High Voltage Differential (HVD) SCSI signal lines with power supply rails (+5 V, +12 V, +3.3 V), DIFFSENSE, TERMPWR, and four drive address bits into a single miniature D-style housing, eliminating the need for separate power and SCSI data cables. Seagate and other major drive manufacturers adopted SCA-2 widely for rack-mounted RAID enclosures during the late 1990s and early 2000s. HVD signalling on this connector supports cable lengths up to 25 m and bus speeds up to Ultra (20 MT/sec), though HVD was formally declared obsolete in SPI-3 (INCITS 336-2000).
| Pin | Name | Dir | Description |
|---|---|---|---|
| 1 | 12V | - | +12 VDC |
| 2 | 12V | - | +12 VDC |
| 3 | 12V | - | +12 VDC |
| 4 | 12V | - | +12 VDC |
| 5 | 3.3V | - | +3.3 VDC |
| 6 | 3.3V | - | +3.3 VDC |
| 7 | -DB(11) | IN/OUT | Data Bus 11 |
| 8 | -DB(10) | IN/OUT | Data Bus 10 |
| 9 | -DB(9) | IN/OUT | Data Bus 9 |
| 10 | -DB(8) | IN/OUT | Data Bus 8 |
| 11 | -I/O | OUT | Input/Output |
| 12 | -REQ | OUT | Request |
| 13 | -C/D | OUT | Control/Data |
| 14 | -SEL | IN/OUT | Select |
| 15 | -MSG | OUT | Message |
| 16 | -RST | IN/OUT | Reset |
| 17 | -ACK | IN | Acknowledge |
| 18 | -BSY | IN/OUT | Busy |
| 19 | -ATN | IN | Attention |
| 20 | -P_CRCA | ? | |
| 21 | -DB(7) | IN/OUT | Data Bus 7 |
| 22 | -DB(6) | IN/OUT | Data Bus 6 |
| 23 | -DB(5) | IN/OUT | Data Bus 5 |
| 24 | -DB(4) | IN/OUT | Data Bus 4 |
| 25 | -DB(3) | IN/OUT | Data Bus 3 |
| 26 | -DB(2) | IN/OUT | Data Bus 2 |
| 27 | -DB(1) | IN/OUT | Data Bus 1 |
| 28 | -DB(0) | IN/OUT | Data Bus 0 |
| 29 | -DB(P1) | ? | |
| 30 | -DB(15) | IN/OUT | Data Bus 15 |
| 31 | -DB(14) | IN/OUT | Data Bus 14 |
| 32 | -DB(13) | IN/OUT | Data Bus 13 |
| 33 | -DB(12) | IN/OUT | Data Bus 12 |
| 34 | 5V | - | Ground (Signal) |
| 35 | 5V | - | Ground (Signal) |
| 36 | 5V CHARGE | - | Ground (Signal) |
| 37 | SPINDLE SYNC | ? | Spindle Sync |
| 38 | RMT_START | ? | Remote Start |
| 39 | SCSI ID (0) | - | SCSI ID Bit 0 |
| 40 | SCSI ID (2) | - | SCSI ID Bit 2 |
| 41 | 12V GROUND | - | +12 VDC Ground |
| 42 | 12V GROUND | - | +12 VDC Ground |
| 43 | 12V GROUND | - | +12 VDC Ground |
| 44 | MATED 1 | ? | |
| 45 | 3.3V CHARGE | - | +3.3 VDC Charge |
| 46 | DIFFSNS | - | Differential Sense |
| 47 | +DB(11) | IN/OUT | Data Bus 11 |
| 48 | +DB(10) | IN/OUT | Data Bus 10 |
| 49 | +DB(9) | IN/OUT | Data Bus 9 |
| 50 | +DB(8) | IN/OUT | Data Bus 8 |
| 51 | +I/O | OUT | Input/Output |
| 52 | +REQ | OUT | Request |
| 53 | +C/D | OUT | Control/Data |
| 54 | +SEL | IN/OUT | Select |
| 55 | +MSG | OUT | Message |
| 56 | +RST | IN/OUT | Reset |
| 57 | +ACK | IN | Acknowledge |
| 58 | +BSY | IN/OUT | Busy |
| 59 | +ATN | IN | Attention |
| 60 | +P_CRCA | ? | |
| 61 | +DB(7) | IN/OUT | Data Bus 7 |
| 62 | +DB(6) | IN/OUT | Data Bus 6 |
| 63 | +DB(5) | IN/OUT | Data Bus 5 |
| 64 | +DB(4) | IN/OUT | Data Bus 4 |
| 65 | +DB(3) | IN/OUT | Data Bus 3 |
| 66 | +DB(2) | IN/OUT | Data Bus 2 |
| 67 | +DB(1) | IN/OUT | Data Bus 1 |
| 68 | +DB(0) | IN/OUT | Data Bus 0 |
| 69 | +DB(P1) | ? | |
| 70 | +DB(15) | IN/OUT | Data Bus 15 |
| 71 | +DB(14) | IN/OUT | Data Bus 14 |
| 72 | +DB(13) | IN/OUT | Data Bus 13 |
| 73 | +DB(12) | IN/OUT | Data Bus 12 |
| 74 | MATED 2 | ? | |
| 75 | 5V GROUND | - | +5 VDC Ground |
| 76 | 5V GROUND | - | +5 VDC Ground |
| 77 | ACTIVE LED OUT | ? | |
| 78 | DLYD_START | ? | |
| 79 | SCSI ID (1) | - | SCSI ID Bit 1 |
| 80 | SCSI ID (3) | - | SCSI ID Bit 3 |
Signals
- -DB(0) … -DB(15) — Negative (inverted) HVD differential data bus lines for the 16-bit wide SCSI bus; paired with corresponding +DB(n) lines to form complementary signal pairs.
- +DB(0) … +DB(15) — Positive HVD differential data bus lines; together with -DB(n) carry 16-bit wide data (DB0–DB7 are the lower byte; DB8–DB15 are the upper byte of the Wide SCSI bus).
- -DB(P1) / +DB(P1) (pins 29/69) — HVD differential pair for upper-byte parity (parity over DB8–DB15). Direction and description are not specified in this table; this is the wide-bus parity signal equivalent to DBP1 in 68-pin wide SCSI nomenclature.
- -P_CRCA / +P_CRCA (pins 20/60) — HVD differential pair for the CRC-A signal introduced in SPI-3/Ultra160 for cyclic redundancy checking of the data phase. Direction is not specified in this table.
- -I/O / +I/O — HVD differential pair; indicates transfer direction relative to the initiator (asserted = data flows to initiator).
- -REQ / +REQ — HVD differential pair; driven by the target to request each data byte transfer during the data phase.
- -C/D / +C/D — HVD differential pair; distinguishes command/status/message bytes (asserted) from data bytes (negated).
- -SEL / +SEL — HVD differential pair; used during Selection and Reselection phases to identify initiator and target on the bus.
- -MSG / +MSG — HVD differential pair; asserted during the Message phase to transfer bus management messages.
- -RST / +RST — HVD differential pair; a hard reset clears all SCSI devices on the bus when asserted.
- -ACK / +ACK — HVD differential pair; asserted by the initiator to acknowledge each REQ handshake during a data transfer.
- -BSY / +BSY — HVD differential pair; asserted by any device actively using the bus.
- -ATN / +ATN — HVD differential pair; asserted by the initiator to request a Message Out phase from the target.
- DIFFSNS (pin 46) — Differential Sense; used by LVD/MSE multimode devices to detect the bus signalling type (HVD vs LVD vs SE) and switch modes accordingly. On a pure HVD bus this pin is pulled to a level indicating HVD operation.
- SPINDLE SYNC (pin 37) — Optional synchronisation signal allowing the backplane to coordinate spindle rotation across multiple drives; direction and protocol are implementation-dependent.
- RMT_START (pin 38) — Remote Start; allows the backplane to command the drive to spin up independently of the SCSI bus, supporting staggered spin-up in multi-drive enclosures.
- DLYD_START (pin 78) — Delayed Start; a complementary spin-up control signal used alongside RMT_START for sequenced drive power-on.
- ACTIVE LED OUT (pin 77) — Drive activity LED output; driven by the drive to signal bus activity to the enclosure’s status panel.
- MATED 1 / MATED 2 (pins 44/74) — Connector presence detect signals; indicate that the drive is fully seated in the backplane slot, enabling hot-swap management logic.
- SCSI ID (0) … SCSI ID (3) (pins 39, 40, 79, 80) — Four address bits set by the backplane slot to assign the drive’s SCSI target ID (0–15) without requiring jumpers on the drive itself.
- 12V (pins 1–4) — +12 VDC supply for drive spindle motor.
- 3.3V (pins 5–6) — +3.3 VDC supply; presence depends on drive and backplane generation.
- 3.3V CHARGE (pin 45) — Pre-charge rail for the +3.3 V supply to limit inrush current during hot insertion.
- 5V CHARGE (pin 36) — Pre-charge rail for the +5 V supply to limit inrush current during hot insertion.
- 5V GROUND (pins 75–76) — Return path for the +5 VDC supply.
- 12V GROUND (pins 41–43) — Return path for the +12 VDC supply.
Notes
- Direction is device relative to bus (other devices).
- This connector carries the full 16-bit (Wide) HVD differential SCSI bus; all SCSI signal lines appear as complementary +/- pairs, consistent with HVD electrical signalling defined in SPI-2 (INCITS 302-1998).
- HVD signalling operates at 5 V logic levels using complementary line pairs per signal. Maximum supported bus speed is Ultra (20 MT/sec); HVD was formally deprecated in SPI-3 (INCITS 336-2000) and is electrically incompatible with LVD and SE buses.
- DIFFSNS (pin 46) is the Differential Sense pin used to distinguish bus signalling type. On an HVD bus it is driven to indicate HVD operation; on an LVD bus it is held low. Mixing HVD and LVD devices on the same bus will damage equipment.
- The SCA-2 connector integrates drive power (+5 V, +12 V, +3.3 V) and SCSI signals in a single housing, enabling tool-less hot-swap without separate power and data cabling.
- Staggered spin-up is managed via the RMT_START and DLYD_START pins, which allow the backplane controller to sequence drive spin-up and avoid simultaneous high inrush currents.
- SCSI ID bits 0–3 (pins 39, 40, 79, 80) are set by the physical backplane slot, providing automatic SCSI address assignment without drive jumpers.
- Two active terminators are required, one at each end of the SCSI bus segment; passive termination is not suitable for HVD at Ultra speeds.
- Original notes recorded against specific pins: pins 5 and 6 are listed as RESERVED/NC in some backplane implementations; pin 20 (-P_CRCA) is also documented in some sources as -DB(P0); pin 36 may be labelled 5 VOLT in some variants; pin 44 is sometimes identified as 12 V GROUND and pin 45 as RESERVED/NC; pin 46 is RESERVED/NC in certain earlier backplane revisions; pin 74 is in some sources labelled 5 V GROUND.
References
- SCSI Parallel Interface - 2 (SPI-2) Working Drafts Index
- SCSI Parallel Interface - 5 (SPI-5) Working Drafts Index
- LVD, SE, HVD SCSI Compatibility — Or Not (Paralan Expert Article)
- 68-Pin SCSI Cable Pinout for SE and HVD Interface
- SCSI FAQ Part 4 — Cabling, Termination, and Connector Technical Answers
- SCSI Revision Levels | Seagate Support