SCSI 68 pin differential

68-pin high-density D-Sub connector for HVD differential Wide SCSI, carrying 16-bit data and complementary +/- signal pairs on a 1.27 mm pitch housing.

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SCSI = Small Computer System Interface

SCSI-3 External Hi D-Sub (Differential)

SCSI 68 pin differential – 68-pin D-sub female 68 pin hi-density D-SUB female connector at the controller and devices.

SCSI 68 pin differential – 68-pin D-sub male 68 pin hi-density D-SUB male connector at the cable.

The 68-pin high-density D-Sub connector (DH68) is the standard external Wide SCSI connector defined in SCSI-2 (ANSI X3.131-1994) and carried forward through the SCSI-3 SPI series (INCITS 253 through INCITS 367-2003), covering transfer rates from Fast-Wide up to Ultra640. This variant uses High Voltage Differential (HVD) signalling, in which each signal is carried as a complementary pair of +/- lines on 5-volt logic, enabling cable runs of up to 25 metres. The HVD electrical variant was formally declared obsolete in SPI-3 (INCITS 336-2000), superseded by Low Voltage Differential (LVD) for new designs, though HVD hardware remained in service in legacy wide-SCSI installations. The connector body has two rows of 34 contacts at 1.27 mm pitch and carries a 16-bit data bus (DB0–DB15) with two parity lines, plus the full set of SCSI bus control signals and termination power.

PinNameDirDescription
1+DB12IN/OUT+Data Bus 12
2+DB13IN/OUT+Data Bus 13
3+DB14IN/OUT+Data Bus 14
4+DB15IN/OUT+Data Bus 15
5+DPB1IN/OUT+Data Bus Parity (odd Parity)
6GND-Ground
7+DB0IN/OUT+Data Bus 0
8+DB1IN/OUT+Data Bus 1
9+DB2IN/OUT+Data Bus 2
10+DB3IN/OUT+Data Bus 3
11+DB4IN/OUT+Data Bus 4
12+DB5IN/OUT+Data Bus 5
13+DB6IN/OUT+Data Bus 6
14+DB7IN/OUT+Data Bus 7
15+DPBIN/OUT+Data Bus Parity (odd Parity)
16DIFFSENSE??
17TERMPWRIN/OUTTermination Power
18TERMPWRIN/OUTTermination Power
19RES-Reserved
20+ATNIN+Attention
21GND-Ground
22+BSYIN/OUT+Bus is busy
23+ACKIN+Acknowledge
24+RSTIN/OUT+Reset
25+MSGOUT+Message
26+SELIN/OUT+Select
27+C/DOUT+Control or Data
28+REQOUT+Request
29+I/OOUT+In/Out
30GND-Ground
31+DB8IN/OUT+Data Bus 8
32+DB9IN/OUT+Data Bus 9
33+DB10IN/OUT+Data Bus 10
34+DB11IN/OUT+Data Bus 11
35-DB12IN/OUT-Data Bus 12
36-DB13IN/OUT-Data Bus 13
37-DB14IN/OUT-Data Bus 14
38-DB15IN/OUT-Data Bus 15
39-DPB1IN/OUT-Data Bus Parity (odd Parity)
40GND-Ground
41-DB0IN/OUT-Data Bus 0
42-DB1IN/OUT-Data Bus 1
43-DB2IN/OUT-Data Bus 2
44-DB3IN/OUT-Data Bus 3
45-DB4IN/OUT-Data Bus 4
46-DB5IN/OUT-Data Bus 5
47-DB6IN/OUT-Data Bus 6
48-DB7IN/OUT-Data Bus 7
49-DPBIN/OUT-Data Bus Parity (odd Parity)
50GND-Ground
51TERMPWRIN/OUTTermination Power
52TERMPWRIN/OUTTermination Power
53RES-Reserved
54-ATNIN-Attention
55GND-Ground
56-BSYIN/OUT-Bus is busy
57-ACKIN-Acknowledge
58-RSTIN/OUT-Reset
59-MSGOUT-Message
60-SELIN/OUT-Select
61-C/DOUT-Control or Data
62-REQOUT-Request
63-I/OOUT-In/Out
64GND-Ground
65-DB8IN/OUT-Data Bus 8
66-DB9IN/OUT-Data Bus 9
67-DB10IN/OUT-Data Bus 10
68-DB11IN/OUT-Data Bus 11

Signals

  • +DB0 / -DB0 through +DB7 / -DB7 — complementary HVD differential pairs for the lower data byte (bits 0–7); pins 7–14 carry the positive lines and pins 41–48 the negative lines.
  • +DB8 / -DB8 through +DB11 / -DB11 — upper data byte bits 8–11; positive lines on pins 31–34, negative on pins 65–68.
  • +DB12 / -DB12 through +DB15 / -DB15 — upper data byte bits 12–15; positive lines on pins 1–4, negative on pins 35–38.
  • +DPB / -DPB — differential parity pair for the lower byte (DB0–DB7); pins 15 and 49.
  • +DPB1 / -DPB1 — differential parity pair for the upper byte (DB8–DB15); pins 5 and 39.
  • DIFFSENSE — pin 16; sampled by LVD/MSE multimode devices to detect bus type; not driven by HVD devices. Its direction is undefined in an HVD-only context.
  • TERMPWR — termination power supply pins (17, 18, 51, 52); supply regulated voltage to bus terminators.
  • RES — reserved pins (19, 53); must not be connected.
  • +ATN / -ATN — differential Attention signal; asserted by an initiator to request a Message Out phase.
  • +BSY / -BSY — differential Bus Busy; wired-OR across all devices; indicates the bus is in use.
  • +ACK / -ACK — differential Acknowledge; handshake response from the initiator during a data transfer.
  • +RST / -RST — differential Reset; hard reset of all SCSI devices on the bus when asserted.
  • +MSG / -MSG — differential Message; target-driven phase indicator distinguishing message from command/data phases.
  • +SEL / -SEL — differential Select; used during selection and reselection phases.
  • +C/D / -C/D — differential Control/Data; driven by the target to indicate whether the current phase transfers commands/status (high) or data (low).
  • +REQ / -REQ — differential Request; target-driven handshake signal paired with ACK.
  • +I/O / -I/O — differential In/Out; driven by the target to indicate transfer direction relative to the initiator.
  • GND — signal ground return; distributed across pins 6, 21, 30, 40, 50, 55, 64.

Notes

  • Direction is device relative to bus (other devices).
  • HVD differential signalling uses complementary +/− line pairs for every signal, providing high noise immunity at 5-volt logic levels and supporting cable lengths up to 25 metres.
  • HVD was declared obsolete in SPI-3 (INCITS 336-2000); the maximum bus speed supported by HVD was Ultra (20 MT/sec). LVD (3.3 V) superseded HVD for all new Wide SCSI designs.
  • HVD and LVD are electrically incompatible and must never be mixed on the same bus segment; connecting an LVD device to an HVD bus can damage hardware.
  • The connector body has two rows of 34 contacts at 1.27 mm pitch. The female (socket) connector is fitted at the controller and devices; the male (plug) connector is at the cable end.
  • Exactly two terminators are required per bus segment, fitted at the two extreme ends only. HVD uses passive HVD terminators (differential terminator impedance: 122 ohms); active termination is not used with HVD.
  • TERMPWR pins (17, 18, 51, 52) supply power to bus terminators. Multiple TERMPWR pins are provided for redundancy and current capacity.
  • The DIFFSENSE pin (pin 16) is not driven by HVD devices but is monitored by any LVD/MSE multimode device that may be attached; its state determines whether the bus operates in LVD or SE mode on a multimode bus.
  • All SCSI bus signals in HVD mode are active-low on the positive (+) line of each pair.

References

Category:Buses Connectors