The IBM External SCSI Burndy connector is a 60-pin High Density Centronics (HDCN60) proprietary connector used exclusively on IBM Micro Channel Architecture systems, specifically the PS/2 and RS/6000 product lines. It carries the same 8-bit narrow SCSI-1 signals as the standard Centronics 50-pin connector but in a physically incompatible housing manufactured by Burndy; it cannot be directly mated with any industry-standard SCSI cable or device. IBM introduced a companion 68-pin variant (HDCN68) for Wide SCSI-2 on later Micro Channel adapters, but the 60-pin connector remained the most common external narrow SCSI interface on those platforms. IBM discontinued both Burndy connector types after the PS/2 era, and all subsequent IBM systems reverted to conventional industry-standard SCSI connectors.
| Pin | Name | Dir | Description |
|---|---|---|---|
| 1 | GND | - | Ground |
| 2 | DB0 | IN/OUT | Data Bus 0 |
| 3 | GND | - | Ground |
| 4 | DB1 | IN/OUT | Data Bus 1 |
| 5 | GND | - | Ground |
| 6 | DB2 | IN/OUT | Data Bus 2 |
| 7 | GND | - | Ground |
| 8 | DB3 | IN/OUT | Data Bus 3 |
| 9 | GND | - | Ground |
| 10 | DB4 | IN/OUT | Data Bus 4 |
| 11 | GND | - | Ground |
| 12 | DB5 | IN/OUT | Data Bus 5 |
| 13 | GND | - | Ground |
| 14 | DB6 | IN/OUT | Data Bus 6 |
| 15 | GND | - | Ground |
| 16 | DB7 | IN/OUT | Data Bus 7 |
| 17 | GND | - | Ground |
| 18 | DPB | IN/OUT | Data Parity (odd Parity) |
| 19 | GND | - | Ground |
| 20 | GND | - | Ground |
| 21 | GND | - | Ground |
| 22 | GND | - | Ground |
| 23 | GND | - | Ground |
| 24 | GND | - | Ground |
| 25 | n/c | Not connected | |
| 26 | TERMPWR | IN/OUT | Termination Power |
| 27 | GND | - | Ground |
| 28 | GND | - | Ground |
| 29 | GND | - | Ground |
| 30 | GND | - | Ground |
| 31 | GND | - | Ground |
| 32 | /ATN | IN | Attention |
| 33 | GND | - | Ground |
| 34 | GND | - | Ground |
| 35 | GND | - | Ground |
| 36 | /BSY | IN/OUT | Busy |
| 37 | GND | - | Ground |
| 38 | /ACK | IN | Acknowledge |
| 39 | GND | - | Ground |
| 40 | /RST | IN/OUT | Reset |
| 41 | GND | - | Ground |
| 42 | /MSG | OUT | Message |
| 43 | GND | - | Ground |
| 44 | /SEL | IN/OUT | Select |
| 45 | GND | - | Ground |
| 46 | /C/D | OUT | Control/Data |
| 47 | GND | - | Ground |
| 48 | /REQ | OUT | Request |
| 49 | GND | - | Ground |
| 50 | /I/O | OUT | Input/Output |
| 51 | GND | - | Ground |
| 52 | res | Reserved | |
| 53 | res | Reserved | |
| 54 | res | Reserved | |
| 55 | res | Reserved | |
| 56 | res | Reserved | |
| 57 | res | Reserved | |
| 58 | res | Reserved | |
| 59 | res | Reserved | |
| 60 | res | Reserved |
Signals
- DB0–DB7 — Eight data bus lines carrying the 8-bit narrow SCSI data byte; all are active-low, bidirectional signals driven by either initiator or target depending on bus phase.
- DPB — Data parity bit (odd parity) covering the eight data lines DB0–DB7; bidirectional, asserted by the device driving the data bus.
- TERMPWR — Termination power supply line (nominally +5 V) used to power SCSI bus terminators; supplied by the host adapter or a terminator module.
- /ATN — Attention: asserted by the initiator to signal that it wishes to send a message to the target.
- /BSY — Busy: asserted by any device currently controlling the bus; bidirectional.
- /ACK — Acknowledge: asserted by the initiator to handshake each data or message byte transferred during REQ/ACK synchronous or asynchronous transfers.
- /RST — Reset: asserted by any device to perform a hard reset of the SCSI bus; bidirectional.
- /MSG — Message: driven by the target to indicate the current bus phase is a message phase (as opposed to data or command).
- /SEL — Select: used during arbitration and selection phases to address a specific target or re-select an initiator; bidirectional.
- /C/D — Control/Data: driven by the target to distinguish command, status, and message phases (asserted) from data phases (deasserted).
- /REQ — Request: asserted by the target during information transfer phases to request a handshake byte from the initiator.
- /I/O — Input/Output: driven by the target to define the direction of data transfer relative to the initiator (asserted = input to initiator, i.e. target sending data).
- n/c (pin 25) — Not connected; this pin is physically present in the housing but carries no signal.
- res (pins 52–60) — Reserved pins; no signal assignment was defined for these positions by IBM. They should not be driven.
- GND — Signal ground; odd-numbered pins 1–49 (except pin 25) are all ground, providing dense ground shielding between every active signal pin.
Notes
- The HDCN60 is physically and mechanically incompatible with the industry-standard Centronics 50-pin (CN50) and high-density 50-pin (DH50) SCSI connectors, despite carrying an electrically equivalent 8-bit narrow SCSI-1 signal set. An IBM-specific adapter cable is required to connect to standard SCSI peripherals.
- The connector is a Single-Ended (SE) interface operating at 5 V logic levels. Cable lengths must not exceed 6 m for Slow SCSI (5 MB/sec); in practice IBM RS/6000 and PS/2 installations were typically limited to much shorter runs.
- Termination rules follow standard SCSI practice: exactly two terminators are required, one at each extreme end of the bus segment. Passive termination (220/330 ohm resistor packs) is acceptable at Slow SCSI speeds; active termination is preferred for Fast SCSI (10 MB/sec) if used.
- IBM literature refers to this connector as the HDCN60 (High Density Centronics, 60-pin). The common name “Burndy” derives from the connector manufacturer; the two terms are interchangeable in IBM PS/2 and RS/6000 documentation.
- A related 68-pin variant (HDCN68) was used on IBM Micro Channel Wide SCSI-2 adapters but is a distinct connector. Both were discontinued with the end of the Micro Channel architecture.
- Pins 52–60 are reserved and were never assigned by IBM; they should be left unconnected on any adapter or cable.