30 pin Apple HDI-30 connector at the Apple computer, looking into cable-side connector.
The Apple HDI-30 is a proprietary 30-pin square connector developed by Apple for use on PowerBook laptop computers. It carries the full set of 8-bit narrow SCSI-1 signals — eight data lines, parity, and the standard control bus — within a compact, keyed housing that is mechanically incompatible with all industry-standard SCSI connectors. A dedicated adapter cable (the Apple SCSI Disk Adapter) is required to convert the HDI-30 interface to the standard 50-pin Centronics (CN50) external SCSI connector used by desktop peripherals. Single-Ended (SE) signalling at 5 V logic applies, consistent with the SCSI-1 and SCSI-2 specifications governing narrow parallel SCSI.
| Pin | Name | Dir | Description | Notes |
|---|---|---|---|---|
| 1 | SCSI-Mode | SCSI disk mode enable signal | Reserved for SCSI disk mode. | |
| 2 | Data0 | IN/OUT | Data bit 0 | Bit 0 of SCSI data bus |
| 3 | GND | - | Signal ground | Ground |
| 4 | Data1 | IN/OUT | Data bit 1 | Bit 1 of SCSI data bus |
| 5 | Termpwr +5 volts | IN/OUT | termination power | Termination power |
| 6 | Data2 | IN/OUT | Data bit 2 | Bit 2 of SCSI data bus |
| 7 | Data3 | IN/OUT | Data bit 3 | Bit 3 of SCSI data bus |
| 8 | GND | - | Signal ground | Ground |
| 9 | ACK | IN | Acknowledge | Handshake signal. When low acknowledges a request for data transfer |
| 10 | GND | - | Signal ground | Ground |
| 11 | Data4 | IN/OUT | Data bit 4 | Bit 4 of SCSI data bus |
| 12 | GND | - | Signal ground | Ground |
| 13 | GND | - | Signal ground | Ground |
| 14 | Data5 | IN/OUT | Data bit 5 | Bit 5 of SCSI data bus |
| 15 | GND | - | Signal ground | Ground |
| 16 | Data6 | IN/OUT | Data bit 6 | Bit 6 of SCSI data bus |
| 17 | GND | - | Signal ground | Ground |
| 18 | Data7 | IN/OUT | Data bit 7 | Bit 7 of SCSI data bus |
| 19 | PARITY | IN/OUT | Data parity | SCSI data bus parity bit |
| 20 | GND | - | Signal ground | Ground |
| 21 | REQ | OUT | Request | Request for a data transfer |
| 22 | GND | - | Signal ground | Ground |
| 23 | BUSY | IN/OUT | Busy | When active (low) indicates that the SCSI data bus is busy |
| 24 | GND | - | Signal ground | Ground |
| 25 | ATN | IN | Attention | When active (low) indicates an attention condition |
| 26 | C/D | OUT | Control/data | When active (low) indicates that data is on the SCSI bus. When high, indicates that control signals are on the bus |
| 27 | RST | IN/OUT | Reset | SCSI bus reset |
| 28 | MSG | OUT | Message | Indicates the message phase |
| 29 | SEL | IN/OUT | Select | SCSI select |
| 30 | I/O | OUT | Input/output | Controls the direction of data output. When high, data is input |
Signals
- SCSI-Mode — Reserved enable signal that activates SCSI disk mode on the PowerBook.
- Data0–Data7 — Eight active-low data lines forming the 8-bit narrow SCSI data bus (DB0–DB7).
- PARITY — Odd parity bit for the 8-bit data bus; active-low.
- ACK — Acknowledge; active-low handshake signal asserted by the initiator to confirm data transfer.
- REQ — Request; active-low handshake signal asserted by the target to request a data transfer.
- BUSY — Active-low signal indicating the SCSI bus is in use by a device.
- SEL — Select; used by the initiator to select a target or reselect an initiator.
- ATN — Attention; active-low signal from the initiator to request a Message Out phase.
- C/D — Control/Data; distinguishes between control (high) and data (low) phases on the bus.
- MSG — Message; active-low signal asserted during the Message phase of a SCSI transaction.
- RST — Reset; active-low signal that forces all devices on the bus to an initial state.
- I/O — Input/Output; controls transfer direction relative to the initiator (high = input to initiator).
- Termpwr +5 volts — Termination power supply line (+5 V) providing power to bus terminators.
- GND — Signal ground reference.
Notes
- The HDI-30 connector is a 30-pin square (5 rows of 6 contacts) proprietary Apple design; it is mechanically incompatible with all standard SCSI connectors.
- An Apple SCSI Disk Adapter cable is required to convert the HDI-30 to a standard 50-pin Centronics (CN50) external SCSI connector.
- The interface uses Single-Ended (SE) electrical signalling at 5 V logic, consistent with SCSI-1 and SCSI-2 narrow (8-bit) parallel SCSI.
- Maximum recommended cable length for SE Slow SCSI is 6 m; in practice, the short adapter cable supplied with the PowerBook keeps the total bus length within this limit.
- Termination rules apply as with any SCSI bus segment: exactly two terminators must be present at the two extreme ends. Passive termination (220/330 Ω) is acceptable at Slow SCSI (5 MB/sec) speeds.
- All SCSI-1/SCSI-2 signals are active-low; signal assertion drives the line towards 0 V.
- High Voltage Differential (HVD) and Low Voltage Differential (LVD) signalling are not applicable to this connector; it is exclusively a Single-Ended interface.