34 PIN IDC MALE at the controller and CD-ROM
34 PIN IDC FEMALE at the cable
The Sony CD-ROM interface is a proprietary 8-bit parallel bus developed in the early 1990s for the CDU-31A (1×) and CDU-33A (2×) drives, which connected to an ISA host adapter card or compatible soundcard such as the Pro Audio Spectrum. Unlike the competing Mitsumi and Panasonic/MKE interfaces — both of which use 40-pin IDC connectors — the Sony interface uses a narrower 34-pin IDC ribbon cable, making it physically incompatible with those alternatives despite operating on similar ISA bus principles. All even-numbered pins carry ground; the odd pins carry RESET, an 8-bit data bus (DB7–DB0, MSB first at pin 3), control strobes (WE, RE), optional DMA handshake lines (ACK, REQ), an interrupt line (INT), two address bits (A1, A0), and a bus-enable signal (EN). These proprietary interfaces pre-date the ATAPI/IDE standardisation that became universal from the 4× generation onwards.
| Pin | Name | Description |
|---|---|---|
| 1 | RESET | Reset |
| 2 | GND | Ground |
| 3 | DB7 | Data Bit 7 |
| 4 | GND | Ground |
| 5 | DB6 | Data Bit 6 |
| 6 | GND | Ground |
| 7 | DB5 | Data Bit 5 |
| 8 | GND | Ground |
| 9 | DB4 | Data Bit 4 |
| 10 | GND | Ground |
| 11 | DB3 | Data Bit 3 |
| 12 | GND | Ground |
| 13 | DB2 | Data Bit 2 |
| 14 | GND | Ground |
| 15 | DB1 | Data Bit 1 |
| 16 | GND | Ground |
| 17 | DB0 | Data Bit 0 |
| 18 | GND | Ground |
| 19 | WE | Write Enable |
| 20 | GND | Ground |
| 21 | RE | Read Enable |
| 22 | GND | Ground |
| 23 | ACK | Data Acknowledge For DMA |
| 24 | GND | Ground |
| 25 | REQ | Data Request For DMA |
| 26 | GND | Ground |
| 27 | INT | Interrupt |
| 28 | GND | Ground |
| 29 | A1 | Address Bit 1 |
| 30 | GND | Ground |
| 31 | A0 | Address Bit 0 |
| 32 | GND | Ground |
| 33 | EN | Bus Enable |
| 34 | GND | Ground |
Notes
The connector at both the controller card and the CD-ROM drive is a 34-pin IDC male header; the ribbon cable uses a 34-pin IDC female connector on each end. Although the 34-pin count matches the standard floppy-disk ribbon cable, the Sony interface is electrically incompatible with floppy drives. The CDU-33A-81 variant reportedly uses a floppy-style ribbon arrangement rather than the standard 34-pin IDC header. In addition to the internal 34-pin interface connector (CNJ202 on the drive’s MA-board), the Sony adapter card exposes a 50-pin external expansion connector (CN4). Analogue audio output uses a separate 4-pin cable, not the interface ribbon. The drive’s default I/O base address is 360h, IRQ channel 2, and DRQ channel 3; power requirements are +5 V (logic) and +12 V (spindle motor). The Linux kernel driver for this interface is cdu31a.
Signals
- RESET — Active signal that resets the drive; asserted by the host controller.
- DB7–DB0 — 8-bit parallel data bus; DB7 (MSB) appears at pin 3, decreasing to DB0 at pin 17. Data is transferred MSB-first on odd pins.
- WE — Write Enable; host asserts to write data or command bytes to the drive.
- RE — Read Enable; host asserts to read status or data bytes from the drive.
- ACK — DMA Acknowledge; handshake signal returned by the DMA controller to confirm acceptance of a DMA transfer request.
- REQ — DMA Request; asserted by the drive to request a DMA transfer cycle from the host.
- INT — Interrupt; asserted by the drive to signal the host that attention is required (command completion, error, etc.).
- A1, A0 — Address bits selecting the internal register within the drive to be accessed.
- EN — Bus Enable; enables the drive’s data bus drivers onto the shared interface bus.
- GND — All even pins (2–34) are ground.