34 pin IDC male connector at the computer and disk drive.
The Sun SPARCstation internal floppy interface uses a 34-pin IDC header that is physically similar to the standard PC floppy bus descended from the Shugart SA400 (introduced mid-1970s), but differs in several important ways. Sun workstations use an untwisted ribbon cable, with the drive jumpered as Drive 0 (DS0); the cable twist found on IBM PC cables — which swaps drive-select and motor-enable lines to allow all drives to be jumpered identically — is absent. Uniquely, the Sun variant adds media-sense signals on pins 6, 17, and 27 (FD_DRATE0_MSEN0, MSEN1, and MSEN0) that are not present on standard Shugart or IBM PC drives. Different SPARCstation models (e.g. SPARC-5 and Ultra-2) used different cable part numbers because pin 1 orientation differs between their motherboard connectors.
| Pin | Name |
|---|---|
| 1 | GND |
| 2 | FD_DENSEL |
| 3 | GND |
| 4 | 33_W_to_VCC |
| 5 | GND |
| 6 | FD_DRATE0_MSEN0 |
| 7 | N/C |
| 8 | FD_INDEX_L |
| 9 | GND |
| 10 | MTR0_L |
| 11 | GND |
| 12 | FD_DRV1_SEL_L |
| 13 | N/C |
| 14 | FD_DRV0_SEL_L |
| 15 | GND |
| 16 | FD_MTR1_L |
| 17 | MSEN1 |
| 18 | FD_DIR_L |
| 19 | GND |
| 20 | FD_STEP_L |
| 21 | GND |
| 22 | FD_WR_DAT_L |
| 23 | GND |
| 24 | FD_WR_GATE_L |
| 25 | GND |
| 26 | FD_TRK0_L |
| 27 | MSEN0 |
| 28 | FD_WR_PROT_L |
| 29 | GND |
| 30 | FD_RD_DAT_L |
| 31 | GND |
| 32 | FD_HD_SEL_L |
| 33 | GND |
| 34 | FD_DSK_CHNG_L |
Notes
- All odd-numbered pins are ground except pins 7, 13, 17, and 27, which carry N/C or signal lines specific to the Sun variant.
- The cable used is untwisted ribbon (unlike IBM PC cables, which apply a twist across pins 10–16). Sun drives are jumpered as Drive 0 by default; no cable twist is required or expected.
- Pin 4 (33_W_to_VCC) functions as a pull-up resistor connection rather than a conventional signal — it is not present on standard PC or Shugart drives.
- Pins 6, 17, and 27 carry media-sense signals (FD_DRATE0_MSEN0, MSEN1, MSEN0) used by the SPARCstation controller to detect media type; these pins are absent from standard Shugart/PC 34-pin interfaces.
- All active signal lines are active-LOW open-collector TTL: asserted (TRUE) = 0.0–0.4 V; deasserted (FALSE) = +2.5–+5.25 V.
- Different SPARCstation models use different internal cable part numbers (e.g. Sun 530-2067 for SPARC-5, 530-2138 for Ultra-2) due to differing pin 1 orientations on the board connector.
- A standard PC floppy drive is not a drop-in replacement for a Sun floppy drive without accounting for these signal and cabling differences.
Signals
- FD_DENSEL (pin 2) — Density select output from controller; selects between high-density and double-density recording.
- 33_W_to_VCC (pin 4) — Pull-up resistor connection to VCC; Sun-specific; not a conventional signal line.
- FD_DRATE0_MSEN0 (pin 6) — Combined data-rate select / media-sense 0; used by the Sun controller to detect media type and set data rate.
- FD_INDEX_L (pin 8) — Index pulse from drive; active-LOW pulse once per disk revolution indicating the start of track data.
- MTR0_L (pin 10) — Motor enable for drive 0; active-LOW signal from controller to spin up the drive motor.
- FD_DRV1_SEL_L (pin 12) — Drive 1 select; active-LOW signal from controller to select drive 1 on an untwisted cable.
- FD_DRV0_SEL_L (pin 14) — Drive 0 select; active-LOW signal from controller to select drive 0 (the default Sun drive).
- FD_MTR1_L (pin 16) — Motor enable for drive 1; active-LOW signal from controller.
- MSEN1 (pin 17) — Media-sense 1; Sun-specific signal returned by the drive to indicate media type; not present on standard PC drives.
- FD_DIR_L (pin 18) — Direction select; active-LOW signal from controller sets head step direction (inward or outward).
- FD_STEP_L (pin 20) — Step pulse from controller; each active-LOW pulse moves the read/write head one track.
- FD_WR_DAT_L (pin 22) — Write data; serial data stream from controller to drive during write operations.
- FD_WR_GATE_L (pin 24) — Write gate (write enable); active-LOW signal from controller enabling the write head.
- FD_TRK0_L (pin 26) — Track 00; active-LOW signal from drive indicating the head is positioned at track 0 (outermost track).
- MSEN0 (pin 27) — Media-sense 0; Sun-specific signal returned by the drive; works in conjunction with MSEN1 to encode media type.
- FD_WR_PROT_L (pin 28) — Write protect; active-LOW signal from drive indicating the inserted disc is write-protected.
- FD_RD_DAT_L (pin 30) — Read data; serial data stream from drive to controller during read operations.
- FD_HD_SEL_L (pin 32) — Head select (side select); active-LOW signal from controller selecting between side 0 (upper) and side 1 (lower) of a double-sided disc.
- FD_DSK_CHNG_L (pin 34) — Disk change; active-LOW signal from drive indicating that the disc has been ejected or changed since the last access.