Apple IIgs Disk Drive Port - DB-19 Pin connector
19 pin D-SUB female connector at the computer.
19 pin D-SUB male connector at the cable.
The Apple external disk drive port uses a 19-pin D-subminiature (DB-19) connector, introduced with the UniDisk and carried forward on the Apple IIc, IIc Plus, IIgs, and all classic Macintosh models from the 128K through the IIvx/Performa 600. Signals are driven by the IWM (Integrated Woz Machine) controller IC, which manages stepper-motor phase lines, serial GCR read/write data, and drive-enable outputs. The pin assignment shown here matches the Apple IIgs variant, which repurposes pin 4 as the 3.5DISK media-type select and pin 16 as HDSEL (head select) to support both 5.25-inch and 3.5-inch drives; these two pins differ from the Apple IIc, where pin 4 is GND and pin 9 carries the EXTINT* external-interrupt signal rather than a drive-select line.
| Pin | Signal | Description |
|---|---|---|
| 1 | GND | Ground |
| 2 | GND | Ground |
| 3 | GND | Ground |
| 4 | 3.5DISK | 3.5 or 5.25-inch drive select. |
| 5 | -12V | -12 volt supply. |
| 6 | +5V | +5 volt supply. |
| 7 | +12V | +12 volt supply. |
| 8 | +12V | +12 volt supply. |
| 9 | DR2 | Drive 2 Select. |
| 10 | WRPROT | Write protect input. |
| 11 | PHASE0 | Motor Phase 0 output. |
| 12 | PHASE1 | Motor Phase 1 output. |
| 13 | PHASE2 | Motor Phase 2 output. |
| 14 | PHASE3 | Motor Phase 3 output. |
| 15 | WREQ | Write request. |
| 16 | HDSEL | Head Select. |
| 17 | DR1 | Drive 1 select. |
| 18 | RDDATA | Read data input. |
| 19 | WDATA | Write data output. |
Signals
- GND — Signal ground; pins 1–3 provide the ground return for all drive signals and power rails.
- 3.5DISK — Media-type select (IIgs-specific on pin 4); pulled low by the drive to indicate a 3.5-inch mechanism; absent on the Apple IIc, where pin 4 is an additional GND.
- -12V — Negative supply rail for drive electronics; for disk drive use only.
- +5V — Logic supply for drive electronics; for disk drive use only.
- +12V — Motor supply; provided on two pins (7 and 8) for current capacity; for disk drive use only.
- DR2 — Drive 2 select (IIgs pin 9); selects the second daisy-chained drive. On the Apple IIc this pin carries EXTINT* (external interrupt) instead.
- WRPROT — Write-protect status input; asserted by the drive when the write-protect notch is covered.
- PHASE0–PHASE3 — Stepper-motor phase control outputs (pins 11–14); also referred to as CA0, CA1, CA2, and LSTRB in Macintosh/IWM register-access nomenclature when used with 3.5-inch Sony drives.
- WREQ — Write request (active low); when asserted, the IWM signals that write data is available and the drive may accept it.
- HDSEL — Head select for double-sided 3.5-inch drives; selects between the upper and lower read/write heads.
- DR1 — Drive 1 (internal drive) enable/select.
- RDDATA — Serial read data input; carries GCR-encoded data from the drive to the IWM.
- WDATA — Serial write data output; carries GCR-encoded data from the IWM to the drive.
Notes
- Power rails (-12 V, +5 V, +12 V) on this port are for disk drive use only and must not be used to power other peripherals.
- The DB-19 connector at the computer is female (socket); the cable plug is male. Pin numbering on the DB-19 does not correspond directly to wire numbers in the cable.
- The IIgs port accepts both 5.25-inch and 3.5-inch Apple II drives; the 3.5DISK line (pin 4) and HDSEL (pin 16) are required for correct 3.5-inch operation.
- The Apple IIc DB-19 port differs on pins 4 (GND instead of 3.5DISK) and 9 (EXTINT* instead of DR2) and pin 16 (NC instead of HDSEL); adapting an IIc cable to an IIgs controller requires attention to these differences.
- Drives are daisy-chained via the second connector on the drive chassis; the drive-select lines route accordingly through the chain.