25 PIN D-SUB FEMALE at the Amiga.
The Amiga A500, A2000, and A3000 expose a 25-pin D-Sub female parallel port controlled by CIA-A (the MOS 8520 complex interface adapter), with port B pins PB0–PB7 carrying the bidirectional 8-bit data lines. Handshaking uses a two-line asynchronous protocol: the host asserts /STROBE (active low) to signal data-ready, and the peripheral returns /ACK to acknowledge receipt, which also triggers a level-2 interrupt on the Amiga. The interface is Centronics-compatible in function, though pin assignment and drive characteristics differ from the original Centronics specification. The later A1000 variant uses a DB25 male connector and a different signal on pin 1 (/DRDY instead of /STROBE) and carries +5 V on pin 23 rather than ground.
| Pin | Name | Dir | Description |
|---|---|---|---|
| 1 | /STROBE | OUT | Strobe |
| 2 | D0 | IN/OUT | Data Bit 0 |
| 3 | D1 | IN/OUT | Data Bit 1 |
| 4 | D2 | IN/OUT | Data Bit 2 |
| 5 | D3 | IN/OUT | Data Bit 3 |
| 6 | D4 | IN/OUT | Data Bit 4 |
| 7 | D5 | IN/OUT | Data Bit 5 |
| 8 | D6 | IN/OUT | Data Bit 6 |
| 9 | D7 | IN/OUT | Data Bit 7 |
| 10 | /ACK | IN | Acknowledge |
| 11 | BUSY | IN/OUT | Busy |
| 12 | POUT | IN/OUT | Paper Out |
| 13 | SEL | IN/OUT | Select (Shared with RS232 RING-indicator) |
| 14 | +5V PULLUP | OUT | +5 Volts DC (10 mA max) |
| 15 | n/c | - | Not connected. |
| 16 | /RESET | OUT | Reset |
| 17 | GND | - | Signal Ground |
| 18 | GND | - | Signal Ground |
| 19 | GND | - | Signal Ground |
| 20 | GND | - | Signal Ground |
| 21 | GND | - | Signal Ground |
| 22 | GND | - | Signal Ground |
| 23 | GND | - | Signal Ground |
| 24 | GND | - | Signal Ground |
| 25 | GND | - | Signal Ground |
Notes
- Direction is Computer relative Peripheral.
- This pinout applies to the A500, A2000, and A3000. The original A1000 uses a DB25 male connector with a different signal on pin 1 (/DRDY*) and +5 V on pin 23 instead of ground; standard printer cables designed for later Amigas must not be used on an A1000 without checking pin 23.
- Pin 14 provides a +5 V pullup supply (10 mA maximum); it is not a general-purpose power rail.
- /ACK on pin 10 is connected to the CIA-A FLAG input and triggers a level-2 interrupt, allowing software to be notified asynchronously when the peripheral has accepted a byte.
- Data pins D0–D7 are bidirectional, making this port suitable for general-purpose parallel I/O in addition to printer output.
Signals
- /STROBE — active-low pulse output asserted by the host after placing valid data on D0–D7 to signal data-ready to the peripheral
- D0–D7 — bidirectional 8-bit parallel data bus, driven by CIA-A port B (PB0–PB7)
- /ACK — active-low acknowledge input from the peripheral; receipt triggers a level-2 CPU interrupt on the Amiga
- BUSY — general-purpose I/O line; when used with a printer, indicates the device buffer is full and the host must wait
- POUT — paper-out status input from a printer peripheral
- SEL — device-select line; also shared with the RS-232 RING indicator signal
- +5V PULLUP — +5 V pullup supply on pin 14, limited to 10 mA; provides bias for open-collector peripheral signals
- /RESET — system reset output on pin 16; asserted when the Amiga resets, allowing peripherals to reinitialise
- GND — signal ground; pins 17–25 (pin 23 is ground on A500/A2000/A3000 — not +5 V as on the A1000)