← Home · Devices

parallel.device — Centronics Parallel Port

Overview

parallel.device provides I/O for the Amiga's Centronics-compatible 25-pin parallel port. Primarily used for printers, it also serves as a general-purpose 8-bit data port for hardware projects, dongles, MIDI interfaces, and inter-machine transfers (Laplink-style).

The parallel port is directly connected to CIA-A Port B data register ($BFE101) with handshake lines on CIA-A and CIA-B.

flowchart LR
    APP["Application"] -->|"CMD_WRITE<br/>CMD_READ"| PAR["parallel.device"]
    PAR --> CIA["CIA-A Port B<br/>($BFE101)<br/>8 data bits"]
    CIA --> PORT["DB-25 Connector<br/>(pins 2-9 = data)"]
    PAR --> CIAB["CIA-B<br/>Handshake lines"]

    style PAR fill:#e8f4fd,stroke:#2196f3,color:#333
    style CIA fill:#c8e6c9,stroke:#2e7d32,color:#333

---

Hardware Pinout

Pin	Signal	Direction	Description
1	/STROBE	Output	Data strobe (active low)
2–9	D0–D7	I/O	8-bit bidirectional data
10	/ACK	Input	Acknowledge from printer
11	BUSY	Input	Printer busy
12	POUT	Input	Paper out
13	SELECT	Input	Printer selected
14–17	—	—	Reserved / unused
18–25	GND	—	Ground

---

Opening

struct MsgPort *parPort = CreateMsgPort();
struct IOExtPar *par = (struct IOExtPar *)
    CreateIORequest(parPort, sizeof(struct IOExtPar));

if (OpenDevice("parallel.device", 0, (struct IORequest *)par, 0))
{
    Printf("Cannot open parallel.device\n");
    /* Port may be in use by another application (printer, etc.) */
}

[!NOTE] Only one application can have the parallel port open at a time. If the port is busy (e.g., printer spooler has it), OpenDevice will fail. This is unlike serial.device which supports shared modes.

---

Commands

Code	Constant	Description
2	CMD_READ	Read bytes (bidirectional mode)
3	CMD_WRITE	Write bytes to the port
5	CMD_CLEAR	Clear internal buffers
7	CMD_RESET	Reset the device
8	CMD_FLUSH	Abort all pending I/O
9	PDCMD_QUERY	Get port status (busy, paper out, etc.)
10	PDCMD_SETPARAMS	Configure port parameters

Writing Data

/* Send data to the parallel port: */
char printData[] = "Hello, Printer!\r\n";
par->IOPar.io_Command = CMD_WRITE;
par->IOPar.io_Data    = printData;
par->IOPar.io_Length  = sizeof(printData) - 1;
DoIO((struct IORequest *)par);

if (par->IOPar.io_Error)
    Printf("Write error: %ld\n", par->IOPar.io_Error);

Querying Status

par->IOPar.io_Command = PDCMD_QUERY;
DoIO((struct IORequest *)par);

UBYTE status = par->io_Status;
if (status & IOPTF_PARBUSY)   Printf("Printer busy\n");
if (status & IOPTF_PAPEROUT)  Printf("Paper out\n");
if (status & IOPTF_PARSEL)    Printf("Printer selected\n");

Setting Parameters

/* Configure for custom use (e.g., no handshaking): */
par->IOPar.io_Command = PDCMD_SETPARAMS;
par->io_ParFlags = PARF_SHARED;      /* shared access (OS 2.0+) */
DoIO((struct IORequest *)par);

---

Direct Hardware Access

For hardware projects that need precise control (bypassing the device driver):

/* Direct CIA-A Port B access: */
volatile UBYTE *ciaaPrb  = (UBYTE *)0xBFE101;  /* data register */
volatile UBYTE *ciaaDdrb = (UBYTE *)0xBFE301;  /* data direction */

/* Set all 8 bits as output: */
*ciaaDdrb = 0xFF;

/* Write a byte: */
*ciaaPrb = 0x42;

/* Set as input: */
*ciaaDdrb = 0x00;
UBYTE value = *ciaaPrb;

[!CAUTION] Direct hardware access bypasses the OS completely. Do not mix direct register access with parallel.device operations — close the device first or don't open it at all.

---

Common Uses

Use Case	Method
Printer output	CMD_WRITE through printer.device (which opens parallel.device)
Hardware dongle	Direct CIA-A Port B register read
MIDI interface	Parallel-to-MIDI adapter with custom timing
Amiga-to-PC transfer	Laplink cable with ParNet or ParBench software
Sampling hardware	ADC/DAC connected to data lines

---

References

• NDK39: devices/parallel.h
• ADCD 2.1: parallel.device autodocs
• See also: serial.md — serial port I/O
• See also: cia_chips.md — CIA register details