The audio and video connector arrangement varies across Amiga models. The A500 and A1000 provide composite video via RCA (CINCH) connectors, while the A2000 has no composite video output — only a header for an optional video modulator or Genlock adapter.

Composite Video

On the A1000, the composite video signal is a full FBAS (color composite) signal, compatible with most monitors. On the A500, cost savings resulted in a simpler BAS signal (monochrome composite only). Early A1000 models without a French keyboard output NTSC rather than PAL, which appears as black-and-white with interference lines on PAL monitors.

The video output is buffered through a transistor stage with a 75-ohm output impedance, providing permanent short-circuit protection.

Stereo Audio

Audio is carried on two RCA connectors on all models:

The outputs have a 1 Kohm output impedance and can be connected to any standard amplifier (AUX, TAPE, or CD input). They are short-circuit protected with an internal 36-ohm load resistor.

A1000 TV Modulator Connector

The A1000 has an additional 8-pin DIN audio/video connector (identical to the C64 modulator connector) intended for an RF modulator to connect a television. It carries both video and audio, plus a +12V supply for the modulator. The audio pins on this connector have a 1 Kohm output impedance but no internal load resistor, resulting in approximately four times the unloaded signal level compared to the RCA outputs.

The RGB connector is a 23-pin D-sub and is identical across all three Amiga models. It supports analog RGB monitors (like the Amiga monitor), digital RGB monitors, and special devices such as Genlock adapters.

Analog RGB Signals

For connection to an analog RGB monitor (such as the Commodore 1084), pins 3 (R), 4 (G), 5 (B), and 10 (CSYNC) are used. Denise's digital RGB output is converted to analog through a 4-bit DAC. The composite sync signal from Agnus is a mix of the vertical and horizontal sync signals. All four outputs have a 75-ohm output impedance and are transistor-buffered for short-circuit protection.

Digital RGB Signals

Pins 6–9 provide digital RGB signals for digital monitors. These come from Denise's digital RGB output, buffered through a 74HC244. The color signals are connected to Denise's upper bits (e.g., DB is connected to B3). All four signals have a 47-ohm output impedance at TTL levels.

Sync Signals

The HSY and VSY pins are bidirectional. In normal operation, they output horizontal and vertical sync from Agnus (TTL level, 47-ohm impedance, directly connected to Agnus pins). Sync signals are active-low — normally at 5V, going to 0V during sync pulses.

When Agnus's Genlock bit is enabled, these pins switch to input mode. The Amiga then synchronizes its video timing to external sync signals fed in through HSY and VSY — enabling genlocking with an external video source.

Zero Detect (ZD)

The ZD signal goes LOW whenever the currently displayed pixel is the background color (color register 0). This is used by Genlock adapters to key external video behind the Amiga's display. During vertical blank (VSY=0), ZD carries the GAUD bits (Genlock Audio Enable) from register $100 (BPLCON0), used as an audio switch by the Genlock interface.

External Clock

The C1U pin outputs a 3.58 MHz clock identical to the custom chip CLK signal. The XCLK and XCLKEN pins allow feeding an external master clock into the Amiga. All Amiga clocks derive from a 28 MHz oscillator, which can be replaced by an external clock via XCLK when XCLKEN is driven LOW. Pin 13 (GND) serves as the clock ground reference.

The Centronics parallel port uses a 25-pin D-sub connector. On the A500 and A2000, the pinout is PC-compatible — standard PC parallel printer cables work directly. The A1000 has a different pinout (notably pin 23 carries +5V instead of GND), so connecting a standard cable would cause a short circuit. A custom cable is required for A1000 printer connections.

CIA-A Connection Mapping

All parallel port signals are routed through CIA-A:

Transfer Protocol

When a valid data byte is placed on pins 2–9, the STROBE signal pulses LOW for 1.4 microseconds, signaling the printer that data is ready. The printer acknowledges by pulsing /ACK LOW for 1 microsecond. If the printer asserts BUSY, the Amiga waits until BUSY is deasserted before sending the next byte. POUT indicates paper-out, and SELECT indicates whether the printer is online (LOW) or offline (HIGH).

The parallel port is well-suited for expansion hardware such as sound digitizers, since all data pins can be programmed as either inputs or outputs through the CIA direction registers.

The serial port uses a 25-pin D-sub connector and provides a full RS-232 interface plus several non-standard signals.

RS-232 Signal Routing

The data lines TXD and RXD connect directly to Paula's serial data pins. The five handshaking signals are routed through CIA-B port A:

RS-232 signals are not connected directly to the CIAs — they pass through level converters (1488 output drivers, 1489A input receivers) that translate between TTL and RS-232 voltage levels. The output drivers use +12V to -5V swing. Input receivers accept -12V to +0.5V as LOW, and 3V to 25V as HIGH.

RS-232 conventions require handshake signals to be active HIGH, while TXD and RXD use negative logic for mark (1). Since the output drivers invert the signal, the corresponding CIA-B port bits are active-low — a 0 in the CIA register produces a HIGH on the RS-232 line.

Audio Pass-through

The AUDOUT pin carries the left audio channel with a 1 Kohm output impedance. The AUDIN pin (47-ohm impedance) feeds directly into Paula's right audio input (AUDR). An external audio signal entering through AUDIN passes through Paula's low-pass filter and emerges from the right audio RCA output.

A1000 Differences

The A1000 serial port has additional non-standard signals:

The external floppy connector is a 23-pin D-sub and uses the Shugart bus standard, supporting up to three external drives (DF1–DF3) in addition to the internal drive (DF0).

Motor Control via Flip-Flop

The MTRX signal does not directly control individual drive motors. Instead, each drive has a flip-flop that latches the MTRX state when its SEL line goes LOW. This allows independent motor control for each drive. For example, to start the internal drive's motor: set MTRX to 0, then pulse SEL0 LOW. The flip-flop captures the motor state; subsequently changing MTRX does not affect that drive until SEL0 is pulsed again.

The internal drive's flip-flop is on the motherboard. External drives require their own flip-flop circuit — typically built with a 74LS74 and a 74LS38 NAND gate.

Drive Identification

When the motor is off and a drive is selected, a special 32-bit identification mode is available. To initiate identification, the motor signal is briefly toggled to reset the drive's shift register. Then, each data bit is read by cycling SEL LOW and reading the RDY signal. This is repeated 32 times (MSB first). Since signals are active-low, the bits must be inverted.

In practice, only the first two bits need to be read: 00 = no drive, 11 = 3.5-inch, 01 = 5.25-inch.

CIA Connections

The four input signals (/CHNG, /WPRO, /TK0, /RDY) connect to CIA-A PA4–PA7. The eight output signals (/STEP, /DIR, /SIDE, /SEL0–/SEL3, /MTR) come from CIA-B PB0–PB7. Read/write data signals (/DKRD, /DKWD, /DKWE) connect directly to Paula. All signals use open-collector drivers (7407 type) and are active-low.

The two game ports are 9-pin D-sub connectors (DB-9) that accept mice, joysticks, trackballs, paddles, and light pens. Gameport 0 is on the left, Gameport 1 on the right. They are structurally identical except that Gameport 0 also connects to Agnus's light pen (LP) input.

Internal Chip Connections

All button and directional signals are active-low — internal switches connect the input pin to GND when pressed (HIGH = open, LOW = closed). The analog inputs (P0X, P0Y, P1X, P1Y) accept 470 Kohm variable resistors (potentiometers) connected between +5V and the input pin.

Power Protection

On the A1000, the +5V supply to both game ports is protected by a current limiter that separates continuous short-circuit current (400 mA) from peak surges (700 mA). Total current draw across both ports must not exceed 250 mA. This protection was removed on the A500 and A2000 models.

The expansion port is an 86-pin edge connector that exposes all important bus and control signals from the 68000 processor. It allows connection of memory expansions, accelerator boards, and other peripherals. On the A1000, it is located near the game ports behind a plastic cover. On the A500, it is on the underside of the unit. Pin spacing is 0.1 inch (2.54 mm).

The A2000 has a different arrangement: one 86-pin connector plus five 100-pin Zorro bus slots for expansion cards.

Clock Signals

The expansion port provides several clock references. CDAC runs at 7.16 MHz. /C1 and /C3 are 3.58 MHz signals with different phases. On the A2000, the 28.64 MHz master oscillator is also available (pin 9). The relationship between these clocks and the internal 7M, CCK, and CCKQ signals can be derived from their phase diagrams.

Configuration Signals

/OVR, XRDY, and PALOPE (A500/A1000 only) serve the auto-configuration protocol for expansion cards. Pins marked "extension" are reserved for future use. On the A2000, some have already been allocated (e.g., the 28 MHz clock).

Each Amiga connector carries one or more supply voltages. The total current budget depends on the model and how many ports are loaded simultaneously.

These values assume all connectors are loaded simultaneously. If some connectors are unused, their current budget is available to others. The A1000 power supply can deliver over 8A during a short circuit, so experimentation should be done with caution.

The A500 has a smaller power supply — external power is recommended for current-hungry expansions. The A2000 has a larger supply to support multiple expansion cards, including IBM emulation boards.

Note: the A500 provides -12V on its negative rail, while the A1000 provides -5V.