Commodore Amiga 4000 Serial Port Pin Configuration
This article provides a comprehensive technical breakdown of the serial port pin configuration found on the Commodore Amiga 4000 computer. It outlines the specific DB25 connector layout, details the function of each signal pin, and offers essential voltage specifications required for interfacing with external peripherals such as modems, printers, or null-modem cables.
The Commodore Amiga 4000 utilizes a standard DB25 male connector for its serial communications interface. This port is driven by the system’s UART logic, allowing for asynchronous serial communication compatible with RS-232 standards. When building custom cables or troubleshooting connectivity issues, understanding the specific pin assignment is critical to ensure proper data transmission and handshaking between the Amiga and connected devices.
Pinout Table
The following table details the pin assignments for the Amiga 4000 serial port. The connector is viewed from the back of the computer with the pins facing away from the user.
| Pin Number | Signal Name | Direction | Description |
|---|---|---|---|
| 1 | Shield | - | Frame Ground / Shield |
| 2 | TxD | Output | Transmit Data |
| 3 | RxD | Input | Receive Data |
| 4 | RTS | Output | Request To Send |
| 5 | CTS | Input | Clear To Send |
| 6 | DSR | Input | Data Set Ready |
| 7 | GND | - | Signal Ground |
| 8 | DCD | Input | Data Carrier Detect |
| 20 | DTR | Output | Data Terminal Ready |
| 22 | RI | Input | Ring Indicator |
Signal Specifications
The serial port operates using RS-232 voltage levels. Logic 0 (Space) is represented by a positive voltage between +3V and +25V, typically around +12V. Logic 1 (Mark) is represented by a negative voltage between -3V and -25V, typically around -12V. Pin 7 serves as the common signal ground for all data and control lines, while Pin 1 connects to the chassis ground for shielding purposes.
Wiring Considerations
When connecting the Amiga 4000 to a standard PC or modem, a null-modem cable is often required if both devices are configured as DTE (Data Terminal Equipment). In a null-modem configuration, the TxD and RxD lines are crossed, as are the handshaking lines such as RTS/CTS and DTR/DSR. It is important to ensure that the signal ground (Pin 7) is connected directly through the cable to maintain a common reference voltage. Users should verify peripheral compatibility before connecting to avoid potential damage to the CIA chip or serial controller logic.