A communication port serves as an endpoint for exchanging information between a computer and external devices. The term generally refers to two distinct concepts: a physical hardware interface or a logical network identifier.
1. Physical Interfaces (Hardware)
In hardware terms, a communication port is the physical socket or connector on a device. These ports act as gateways for data signals to enter and leave the equipment. Common examples found on power supplies and controllers include:
- USB: Universal Serial Bus for easy plug-and-play connection.
- Ethernet (LAN): RJ-45 port for network integration.
- RS-232C: Serial communication using a D-Sub 9-pin (DE-9) connector.
- GPIB: General Purpose Interface Bus, a standard in test and measurement.
To establish control, the appropriate cable must connect the physical ports of the computer and the power supply.
2. Logical Endpoints (Network Ports)
In the context of TCP/IP networking (Ethernet/LAN), a "port" is a logical, numbered endpoint within the operating system, not a physical component. It identifies a specific process or service running on a device.
When controlling LXI-compliant instruments or network-connected power supplies, logical ports are essential for directing commands. For example:
- VXI-11: Typically uses port 111.
- SCPI-RAW (Socket): Often uses port 5025.
Therefore, remote control over a LAN requires both a physical connection (cable to the LAN port) and a logical connection (targeting the correct IP address and port number).