- Basic Information
- COM port is a cluster communication port, also known as serial port
- Microcomputers typically have two serial ports: COM1 (9-pin RS-232) and COM2 (25-pin RS-422)
- Maximum data rate is 115200bps
- Used for connecting serial mice and communication equipment
- Serial Communication Standards
- RS-232-C is most common, developed by EIA in 1970
- RS-422 extends transmission distance to 4000 feet with 10 receivers
- RS-485 adds multi-point and two-way communication capabilities
- USB is newer standard with speeds up to 40 Gbps
- USB Features
- Uses four-pin interface with data and power pins
- Maximum cable length is 5 meters
- Supports up to 127 devices in series
- Available in shielded (12Mbps) and unshielded (1.5Mbps) versions
- Applications
- Used for connecting external modems, plotters, and printers
- Main transmission control method in non-consumer applications
- Households typically don't use COM ports
- Industrial instruments use COM ports for standard communication