Sarjaportti

Sarjaportti, or serial port, is a computer interface used for serial communication, where data is transmitted one bit at a time over a single channel. Historically, it connected a wide range of peripherals such as modems, mice, printers, and terminals. The most common electrical standard is RS-232, defined for asynchronous transmission with start and stop bits and optional parity. Data rates vary widely, from about 110 baud to 115200 baud and beyond in some implementations. In addition to data lines, RS-232 provides control and status lines such as RTS, CTS, DTR, DSR, DCD, and RI, which enable handshaking and device signaling.

Physical connectors for the traditional PC serial port are mainly D-subminiature connectors, notably the 9-pin DE-9 (often referred to as DB-9) and the 25-pin DA-25 variants. Some systems use other connectors or pinouts, especially in industrial equipment. Modern adaptations may use TTL-level serial interfaces (0–5 V or 0–3.3 V) that require level shifting to RS-232 levels. In many contemporary devices, RS-232 ports have been supplemented or replaced by USB-to-serial adapters or integrated UARTs for embedded systems.

Despite the decline of native serial ports on new desktop PCs, sarjaportti remains in use in embedded hardware, industrial controllers, and network equipment consoles, where its simplicity and reliability are valued. The term “COM port” is still used in software interfaces to refer to these serial connections.