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COM port (DE-9 connector). COM (communication port) [1] [2] is the original, yet still common, name of the serial port interface on PC-compatible computers. It can refer not only to physical ports, but also to emulated ports, such as ports created by Bluetooth or USB adapters.
Not all bit rates are possible with all serial ports. Some special-purpose protocols such as MIDI for musical instrument control, use serial data rates other than the teleprinter standards. Some serial port implementations can automatically choose a bit rate by observing what a connected device is sending and synchronizing to it.
Serial ports send and receive one bit at a time via a single wire pair (Ground and +/-). After ports are connected, they typically require handshaking, where transfer type, transfer rate, and other necessary information is shared before data is sent. Hot-swappable ports can be connected while equipment is running. Almost all ports on personal ...
RS-232 serial ports (25-pin, ready to connect to a modem, yet some manufacturer-specific pin usage extended the standard, e.g. for use with 20-mA current loops) 24 lines (or possibly 25 – sometimes a special status line) of 72 or 80 characters of text (80 was the same as IBM punched cards). Later models sometimes had two character-width settings.
Frequent use of a serial port is for a direct computer-to-computer connection. This requires an adapter called a null modem, which isn't actually a modem in the traditional sense, but rather a connector plug that simply crosses the complementary pins on two serial ports so the two sides can communicate. A null modem typically connects the DTR ...
A software-based virtual serial port presents one or more virtual serial port identifiers on a PC which other applications can see and interact with as if they were real hardware ports, but the data sent and received to these virtual devices is handled by software that manipulates the transmitted and received data to grant greater functionality.
In computing, an interface is a shared boundary across which two or more separate components of a computer system exchange information. The exchange can be between software, computer hardware, peripheral devices, humans, and combinations of these. [1]
For example, on the original IBM PC, a male D-sub was an RS-232-C DTE port (with a non-standard current loop interface on reserved pins), but the female D-sub connector on the same PC model was used for the parallel "Centronics" printer port. Some personal computers put non-standard voltages or signals on some pins of their serial ports.