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Serial port, COM port, UART port, TTL, RS-232, RS-485 difference

First, the serial port, UART port, COM port, and USB port refer to the physical interface form (hardware). TTL, RS-232, and RS-485 refer to the level standard (electrical signal).
Serial port: The serial port is a generic term. UART, TTL, RS232, and RS485 all follow a similar communication timing protocol, so they are commonly referred to as serial ports.
UART interface: Universal Asynchronous Receiver/Transmitter, UART is the logic circuit for serial port transceiver. This part can be integrated into a chip or embedded in other chips as a module. There will be UART module in MCU, SOC and PC. .
COM port: specifically refers to the serial communication port of the D-SUB form factor (a connector structure, the VGA interface connector is also D-SUB) on a desktop computer or some electronic devices, and uses serial communication timing and RS232 logic power. level.
USB port: Universal serial bus, and serial port are two concepts. Although it is also serial communication, since the USB communication timing and signal level are completely different from the serial port, it has nothing to do with the serial port. USB is a high-speed communication interface for PCs to connect various peripherals, U disk, mouse and keyboard, mobile hard disk, and of course, "USB to serial port" module. (USB to serial port module, is the UART module of USB interface)
TTL, RS232, RS485 are a representation of logic levels
TTL: TTL refers to the bipolar transistor logic circuit. Many "USB to TTL" modules on the market are actually "USB to TTL level serial port" modules. This signal 0 corresponds to 0V, and 1 corresponds to 3.3V or 5V. Compatible with IO level of single chip microcomputer and SOC. However, the actual level is not necessarily the TTL level, because most of the digital logic is now done in CMOS technology, but the TTL is used. When we perform serial communication, the basics that come out directly from the microcontroller are all TTL levels.

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