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First of all, serial port, UART port, COM port, USB port refers to the physical interface form (hardware). TTL, RS-232, RS-485 refers to the level standard (electrical signal).
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Serial port: Serial port is a generic term, UART, TTL, RS232, RS485 all follow similar communication timing protocols, so they are generally called serial ports.
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UART interface: Universal Asynchronous Receiver\/Transmitter (UART), UART is a logical circuit for serial port transceiver, this part can be independent into a chip, or as a module embedded in other chips, MCU, SOC, PC will have UART module.
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COM port: Especially refers to the serial communication port of the D-SUB shape (a connector structure, the connector of the VGA interface is also D-SUB) on the desktop computer or some electronic devices, which applies the serial communication timing and the logic level of RS232.
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USB port: universal serial bus, and serial port is completely two concepts. Although it is also serial communication, because the communication timing and signal level of USB are completely different from the serial port, it has nothing to do with the serial port. USB is a high-speed communication interface, used for PC to connect a variety of peripherals, U disk, keyboard and mouse, mobile hard disk, of course, also including the \"USB to serial port\" module. (USB to serial port module, that is, UART module of USB interface)
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TTL, RS232, RS485 are all logical level representations
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TTL: TTL refers to bipolar triode logic circuit, many \"USB to TTL\" modules on the market, is actually \"USB to TTL level serial port\" module. This signal 0 corresponds to 0V, and 1 corresponds to 3.3V or 5V. Compatible with IO level of MCU and SOC. However, the actual TTL level is not necessarily, because most of the digital logic is now done by the CMOS process, just using the TTL statement. When we carry out serial communication, the basic TTL level directly from the MCU is