Hardware serial port: Generally speaking, it is a serial port that meets RS232 or other serial communication connection protocols.

These protocols are not only communication protocols, but also interface protocols. For example, RS232 interface adopts 12V level signal.

Numbers signal each other. The characteristic of hardware serial port is that you should use a special serial line when connecting this device.

Connect the equipment and the main control machine.

Software serial port: generally speaking, it is a device that uses serial port in communication protocol, but in physical connection,

Do not necessarily follow the hardware protocol of serial port, such as simulating network communication on usb line and modeling on USB line.

Quasi-RS232 serial port. Its characteristic is that it can communicate with ready-made equipment and its interface is flexible. Like a lot.

The interfaces of ready-made modules such as GPRS and GPS are all serial ports, but this module claims to be 5V or 3.3V

Interface, then this can not be directly connected to the universal serial port, you need to go directly to TTL signal line and CPU.

Contact. The cpu can easily connect them by running a set of serial communication protocols.