Several solutions of single USB to multi-serial port

 
Serial port (Uart) is a very commonly used interface in embedded, but nowadays computers do not have a hardware serial port.

Generally, the serial port is expanded by means of bus expansion such as USB to serial port or PCIE.

USB to serial port is a very common one. Commonly used USB-to-serial chips include CH340/341, CP2102, PL2302, etc.

However, these chips are all USB-to-single serial ports. If multiple serial ports are required, multiple USB ports need to be occupied. Today, I will introduce the solution of single USB port to multiple serial ports.

1. Dedicated chip

Companies that started with USB-related chips have many USB-to-serial chips, including USB-to-multiple serial-port chips. For example, CH342 is a USB-to-dual serial port chip:
 
CH9344 is a USB to 4 serial port chip
 
There is also a USB to 8 serial port chip, CH348
 
This solution is very simple to use and can be implemented with just one chip.

2. USB HUB

The function of USB HUB is to expand one USB port into multiple USB ports, so that when using multiple USB-to-serial chips, there is no need to worry about insufficient USB ports.

Commonly used USB HUB chips include GL850G, FE1.1S, etc., which can realize USB one-to-four, and with CH340 and other chips, can realize single USB to multi-serial ports.
 
USB HUB chips can be cascaded to realize the expansion of multiple USB ports. It should be noted that these USB ports share the bandwidth of one port, but for applications such as serial ports with a small amount of data, there is no problem.

3. Software implementation

We know that many microcontrollers have a USB interface, which can realize the function of a USB virtual serial port. In general, a virtual serial port is used to use

Taking STM32F072 as an example, the USB port of this microcontroller supports 8 output and 8 input endpoints.

Through the configuration of USB device descriptors, input and output endpoints, etc., USB virtual multiple serial ports can be realized.

This method only needs one single chip, which is realized by software, which is more flexible to use, and the software can also realize other functions.

USB to 4 serial port CH9344 

USB to 8 serial port CH348

Single USB to multi-serial port