Difference UART/USART

What is the difference between devices /dev/tty-x and /dev/ttySx?

I’m ne to this all and I also like to know the difference.

Can someone explain?

I am not an expert in this subject yet. However, the “S” stands for “sychronous”, meaning that USART and UART wirings are different.

In practice, USART ports require, in addition to VCC, GND, RX and TX, two more signals: CS and CLK. These are clock references.

Another consequence is the baud rate accepted by USART ports, which is meaningfully higher than UART ports’ limit. The boundary between them is around 115200 baud.

Reference: http://www.firmcodes.com/difference-uart-usart/