The difference between UART and Usart

UART and Usart are single-chip serial communication, the difference between them is as follows:

First look at the name:

Uart:universal asynchronous receiver and transmitter universal asynchronous receiver/Sender
Usart:universal synchronous asynchronous receiver and transmitter universal synchronous/Asynchronous Receiver/Sender

As can be seen from the name, Usart on the basis of the UART added synchronization function, that is, Usart is the enhancement of the UART, the fact is true.     But where is the concrete reinforcement? In fact, when we use Usart in asynchronous communication, it is no different from the UART, but when used in synchronous communication, the difference is obvious: we all know that synchronous communication requires a clock to trigger data transmission, that is, Usart relative to the UART is one of the difference is to provide active clock. such as STM32 's Usart can provide a smart card interface for clock support ISO7816.