USART is one of the primitive inter-device communication protocols. It is no different from USART except for the voltage levels and some additional signals. Commonly MAX232 IC is used to translate the voltage level. MAX232 is a simple voltage translator buffer that converts +12/-12V of RS232 to 5/0V for USART. Other specifications are similar for USART and RS232. To make communication between MCU and PC via COM port you obviously need a COM port and Max232 bridge.
