27.3.3 Communication Modes

The USART is a flexible peripheral that supports multiple different communication protocols. The available modes of operation can be split into two groups: Synchronous and asynchronous communication.

The synchronous communication relies on one device on the bus to be the host, providing the rest of the devices with a clock signal through the XCK pin. All the devices use this common clock signal for both transmission and reception, requiring no additional synchronization mechanism.

The device can be configured to run either as a host or a client on the synchronous bus.

The asynchronous communication does not use a common clock signal. Instead, it relies on the communicating devices to be configured with the same baud rate. When receiving a transmission, the hardware synchronization mechanisms are used to align the incoming transmission with the receiving device peripheral clock.

Four different modes of reception are available when communicating asynchronously. One of these modes can receive transmissions at twice the normal speed, sampling only eight times per bit instead of the normal 16. The other three operating modes use variations of synchronization logic, all receiving at normal speed.