USART General description

The USART receiver block monitors the serial input line, Un_RXD, for valid input. The receiver shift register assembles characters as they are received, after which they are passed to the receiver buffer register to await access by the CPU.

The USART transmitter block accepts data written by the CPU and buffers the data in the transmit holding register. When the transmitter is available, the transmit shift register takes that data, formats it, and serializes it to the serial output, Un_TXD.

The Baud Rate Generator block divides the incoming clock to create a 16x baud rate clock in the standard asynchronous operating mode. The BRG clock input source is the shared Fractional Rate Generator that runs from the common USART peripheral clock U_PCLK).

In synchronous slave mode, data is transmitted and received using the serial clock directly. In synchronous master mode, data is transmitted and received using the baud rate clock without division.

Status information from the transmitter and receiver is saved and provided via the Stat register. Many of the status flags are able to generate interrupts, as selected by software.

Note: The fractional value and the USART peripheral clock are shared between all USARTs.


U_PCLK = UARTCLKDIV/(1+MULT/DIV)

USART block diagram


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