Universal Sync/Asynchronous Receiver/Transmitter, #include <aery32/usart.h>

USART module can be used for several kind of communication. The RS-232 serial communication with a personal computer (PC) is likely the most common one.


There’s also a class driver for serial port communication. Skip to Serial Port class driver.


To initialize the USART0 for serial communication call

usart_init_serial(usart0, USART_PARITY_NONE, USART_STOPBITS_1);

Serial communication initialized with no parity and 1 stop bits is the default setup for most of the devices, so you may omit the last two parameters if you like. Other options are EVEN, ODD, MARKED and SPACE for parity, and 1p5 and 2 for stop bits.

After then you have to set up the baud rate. The baud rate is derived from clock of the peripheral bus B (PBA) or at external pin. This source clock is then diveded in divider for integer part and additionally for fractional part to achieve even smaller baudrate error. Assuming that the PBA bus speed is 66 MHz we have to divide it by 71 to get the baud rate of 115 200 bit/s (error 0.8%).

usart_setup_speed(usart0, USART_CLK_PBA, 71, 0);

The last parameter is the divider for the fractional part which could have been also omitted because it was set to zero. We could have set the fractional part here to 5 to get even smaller baud rate error (0.16%).

At last you have to enable RX and TX channels separately for receiving and transmitting data