Usart Character Description; Figure 215. Word Length Programming - ST STM32F410 Reference Manual

Universal synchronous receiver transmitter (USART) /universal asynchronous receiver transmit-
24.4.1

USART character description

Word length may be selected as being either 8 or 9 bits by programming the M bit in the
USART_CR1 register (see
The TX pin is in low state during the start bit. It is in high state during the stop bit.
An Idle character is interpreted as an entire frame of "1"s followed by the start bit of the
next frame that contains data (The number of "1" 's will include the number of stop bits).
A Break character is interpreted on receiving "0"s for a frame period. At the end of the
break frame the transmitter inserts either 1 or 2 stop bits (logic "1" bit) to acknowledge the
start bit.
Transmission and reception are driven by a common baud rate generator, the clock for each
is generated when the enable bit is set respectively for the transmitter and receiver.
The details of each block is given below.
632/771
Figure 215).

Figure 215. Word length programming

RM0401 Rev 3