ST STM32F446 Series

RM0390 Rev 4 799/1328
RM0390 Universal synchronous asynchronous receiver transmitter (USART)
845
25.4.1 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 Figure 280).
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.
Figure 280. Word length programming
069
%LW %LW %LW %LW %LW %LW %LW %LW %LW
6WDUW
ELW
6WRS
ELW
1H[W
6WDUW
ELW
,GOHIUDPH
J   S
%UHDNIUDPH
&ORFN

%LW %LW %LW %LW %LW %LW %LW %LW
&ORFN

ELWZRUGOHQJWK0ELWLVUHVHW6WRSELW
6WDUW
ELW
6WRS
ELW
6WDUW
ELW
6WDUW
ELW
3RVVLEOH
SDULW\ELW
1H[WGDWDIUDPH'DWDIUDPH
3RVVLEOH
SDULW\ELW
1H[WGDWDIUDPH'DWDIUDPH
6WRS
ELW
6WDUW
ELW
6WRS
ELW
6WDUW
ELW
/%&/ELWFRQWUROVODVWGDWDFORFNSXOVH
,GOHIUDPH
%UHDNIUDPH
1H[W
6WDUW
ELW