Universal synchronous receiver transmitter (USART) /universal asynchronous receiver transmit-
632/771 RM0401 Rev 3
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 Figure 215).
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 215. Word length programming
069
%LW %LW %LW %LW %LW %LW %LW %LW %LW
6WDUW
ELW
6WRS
ELW
1H[W
6WDUW
ELW
,GOHIUDPH
J S
%UHDNIUDPH
&ORFN
%LW %LW %LW %LW %LW %LW %LW %LW
&ORFN
ELWZRUGOHQJWK0ELWLVUHVHW6WRSELW
6WDUW
ELW
6WRS
ELW
6WDUW
ELW
6WDUW
ELW
3RVVLEOH
SDULW\ELW
1H[WGDWDIUDPH'DWDIUDPH
3RVVLEOH
SDULW\ELW
1H[WGDWDIUDPH'DWDIUDPH
6WRS
ELW
6WDUW
ELW
6WRS
ELW
6WDUW
ELW
/%&/ELWFRQWUROVODVWGDWDFORFNSXOVH
,GOHIUDPH
%UHDNIUDPH
1H[W
6WDUW
ELW