Universal synchronous asynchronous receiver transmitter (USART)
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DocID025202 Rev 7
If we consider an ideal case where the parameters DTRA, DQUANT, DREC and DTCL are
at 0%, the DWU max is 4.86 %. In reality, we need to consider at least the HSI inaccuracy.
Let us consider HSI inaccuracy = 1 %, t
WUUSART
= 3.125
μ
s (in case of wakeup from stop
mode, with the main regulator in Run mode).
DWU max = 4.86 % - 1 % = 3.86 %
Tbit min = 3.125
μ
s / (9
ₓ
3.86 %) = 9
μ
s
In these conditions, the maximum baud rate allowing to wakeup correctly from Stop mode is
1/9
μ
s = 111 Kbaud.
29.6
USART low-power modes
29.7 USART
interrupts
Table 158. Effect of low-power modes on the USART
Mode
Description
Sleep
No effect. USART interrupt causes the device to exit Sleep mode.
Stop
The USART is able to wake up the MCU from Stop mode when the UESM
bit is set and the USART clock is set to HSI or LSE.
The MCU wakeup from Stop mode can be done using either a standard
RXNE or a WUF interrupt.
Standby
The USART is powered down and must be reinitialized when the device
has exited from Standby mode.
Table 159. USART interrupt requests
Interrupt event
Event flag
Enable Control
bit
Transmit data register empty
TXE
TXEIE
CTS interrupt
CTSIF
CTSIE
Transmission Complete
TC
TCIE
Receive data register not empty (data ready to be read)
RXNE
RXNEIE
Overrun error detected
ORE
Idle line detected
IDLE
IDLEIE
Parity error
PE
PEIE
LIN break
LBDF
LBDIE
Noise Flag, Overrun error and Framing Error in multibuffer
communication.
NF or ORE or FE
EIE
Character match
CMF
CMIE
Receiver timeout
RTOF
RTOIE
End of Block
EOBF
EOBIE
Wakeup from Stop mode
WUF
(1)
WUFIE