ST STM32L4 5 Series User Manual

Universal synchronous asynchronous receiver transmitter (USART) RM0351
1320/1830 DocID024597 Rev 5
40.5.5 Tolerance of the USART receiver to clock deviation
The asynchronous receiver of the USART works correctly only if the total clock system
deviation is less than the tolerance of the USART receiver. The causes which contribute to
the total deviation are:
• DTRA: Deviation due to the transmitter error (which also includes the deviation of the
transmitter’s local oscillator)
• DQUANT: Error due to the baud rate quantization of the receiver
• DREC: Deviation of the receiver’s local oscillator
• DTCL: Deviation due to the transmission line (generally due to the transceivers which
can introduce an asymmetry between the low-to-high transition timing and the high-to-
low transition timing)
where
DWU is the error due to sampling point deviation when the wakeup from Stop mode is
used.
when M[1:0] = 01:
when M[1:0] = 00:
when M[1:0] = 10:
t
WUUSART
is the time between detection of the wakeup event and the instant when
clock (requested by the peripheral) and regulator are ready.
The USART receiver can receive data correctly at up to the maximum tolerated
deviation specified in Table 235 and Table 235 depending on the following choices:
• 9-, 10- or 11-bit character length defined by the M bits in the USART_CR1 register
• Oversampling by 8 or 16 defined by the OVER8 bit in the USART_CR1 register
• Bits BRR[3:0] of USART_BRR register are equal to or different from 0000.
• Use of 1 bit or 3 bits to sample the data, depending on the value of the ONEBIT bit in
the USART_CR3 register.
Table 235. Tolerance of the USART receiver when BRR [3:0] = 0000
M bits
OVER8 bit = 0 OVER8 bit = 1
ONEBIT=0 ONEBIT=1 ONEBIT=0 ONEBIT=1
00 3.75% 4.375% 2.50% 3.75%
01 3.41% 3.97% 2.27% 3.41%
10 4.16% 4.86% 2.77% 4.16%
DTRA DQUANT DREC DTCL DWU++++USART receiver′ s tolerance<
DWU
t
WUUSART
11 Tbit×
---------------------------
=
DWU
t
WUUSART
10 Tbit×
---------------------------
=
DWU
t
WUUSART
9Tbit×
---------------------------
=

ST STM32L4 5 Series Specifications

General

Brand	ST
Model	STM32L4 5 Series
Category	Microcontrollers
Language	English