Low-power universal asynchronous receiver transmitter (LPUART) RM0440
1694/2126 RM0440 Rev 4
multibuffer communication, an interrupt is issued if the EIE bit is set in the
LPUART_CR3 register.
The FE bit is reset by writing 1 to the FECF in the LPUART_ICR register.
Configurable stop bits during reception
The number of stop bits to be received can be configured through the control bits of
LPUART_CR2: it can be either 1 or 2 in normal mode.
• 1 stop bit: sampling for 1 stop bit is done on the 8th, 9th and 10th samples.
• 2 stop bits: sampling for the 2 stop bits is done in the middle of the second stop bit.
The RXNE and FE flags are set just after this sample i.e. during the second stop bit.
The first stop bit is not checked for framing error.
38.4.7 LPUART baud rate generation
The baud rate for the receiver and transmitter (Rx and Tx) are both set to the value
programmed in the LPUART_BRR register.
LPUARTDIV is defined in the LPUART_BRR register.
Note: The baud counters are updated to the new value in the baud registers after a write operation
to LPUART_BRR. Hence the baud rate register value should not be changed during
communication.
It is forbidden to write values lower than 0x300 in the LPUART_BRR register.
f
CK
must range from 3 x baud rate to 4096 x baud rate.
The maximum baud rate that can be reached when the LPUART clock source is the LSE, is
9600 baud. Higher baud rates can be reached when the LPUART is clocked by clock
sources different from the LSE clock. For example, if the LPUART clock source frequency is
100 MHz, the maximum baud rate that can be reached is about 33 Mbaud.
Tx/Rx baud
256 lpuart× ckpres
LPUARTDIV
----------------------------------------------------
=
Table 351. Error calculation for programmed baud rates at lpuart_ker_ck_pres= 32,768 KHz
Baud rate lpuart_ker_ck_pres= 32,768 KHz
S.No Desired Actual
Value programmed in the baud
rate register
% Error = (Calculated - Desired)
B.rate / Desired B.rate
1 0.3 KBps 0.3 KBps 0x6D3A 0
2 0.6 KBps 0.6 KBps 0x369D 0
3 1200 Bps 1200.087 Bps 0x1B4E 0.007
4 2400 Bps 2400.17 Bps 0xDA7 0.007
5 4800 Bps 4801.72 Bps 0x6D3 0.035
6 9600 KBps 9608.94 Bps 0x369 0.093
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