Table 196. Frame Formats; Usart Parity Control - ST STM32L4x6 Reference Manual

RM0351
36.5.9

USART parity control

Parity control (generation of parity bit in transmission and parity checking in reception) can
be enabled by setting the PCE bit in the USARTx_CR1 register. Depending on the frame
length defined by the M bits, the possible USART frame formats are as listed in
M bits
00
00
01
01
10
10
1. Legends: SB: start bit, STB: stop bit, PB: parity bit. In the data register, the PB is always taking the MSB
position (9th, 8th or 7th, depending on the M bits value).
Even parity
The parity bit is calculated to obtain an even number of "1s" inside the frame of the 6, 7 or 8
LSB bits (depending on M bits values) and the parity bit.
As an example, if data=00110101, and 4 bits are set, then the parity bit will be 0 if even
parity is selected (PS bit in USARTx_CR1 = 0).
Odd parity
The parity bit is calculated to obtain an odd number of "1s" inside the frame made of the 6, 7
or 8 LSB bits (depending on M bits values) and the parity bit.
As an example, if data=00110101 and 4 bits set, then the parity bit will be 1 if odd parity is
selected (PS bit in USARTx_CR1 = 1).
Parity checking in reception
If the parity check fails, the PE flag is set in the USARTx_ISR register and an interrupt is
generated if PEIE is set in the USARTx_CR1 register. The PE flag is cleared by software
writing 1 to the PECF in the USARTx_ICR register.
Parity generation in transmission
If the PCE bit is set in USARTx_CR1, then the MSB bit of the data written in the data
register is transmitted but is changed by the parity bit (even number of "1s" if even parity is
selected (PS=0) or an odd number of "1s" if odd parity is selected (PS=1)).
Universal synchronous asynchronous receiver transmitter (USART)

Table 196. Frame formats

PCE bit
0
1
0
1
0
1
DocID024597 Rev 3
(1)
USART frame
| SB | 8-bit data | STB |
| SB | 7-bit data | PB | STB |
| SB | 9-bit data | STB |
| SB | 8-bit data | PB | STB |
| SB | 7-bit data | STB |
| SB | 6-bit data | PB | STB |
Table 196.
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