STM8S datasheet(338/467 Pages) STMICROELECTRONICS

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Universal asynchronous receiver transmitter (UART)

RM0016

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DocID14587 Rev 14

Table 56. UART receiver’s tolerance when UART_DIV[3:0] is different from zero

Note:

The values specified in Table 55 and Table 56 may slightly differ in the special case when

the received frames contain some Idle frames of exactly 10-bit times when M=0 (11-bit times

when M=1).

22.3.6

Parity control

Parity control (generation of parity bit in transmission and parity checking in reception) can

be enabled by setting the PCEN bit in the UART_CR1 register. Depending on the frame

length defined by the M bit, the possible UART frame formats are as listed in Table 57.

Legends: SB: Start Bit, STB: Stop Bit, PB: Parity Bit

Note:

In case of wakeup by an address mark, the MSB bit of the data is taken into account and not

the parity bit

Even parity: the parity bit is calculated to obtain an even number of “1s” inside the frame

made of the 7 or 8 LSB bits (depending on whether M is equal to 0 or 1) and the parity bit.

Ex: data=00110101; 4 bits set => parity bit will be 0 if even parity is selected (PS bit in

UART_CR1 = 0).

Odd parity: the parity bit is calculated to obtain an odd number of “1s” inside the frame

made of the 7 or 8 LSB bits (depending on whether M is equal to 0 or 1) and the parity bit.

Example: data=00110101; 4 bits set => parity bit will be 1 if odd parity is selected (PS bit in

UART_CR1 = 1).

Transmission: If the PCEN bit is set in UART_CR1 then the MSB bit of the data written in

the data register is not transmitted but is changed by the parity bit to give an even number of

‘1’s if even parity is selected (PS=0) or an odd number of ‘1’s if odd parity is selected

(PS=1).

Reception: If the parity check fails, the PE flag is set in the UART_SR register and an

interrupt is generated if the PIEN bit is set in the UART_CR1 register.

M bit

NF is an error

NF is don’t care

3.33%

3.88%

3.03%

3.53%

Table 57. Frame format

M bit

PCEN bit

UART frame

| SB | 8 bit data | STB |

| SB | 7-bit data | PB | STB |

| SB | 9-bit data | STB |

| SB | 8-bit data PB | STB |

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