STM8S datasheet(331/467 Pages) STMICROELECTRONICS

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RM0016

Universal asynchronous receiver transmitter (UART)

377

Break character

Setting the SBK bit transmits a break character. The break frame length depends on the M

bit (see Figure 114).

If the SBK bit is set to ‘1’ a break character is sent on the UART_TX line after completing the

current character transmission. This bit is reset by hardware when the break character is

completed (during the stop bit of the break character).The UART inserts a logic 1 bit at the

end of the last break frame to guarantee the recognition of the start bit of the next frame.

Note:

The break character is sent without taking into account the number of stop bits. If the UART

is programmed with 2 stop bits, the TX line is pulled low until the end of the first stop bit only.

Then 2 logic 1 bits are inserted before the next character.

Note:

If the software resets the SBK bit before the start of break transmission, the break character

is not transmitted. For two consecutive breaks, the SBK bit should be set after the stop bit of

the previous break.

Idle character

Setting the TEN bit drives the UART to send an idle frame before the first data frame.

22.3.3

Receiver

The UART can receive data words of either 8 or 9 bits. When the M bit is set, word length is

9 bits and the MSB is stored in the R8 bit in the UART_CR1 register.

Start bit detection

In the UART, the start bit is detected when a specific sequence of samples is recognized.

This sequence is: 1 1 1 0 X 0 X 0X 0X 0 X 0X 0. The start bit detection sequence shown in

Figure 117.

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