STM8S datasheet(335/467 Pages) STMICROELECTRONICS

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RM0016

Universal asynchronous receiver transmitter (UART)

377

When noise is detected in a frame:

•

The NF is set at the rising edge of the RXNE bit.

•

The invalid data is transferred from the Shift register to the UART_DR register.

This bit rises at the same time as the RXNE bit which generates an interrupt. The NF bit is

reset by a UART_SR register read operation followed by a UART_DR register read

operation.

Framing error

A framing error is detected when:

The stop bit is not recognized on reception at the expected time, following either a de-

synchronization or excessive noise.

When the framing error is detected:

•

The FE bit is set by hardware

•

The invalid data is transferred from the Shift register to the UART_DR register.

•

No interrupt is generated in case of single byte communication. However, this bit rises

at the same time as the RXNE bit which itself generates an interrupt.

The FE bit is reset by a UART_SR register read operation followed by a UART_DR register

read operation.

Configurable stop bits during reception:

The number of stop bits to be received can be configured through the control bits of Control

mode.

1 Stop Bit: Sampling for 1 stop Bit is done on the 8th, 9th and 10th samples.

1.5 Stop Bits (Smartcard mode only): Sampling for 1.5 stop bits is done on the

16th,17th and 18th samples. An NACK signal received from the Smartcard forces the

data signal low during the sampling, flagged as a framing error. Then, the FE flag is set

with the RXNE at the end of the 1.5 stop bit.

2 Stop Bits: Sampling for 2 stop bits is done on the 8th, 9th and 10th samples of the first

stop bit.If a framing error is detected during the first stop bit the framing error flag will be

set. The second stop bit is not checked for framing error. The RXNE flag will be set at

the end of the first stop bit.

Table 53. Noise detection from sampled data

Sampled value

NF status

Received bit value

Data validity

000

Valid

001

Not Valid

010

Not Valid

011

Not Valid

100

Not Valid

101

Not Valid

110

Not Valid

111

Valid

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