STM8S datasheet(276/467 Pages) STMICROELECTRONICS

276 / 467 page

Serial peripheral interface (SPI)

RM0016

276/467

DocID14587 Rev 14

SPI communication using CRC is possible through the following procedure:

•

Program the CPOL, CPHA, LSBfirst, BR, SSM, SSI and MSTR values.

•

Program the polynomial in the SPI_CRCPR register

•

Enable the CRC calculation by setting the CRCEN bit in the SPI_CR1 register. This

also clears the SPI_RXCRCR and SPI_TXCRCR registers

•

Enable the SPI by setting the SPE bit in SPI_CR1

•

Start the communication and sustain the communication until all but one byte has been

transmitted or received.

•

On writing the last byte to the Txbuffer, set the CRCNext bit in the SPI_CR2 register to

indicate that after transmission of the last byte, the CRC should be transmitted. The

CRC calculation will be frozen during the CRC transmission.

•

After transmitting the last byte, the SPI transmits the CRC. CRCNext bit is reset. The

CRC is also received and compared against the SPI_RXCRCR value. If the value does

not match, the CRCERR flag in SPI_SR is set and an interrupt can be generated when

the ERRIE in the SPI_ICR register is set.

Note:

With high bit rate frequencies, the user must take care when transmitting CRC. As the

number of used CPU cycles has to be as low as possible in the CRC transfer phase, the

calling of software functions in the CRC transmission sequence is forbidden to avoid errors

in the last data and CRC reception.

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