SPI2_CR1 register
| CPHA | Clock phase 
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| CPOL | Clock polarity 
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| MSTR | Master selection 
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| BR | Baud rate control 
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| SPE | SPI enable 
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| LSBFIRST | Frame format 
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| SSI | Internal slave select This bit has an effect only when the SSM bit is set. The value of this bit is forced onto the NSS pin and the I/O value of the NSS pin is ignored.  |  
| SSM | Software slave management When the SSM bit is set, the NSS pin input is replaced with the value from the SSI bit. 
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| RXONLY | Receive only mode enabled. This bit enables simplex communication using a single unidirectional line to receive data exclusively. Keep BIDIMODE bit clear when receive only mode is active.This bit is also useful in a multislave system in which this particular slave is not accessed, the output from the accessed slave is not corrupted. 
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| CRCL | CRC length This bit is set and cleared by software to select the CRC length. 
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| CRCNEXT | Transmit CRC next 
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| CRCEN | Hardware CRC calculation enable 
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| BIDIOE | Output enable in bidirectional mode This bit combined with the BIDIMODE bit selects the direction of transfer in bidirectional mode 
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| BIDIMODE | Bidirectional data mode enable. This bit enables half-duplex communication using common single bidirectional data line. Keep RXONLY bit clear when bidirectional mode is active. 
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