control register 2
| RXDMAEN | Rx buffer DMA enable  |  
| TXDMAEN | Tx buffer DMA enable  |  
| SSOE | SS output enable  |  
| NSSP | NSS pulse management  |  
| FRF | Frame format  |  
| ERRIE | Error interrupt enable  |  
| RXNEIE | RX buffer not empty interrupt enable  |  
| TXEIE | Tx buffer empty interrupt enable  |  
| DS | Data size  |  
| FRXTH | FIFO reception threshold  |  
| LDMA_RX | Last DMA transfer for reception  |  
| LDMA_TX | Last DMA transfer for transmission  |