Master:       send command         send dummy byte
                V                   V
       MOSI:  ___X  command    X_____X   dummy     X____
       MISO:                      ___X  command    X__
       SCK :  ___|_|_|_|_|_|_|_|_____|_|_|_|_|_|_|_|_____
                                V         ^
Slave :                      interrupt    |send answer
                                |<------->|
                                  command handling