In the manual it is written (page 28): "... When CSB is tied high, SPI functions are placed in high impedance mode. This mode turns on any SPI pin secondary functions." For example the output will be: DFS high = twos complement output or DFS low = offset binary output.
What happens if I use the serial configuration and program the register [0x14 Output mode] as 10 = gray code. When the CSB becomes inactive because I have finished programming the registers, does the register configuration or the pin configuration remain valid? In this second case I will never be able to have the gray code output. This is just an example to indicate that I don't understand how to activate serial mode without ever using the external pins. Last but not least, the fact that the SDIO and SCLK pins are valid as a second function, when CSB is off, forces me to provide specific electronics to bind these signals. Can I hypothesize that when I activated the serial mode (by writing a register) the second function of the pins becomes indifferent?