AD5543: Behaviour on signals shorter than 16bit

Hello engineers!

I'm planning to use the D/A converter AD5543/5553 to convert a 16bit position
signal. In addition to this, I also want to send a 8bit signal to the uC on the
same interface but the D/A should not react to this signals. Therefore I need to know how the D/A converter behaves when the
chip select is not 16bit but 8bit long. Is the data then "thrown away"?

Thanks in advance for your help.
Best regards