Hi Roger,
I'm confused, where do you see that shifiting in three bytes like that should give you the three first byte of a cards S/N number?

It looks to me as if the RFID reader chip implements a "proper" SPI slave meaning you have to shift data out at the same time as you shift data in. If that's the case SHIFTIN/SHIFTOUT won't work because it can only shift data out OR shift data in, it can't do it simultanously.

/Henrik.