(1) Can data be received while a transmit is being performed?
(2) Is the shift register the same for both transmit and receive?
(1) Yes, data can be received while a transmit is being performed.
(2) There are separate circuits for the transmit and receive shift registers. Although the addresses in memory are the same, they each have their own buffer shift register. Accordingly, the transmit buffer register is accessed during a write and the receive buffer register is accessed during a read.