In Rn, n is 0..7. One of the four Register Banks is used
(selected by RS0 and RS1 in PSW)
PSW, #00011000B; Select
Register Bank 3
A, R7; Add the contents of
Register 7 to the Acc.
In Ri, i is 0 or 1.
There are 4
banks of working registers, but only one is active at a time. A hardware
reset enables bank 0, but a different bank is selected by modifying PSW bits
4 and 3 accordingly. E.g., MOV PSW, #00011000B activates register bank 3.