The register is represented by `A`, which is still 8 bits. I have not changed it. Only `B` is changed from 9 bits to 8 bits. and `C` is changed from 9 bits to 8 bits.
RK(B) encodes either register or constant (256 registers and 256 constants, 9 bits in total)
If your B is 8 bits then only 128 registers are addressable?
