From note #13:

> The silicon implementation of the lower eight bits of the ALU / registers is flipped compared to the upper eight bits. The motivation is to put the ALU signals next to the flag circuitry that needs these signals.

This caught me out because I was expecting some more obvious rotation or discernible mirroring of the upper half and lower half. Is the layout of bits 15:8 entirely different yet logically equivalent? Looking closely though I do see some similarities in the outer circuits at the very top and very bottom, yet there is a large gap across the lower bank.