Ok, so there are
two 16-bit registers and
eight 8-bit registers.
A, B, C, D, E, H, L & F.
Those eight 8-bit registers can
be combined
to make some 16-bit registers.
AF, BC, DE & HL.
Which means that one can
access register A from AF by
getting the last
8 bits of the AF register
that would be bits 15 to 7…
Sometimes an instruction may
need that.