NEC uPD78P078 - Manual (Page 121)

121
CHAPTER 5 CPU ARCHITECTURE
5.3.4 Register addressing
[Function]
Register pair (AX) contents to be specified with an instruction word are transferred to the program counter (PC)
and branched.
This function is carried out when the BR AX instruction is executed.
[Illustration]
7 0
rp
0 7
A X
15 0
PC
8 7