First few steps in assembly code.

As I was playing with MED9.1 File, I was wondering how the function is called to load the value of a ROM address in my register

say the value of address 0x045678 is F6

how can I put this value, F6 , into register r12 for example.

With a variable it would look like lhz, r12, byte_45678

No idea how it works with a random ROM address.

Thanks for helping

Use next instructions:
1.Load Byte and Zero
lbz rD,d(rA) The EA is the sum (rA|0) + d. The byte in memory addressed by the EA is loaded into the low-order eight bits of rD. The remaining bits in rD are cleared.
2.Load Byte and Zero Indexed
lbzx rD,rA,rB The EA is the sum (rA|0) + (rB). The byte in memory addressed by the EA is loaded into the low-order eight bits of rD. The remaining bits in rD are cleared.
3.Load Byte and Zero with Update
lbzu rD,d(rA) The EA is the sum (rA) + d. The byte in memory addressed by the EA is loaded into the low-order eight bits of rD. The remaining bits in rD are cleared. The EA is placed into rA.
4.Load Byte and Zero with Update Indexed
lbzux rD,rA,rB The EA is the sum (rA) + (rB). The byte in memory addressed by the EA is loaded into the low-order eight bits of rD. The remaining bits in rD are cleared. The EA is placed into rA.