The sequence of Mic-1 instructions below realize a new instruction bish8pu x (x is an offset in 8 bit in binary code). What is the meaning of this set of instructions?
bish8pu2 H=TOS << 8
bish8pu3 TOS=MDR=MBRU OR H;wr
bish8pu5 goto Main1
Thanks a lot
Best How To :
The instruction shifts the value in the TOS register to the left by 8 and stores the result in the H register. It then bitwise ORs the value in the H register with the value of the instruction's immediate byte and stores the resulting value both in the TOS register and in the location in memory pointed to by the SP.
Basically it computes
[SP] = [SP] * 256 + immediate, where
[SP] is the memory location pointed to by the SP register. (That is, assuming that the TOS register caches the value pointed to by SP.).