Thank you sir . I think I am understanding. Your response
Shimon Schocken wrote
There is no such command M=16 in the Hack language.
got me thinking. So I went back to the book again.
The D=A is a "C-instruction", 0110000. I decoded the "comp" bits and found the ALU computation ends up outputting A (figure 4.3), which is 16.
The Destination bits are 010, which says that the ALU output will be fed into the D register (Figure 4.4).
Thanks again. I got the my Mult.asm successfully working.