Question

Write a single 16-bit LC-3 instruction (in binary) that clears all the bits of R6 except the least significant two bits. In other words, after your instruction executes, bits 0 and 1 of R6 will be unchanged, and the rest of R6 will be zero.

Answer 1

Answer:

AND R6, R6, 0003.

Explanation:

Let's say we're taking the 0003 in decimal Hexa form.  

Which is to say, 0003 = 0000 0000 0000 0011.  

The AND operation can be performed between 0003 Hex number and R6, giving the last 2 bit the same as in R6 and leaving all bits as ' 0 ' in R6.  

Answer is: AND R6, R6, 0003.