ADD Instruction Property 2

If an ADD instruction is executed, then only memory cell #dst is affected, since that is where the result of the opration is stored. All other memory cell values remain unchanged. More formally:

if the following are true:

  • instruction #i is add dst=d src1=s1 src2=s2
  • the PC at time t = i
  • not (other = d)

then value of cell other at time (t + 1) = value of cell other at time t

Let's take a look at the following computer:

Instructions
Memory Cells
Program Counter Time
0 0
LW Computer Simulator

Notice that only memory cell #2 is changed. Memory cells #0 and #1 remain the same. In other words:

if the following are true:

  • instruction #0 is addi dst=2 src=1 imm=5
  • the PC at time 0 = 0
  • not (1 = 2)

then value of cell 1 at time (0 + 1) = value of cell 1 at time 0


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