ADD Instruction Property

The Add (ADD) instruction contains the following information:

  • source one (src1) - Memory cell number of the first operand.
  • source two (src2) - Memory cell number of the second operand
  • destination (dst) - Memory cell number where the sum will be stored.
If the current instruction is an ADD instruction, then the values in memory cell #src1 and memory cell #src2 will be summed and stored in dst. More fomally:

if the following are true:

  • instruction #i is add dst=d src1=s1 src2=s2
  • the PC at time t = i

then value of cell d at time (t + 1) = (value of cell s1 at time t) + (value of cell s2 at time t)

Here is an example of a simulator that contains an ADD instruction:
Instructions
Memory Cells
Program Counter Time
0 0
LW Computer Simulator

PC is 0, so the simulator is going to execute instruction #0. The src1 is 1 and src2 is 2. Thus, the operation is

value at memory cell #1 + memory cell #2

= 2 + 6

= 8

dst is 3, which means the result will be stored in memory cell #2.

This behavior can be expressed as follows:

if the following are true:

  • instruction #0 is add dst=3 src1=1 src2=2
  • the PC at time 0 = 0

then value of cell 3 at time (0 + 1) = (value of cell 1 at time 0) + (value of cell 2 at time 0)


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