Store Instruction Property

The store (STORE) instruction copies the value at memory cell #src to memory cell #destination, where destination is the value in memory cell #addr + imm. More formally:

A simple copy instruction would just copy the value in cell #src to cell #addr. But instead of using addr as the destination, this uses the value stored in cell #addr as the destination. You can also add a constant value to offset the destination address.

This is best illustrated by examples. Take a look at the following:

Initially, the PC is 0, so instruction #0 is executed. Instruction #0 is a STORE instruction. The source value is at memory cell #5, which is 9. Now let's look up the destination cell number. addr is 1, so look in cell #1, which is 3. Since imm is 0, it does not affect the destination. Thus, the destination cell number is 3 (not 1!).

Thus, computer will store 9 in memory cell #3. This example can be expressed as:

if the following are true:

• instruction #0 is store src=5 addr=1 imm=0
• the PC at time 0 = 0

then value of cell ((value of cell 1 at time 0) + 0) at time (0 + 1) = value of cell 5 at time 0

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