14.5.1. Immediate Mode Example

The first instruction mode the simplest one is the immediate mode. So, we are just saying LOAD R1, 32; that means, the value of 32 constant will be loaded to R1 and we are assuming that this instruction takes a single word. So, in this case the PC has to be incremented by 1.

In assembly language, the immediate mode refers to a way of loading data directly into a register. For example, LOAD R1, 32 means that we want to load the value 32 into register R1. This instruction implies that the processor can directly use the number 32 without needing to find it in memory, which speeds up the operation since it reduces the number of steps required to execute.

Think of it like ordering a pizza. If you have your favorite pizza ready at home (like the value 32), you can quickly take it out and eat it (load it into R1). However, if you had to go to the store (memory) to buy a pizza each time you wanted to eat, it would take longer. Immediate mode allows you to skip that trip and access the pizza directly.

So, what are the steps? So, the first step if you look you know the program counter will be the output it will go to memory address in. So, what does it mean already we have discussed with the figure in the last class. So, this I am going to keep a bit brief. So, PC out and memory register addressing; that means, what the output of the program counter will be loaded to the memory address, will be in a read mode select will be 0; add and Z. So, up to this PC out, memory register address in and read this corresponds to the fetch part select zero; that means, you are going to add the constant to the program counter and in the output will be of the ALU will be going to register Z.

Executing an immediate mode instruction like LOAD R1, 32 involves several steps: First, the current value of the program counter (PC) is read, determining where in memory the instruction is located. This value is used to fetch the instruction from memory. After fetching the instruction, the constant value (in this case, 32) is directly loaded into the specified register (R1). The PC is then incremented to point to the next instruction.

Imagine you're reading a recipe book (the program). When you start at a specific page (the PC), you read the ingredients (the instruction). Once you note the required ingredients (like 32), you can just take them directly from your pantry (the register), and then you turn to the next page for the next step of the recipe.

In the second stage Z; that means, the output of the ALU that is Z which is now equal to PC = PC + constant will be going to PC; that means, the output that is PC = PC + constant will be noted into the PC via a bus and we are waiting till the memory sends the signal that I am ready.

In this step, after the instruction is fetched and executed, the next task is to update the program counter to point to the next instruction. This is done by taking the current PC value and adding a constant (which is generally 1, to move to the next instruction). The updated value is then stored back in the PC, ready for the next cycle.

Think of each recipe step as a series of instructions you need to follow. Once you finish one step (like loading 32 into R1), you turn the page to the next step (updating the PC). This keeps you organized and ensures you follow the recipe in the correct order.

Once it is ready the output of the memory data register, which now has the instruction that is equal to LOAD R1, 32 will be loaded into the instruction register.

After the system has signaled that it is ready, the instruction that has just been fetched (LOAD R1, 32) is transferred from the memory data register into the instruction register. This is where the CPU keeps the currently executing instruction, allowing it to decode and execute it.

Using the recipe analogy, this step is akin to noting down the specific action you need to take after you've understood what ingredients you need. Once you have everything ready (like the instruction being in the memory data register), you jot it down on a sticky note (the instruction register) to remind you of what to do next.

In the last stage we will have to take from the instruction register the value of 32 and dump it into register R1. So, it will give the value. So, there are basically 3 steps involved in this case extremely simple, that is fetch and after this just you require one stage in which case, the value of the instruction register immediate part will go over here.

The final step in executing an immediate mode instruction is to transfer the immediate value (in this case, 32) from the instruction register to the designated register (R1). This is performed through a simple bus transfer, completing the instruction execution.

This last step is like putting the ready pizza (the value 32) onto your plate (register R1) so that you can enjoy it. You've gathered everything you need, and now it's just about serving it to yourself for immediate use.

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