13.1.3. Stage 3: Loading Instruction into Register

Let us again clean it up, because we will have to revisit this figure many times. So, again I am cleaning it up. So, next is what? Now what now actually next stage is till now we have seen, that the output of this $PC = PC + 1$ is memory is in register $IR$ and memory has you have given the command to read the memory.

In this section, we introduce the Instruction Register (IR) and its role in executing instructions. The IR stores the instruction fetched from memory that the CPU is currently processing. Before we can load a new instruction into the IR, we need to ensure that the previous instruction has been dealt with, and we clean up any previous references or figures in our understanding to avoid confusion as we move forward.

Think of the IR like a ticket in a ticket booth - it tells you what you are supposed to do next at the concert or movie. Just like you don't want to hold onto a previous ticket when you need to enter for a new show, the CPU needs to prepare the IR for the next instruction without the baggage of older instructions.

In the second stage what we do? so whatever I told you about the first one is written over here, you can read it now what is it says $Z$ out. So now, what out in this $IR$ has, if you look at the initial last slide then $IR$ had the value of $PC = PC + 1$, but at that time it was $Z$.

This chunk explains the importance of incrementing the Program Counter (PC). The PC keeps track of the next instruction to be executed. Every time an instruction is processed, the PC is incremented so it points to the subsequent instruction in memory, ensuring a linear flow of execution. The new value of the PC is then passed to the IR for processing.

Imagine a train traveling along a track. Each station it stops at represents an instruction. The train conductor (PC) marks each station visited and moves to the next station (increments) continuously. Once a station (instruction) is completed, the conductor quickly checks for the next stop (instruction) before continuing on their route.

Now, I am making as $Z$ and $PC$; that means, the value of $IR$ will go to $PC$ program counter, via the bus because $Z$ and $PC$ and we are waiting for $WFM$; that means, if the signal is one; that means, what the value of the memory location, where the instruction was there is loaded into the memory data register or the memory buffer register.

In this stage, the IR value is prepared to transfer to the PC via the bus. The system waits for the memory to indicate that it is ready to send the instruction. The control signal $WFM$ indicates whether the fetching operation is complete. This signaling ensures that data is only transferred when memory is prepared, preventing errors.

Consider a waiter in a restaurant who waits until the chef has finished preparing a dish before serving it to a customer. The waiter (like the bus) does not just rush in to take the dish. They want to make sure it's ready (the memory) so that the customer gets their meal at the right time, perfectly prepared.

After that what happens? Now the memory is ready, now what you have to do you have to load it into load it, load the value of this instruction into the instruction register, very simple you will make memory data register out and register in as simple as that just have a very quick look.

Once memory signals readiness, the instruction can be loaded into the IR. This process involves transferring data from the Memory Data Register (MDR) to the IR. This is an essential step for the CPU as it prepares to execute the command contained in the instruction.

Think about a librarian who gets a list of books to be checked out. When the list is ready (memory is ready), the librarian (CPU) simply moves the list (instruction) to the designated checking-out area (IR), allowing the checkout process (execution) to begin efficiently.

So, in the 2nd stage $PC$ , this data will be read from this memory this $IR$, which actually nothing but $PC = PC + 1$ and it will be read to the $PC$ by this bus.

In this step, the freshly loaded data in IR is accessed and the system prepares to execute it. The data, which is now in the IR, is considered ready for processing. The relevance of each component is brought back into focus, indicating how the prepared instruction transitions back to the PC for execution.

Imagine a teacher (the CPU) taking a student’s homework (the instruction from the IR) and preparing it for grading. The teacher needs to bring it back to the grading table (the PC) to deliver feedback, thus transforming the prepared work into a graded assignment.

--