13.3.3. Designing Control Steps for Different Instructions

Let us again clean it up, because we will have to revisit this figure many times. So, again I am cleaning it up.

This opening statement highlights the importance of organizing the information clearly. The author suggests that there will be multiple references to a figure throughout the discussion, indicating that understanding the visual representation will be essential as the section progresses.

Think of this as preparing a roadmap for a long journey. Before you start, you want to ensure your map is clear and easy to understand, because you'll refer to it many times during your travels.

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 second stage what we do?

In this first stage of executing an instruction, the program counter (PC) is incremented by 1. This means the CPU is preparing to fetch the next instruction from memory. The result of this increment is stored in the Instruction Register (IR), which temporarily holds the command for processing.

Imagine you're reading a book. Every time you finish a page, you naturally turn to the next one. The program counter acts like your finger guiding you to the next page, ensuring you're always prepared for what comes next.

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.

The next step involves moving the instruction stored in the Instruction Register to the Program Counter. This transition is crucial when transitioning from processing one instruction to preparing for the next. The output data helps maintain a sequence in the instruction cycle.

Imagine a relay race, where a runner passes a baton to the next runner. In computing, this passing of instructions from one register to another ensures that the race (or operation) continues without interruption.

We are waiting for WFM command, so waiting till the memory out in says that, I am ready and whatever you asked in the first stage it has been dumped to the memory buffer register.

This step emphasizes the synchronization needed between the CPU and memory. The CPU does not proceed until it receives confirmation from memory that it is ready to provide the data stored in the memory buffer register.

Consider a waiter in a restaurant. The kitchen (memory) needs to confirm that a dish is ready before the waiter (CPU) can serve it to the customer. This ensures that no one receives an incomplete order.

Now what happens? Now the memory is ready, now what you have to do you have to load it into the instruction register, very simple you will make memory data register out and register in.

Once the memory confirms readiness, the CPU moves to load the instruction from the memory data register into the instruction register. This process involves shifting the contents of the memory data register out and effectively placing them into the instruction register.

Think of it as transferring a finished drawing from the drafting table (memory data register) to a display board (instruction register) where it can be viewed and used.

So now, your instruction is over here, you have to load it to the instruction register.

Once the instruction is loaded into the instruction register, the CPU is now configured to execute this command. This step is vital because it determines the actions that the CPU will take next based on the instruction retrieved.

This can be likened to an employee receiving a task directive. Once the task is read and understood, the employee is ready to proceed with accomplishing the objective.

So now what? So, you have to take this value M and loaded it into the memory address register.

In this step, the CPU needs to prepare for the operation by loading the memory address from where it needs to retrieve data. This action involves taking the operand from the instruction that indicates memory and placing it into the memory address register for further processing.

Imagine you need a specific book from a library; first, you must identify its location. This action of storing the book's location into your mental 'address register' prepares you for the next step of retrieving it.

Now, once the memory says that I am done with it, the data this M data is now loaded in the memory data register.

Following the retrieval of the address, once the memory has completed reading and signifies readiness, the data can now be transferred from the memory data register to the target register (like R1). This is crucial as it completes the instruction cycle and allows the CPU to perform the actual computation or data handling.

This final step can be compared to receiving the book you ordered from the librarian. Once you have it, you can read it and make notes on your paper – akin to performing operations on data.

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