8.1. Fetch Stage

So, in this fetch stage so, PC is equal to you are keeping the value of the memory address register can I actually merge this 2 in a single time step not possible, because in the first unit the value of the program counter will go to the memory address register.

In the Fetch Stage, the Program Counter (PC) indicates which instruction in memory should be fetched next. The PC's value is first sent to the Memory Address Register (MAR). It's important to note that this action requires a certain amount of time. Therefore, merging the activities of the PC and MAR into a single step isn’t feasible as each step needs to be completed before the next begins.

Think of the PC as a librarian who has to fetch a book (the instruction). The librarian needs to read which book (the address) to retrieve first before going to the shelves. There’s a clear line of action: first, identify the book by its address (putting its location in the MAR), and only then can the librarian go get it, showing the sequential nature of the fetch process.

So, if you look at it I am giving some because this job is over, you have told me what is the address. Now I go and bring the data from that memory location already you have given me from where I have to fetch the data. Then the job of the program counter is over, because program counter is telling me the address from where I have to give from the get the data from.

Once the PC has successfully given the address to the MAR, its job is done for that instruction fetch. The MAR will be responsible for retrieving the data from memory by reading the address already provided. At this point, since the PC is free to increment itself to point to the next instruction, it can now proceed to update its value.

Imagine the librarian finishing fetching one book and realizing they can now jot down the next book they need to retrieve while the current book is being checked out by the reader. This illustrates how tasks can be sequential but also how one process can overlap with another when there is no conflict.

So, if you are free at hand then actually I can reuse the PC that indicates I am incrementing it by one. So, memory, taking the data from the memory to the memory buffer register and program counter increment these 2 micro instructions you can do it in time steps 2.

During the second unit of time, while the MAR retrieves data, the program counter can be incremented. This merging of operations is efficient because it utilizes the available time effectively without stepping on any operational dependencies. The memory operations do not depend on the program counter's status, allowing both to happen simultaneously.

If our librarian now has a moment where they're waiting for the checkout process to complete, they can instantly pen the title of the next book they need to retrieve without interrupting the current process, saving time and ensuring an efficient flow.

So what is clock grouping proper sequence should be maintained you cannot alter the sequence that is I am getting the data; before I put the registers in address that cannot be done.

Clock grouping is a method ensuring that the sequence of microinstructions is maintained without conflicts. It means that certain steps must be executed in a predefined order to ensure that data is correctly fetched and stored. If, for example, one attempts to read and write to a register at the same time, it could lead to errors and incorrect data being used.

Think of it like following a recipe: you can’t go ahead and bake a cake before making the batter. Each step must be followed in sequence to ensure the result is successful—if you alter the order, the cake likely won't turn out right, just like computer operations can fail when steps are mishandled.

So, what I was telling you is that we are writing in the slide that what are the dependent dependency like for example memory, memory, memory to memory buffer register and instruction register to the memory.

The fetch stage culminates in understanding the dependencies that exist between different stages of instruction processing. Recognizing these dependencies is critical for creating effective communication and operations among the various registers at play. For instance, the data must first transfer from the memory to the Memory Buffer Register (MBR) before it can be moved to the Instruction Register (IR).

Imagine a conveyor belt in a factory where certain components can only move to the next station after they're ready. If a part needed for assembly isn't processed yet, it can’t be moved to the assembly line. This sequential dependency ensures everything fits together properly, just like the fetch stage must respect the data flow between registers.

--