12.1.4. Interfacing Registers: MAR and MBR

Now, basically what we are going to do in a fetch cycle. So, it is a fetching and information from memory to the processor.

The fetch cycle is a critical process that involves retrieving data or instructions from memory and sending it to the processor for execution. It is the first step in processing information in a computer system, where the program counter (PC) holds the address of the next instruction to be fetched.

Think of it like going to a library to retrieve a book. You need to know the exact location (address) of the book before you can fetch it. In computing, the program counter works like the librarian, guiding you to the right shelf.

We are having a special purpose register are called program counter, 𝑃𝐶 - program counter. So, in that particular case, what will happen I am having a call register called program counter, and program counter will have the address of this particular memory location.

The program counter is a special register that stores the address of the next instruction to be executed. When the processor completes the execution of an instruction, it increments the PC to point to the subsequent instruction, ensuring that the operations are executed in order.

Imagine a road trip where you follow a map. The program counter is like the map, guiding you from one destination (instruction) to the next. You look at the map to find where to go next after reaching each stop.

After fetching one instruction then what will happen we have to after completion of this particular instruction, we have to fetch the instruction from next memory location.

Once an instruction is fetched, the processor completes its execution. The PC then indicates the next memory address to fetch the following instruction. This continuous cycle of fetching, executing, and updating the PC ensures a smooth flow of operation, maintaining the sequence of execution.

Think of it like reading a book: once you finish a chapter (instruction), you naturally turn to the next chapter (next instruction) until you complete the book (program).

Now, we are having two special purpose register, one is known as 𝑀𝐴𝑅 - memory address register, and second one is your 𝑀𝐵𝑅 - memory buffer register.

The Memory Address Register (MAR) holds the address of the memory location from which data is to be fetched or to which data is to be written. The Memory Buffer Register (MBR), on the other hand, temporarily holds data that is being transferred to or from the memory. Together, they act as intermediaries between the processor and the memory, facilitating the data transfer process during operations.

Imagine you are sending a package. The MAR is like the label on the package that specifies the address where the package should go, while the MBR is the package itself—it contains the actual data (contents) to be sent or received.

First that address we have to put it into the 𝑀𝐴𝑅. After that this address will go to this particular memory unit through this system bus.

In the fetch cycle, the address stored in the program counter is moved to the MAR. The processor then sends a read signal to access the memory contents at this address. Once the data is retrieved, it is stored in the MBR, ready to be transferred to the instruction register (IR) for decoding and execution.

It's like ordering a pizza. You first give your address (MAR) to the pizza delivery service (memory). When the delivery person arrives (completes the read), they bring your pizza (data) to you (MBR), ready for you to enjoy.

Once we have the instruction in the instruction register, then processor will be knowing what operation we need to perform.

After the instruction is stored in the Instruction Register (IR), the processor decodes this instruction to determine the required operations. The Control Unit generates the necessary signals to execute the instruction, coordinating various components of the processor to carry out the task.

Think of a director (control unit) giving instructions to actors (processor components) after reading a script (instruction). The director knows exactly what scenes need to be shot (operations) and how to direct the actors to deliver the performance.

In write operation what happens we are going to write the information from a register to the memory.

In a write operation, first, the address where the data needs to be stored is placed in the MAR. Then, the data is moved to the MBR, and a write signal is sent to the memory, instructing it to store the data from the MBR at the specified address in the MAR.

Imagine you want to send a letter. You write the address on the envelope (MAR), place your letter inside (data in MBR), and then drop it in the mailbox to be delivered (write operation).

We should not read and write the same register at the same time, because if we are reading from some memory location or reading from a register, at the same time we should not write the same in same information to the register.

Conflict occurs when multiple operations are attempted simultaneously on the same resource, which can lead to errors. Certain operations must follow a strict sequence to avoid such conflicts. For example, the address must be set in the MAR before fetching data from that address into the MBR, ensuring that the processor operates efficiently and without errors.

It's similar to a traffic system: you can't have cars (data) traveling in both directions on the same road (register) at the same time. Just like traffic signals control the flow of vehicles, timing signals ensure that operations occur in a safe and orderly fashion.

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