11.2. Store Instruction

Now, what you will do now we have to read of memory data register to the register 𝑅1 that is you have to do this part that memory data register value will has to be dumped to register 𝑅1. So, only after that 𝑀𝐹𝐶 signal has become 1, you can make the memory data register signal as out. Because before that if you see the memory data signal was a 1 over here in one that is memory data register in was a 1 that means it was reading from the memory. This 𝑀𝐹𝐶 signal is saying that the reading is over. So, now, you make 𝑀𝐷𝑅_𝑜𝑢𝑡 = 1 that means now it will dump the value whatever was in the memory data register which is taken from the memory to the bus. And then 𝑅 = 1 that means, whatever was in the memory data register will dump to the register 𝑅1 and this instruction of 𝑀𝑂𝑉 𝑅1, 32 will be over.

In this chunk, we discuss how the value stored in the Memory Data Register (MDR) is transferred to a specific register, R1. The process is initiated once the Memory Function Control (MFC) signal indicates that the reading operation from memory is complete. When MFC is set to 1, the output signal of the MDR can also be enabled (MDR_out = 1). This allows the value contained within the MDR to be transferred to the appropriate register, in this case, R1. The instruction MOV R1, 32 signifies that the data from memory location 32 is now stored in register R1, concluding this transfer process.

Imagine you’ve just received an important parcel (the data from memory) from a delivery service (the memory). You can only open the parcel once the delivery service confirms it has been successfully delivered (indicating the MFC signal is set to 1). Once you open the parcel (MDR becomes active), you carefully take out the contents (the data in the MDR) and place them in your drawer (register R1). Now that the contents are in your drawer, you can use them whenever you need.

Now, let us say that there is a store instruction move means what we have done, we have taken the value of memory location 32 whatever was there, we have moved to 𝑅1. Now, let us very quickly see that if this is the reverse one that is if there is something in memory register 𝑅1, sorry if there is some value in 𝑅1, we want to dump it to memory looking at 32.

This chunk introduces the scenario where the process is reversed; instead of fetching data from memory, we need to store data back into memory. If a value already exists in register R1, the task is to send this value to the memory location specified, which is 32 in this case. The instruction execution begins by setting the output operation for the instruction register so that the memory address can be accessed. This operation ensures that the instruction register's value indicating the desired memory location is transferred to the Memory Address Register (MAR), readying the system to write the value from R1 to the specified memory address.

Think of this as putting a document into a filing cabinet (memory). First, you need to check which folder you need to place your document in (determining the memory address from the instruction register). Once you know the correct folder (memory location 32), you can then take your document from your desk (the value in R1) and store it in that specific folder. The instruction register acts like a label telling you which folder to use.

Now, in this case, you have to write; in the previous case what happened it was a read now it is basically a write; that means, whatever is in the register 𝑅1 has to go to the memory.

Here, we focus on how the system prepares for a write operation to memory. Unlike the read operation, where data is fetched from memory to the register, this write operation requires the data that exists in register R1 to be sent to the memory. The Memory Data Register (MDR) must be set to receive the output data, which means the data from R1 is pushed into the MDR, effectively staging it before it's sent out to memory. This transition into a write state allows the value to be stored correctly at the specified memory location.

Consider this step as preparing to replace an old document in a filing cabinet with a new one. You take the new document (the data in R1) and position it in your hands, ready to place it into the cabinet (the memory). You can’t just throw it in; you must ensure that the old document is removed and the new one is positioned correctly.

So, in case what happens in the second case, so this is your register memory data register, which is in mode, and your register 𝑅1 is in the out mode. So, the register will dump the value which will go to the memory data register.

This part of the process describes the final execution of the write operation. As the memory data register is set to output mode, the data from R1 is transferred to the memory data register, effectively moving the data into the pipeline where it can be sent to memory. After the data transfer, it is essential to enable the write command, indicating that the system is ready to save this data into the designated location in memory. Control signals manage this process, ensuring the correct timing and sequence to avoid data conflicts.

Imagine you have physically placed the new document into the filing cabinet—the action of writing is complete. Now you need to make sure the filing cabinet is securely closed (sending the write command) so that the new document is officially stored and won’t be lost or confused with other documents. It’s crucial that the cabinet (memory) knows it’s supposed to accept the new document (data) at that specific location.

Now, what happens so now your memory data register already has the value, which is in the register. This phase is over. So, last microinstruction basically it will let us see what it will do this is your instruction.

In this concluding phase of the write operation, the memory data register will hold the value ready to write. The control signals must ensure that the memory is notified of the new incoming data and that the write command has been issued. Once the operations have been completed and the control signal indicates that the write operation was successful, the memory data register is cleared, freeing it up for future operations.

This last step can be likened to sealing the filing cabinet and filing the paperwork away for safekeeping. Once the cabinet is closed and locked (the memory data register is cleared), you can now move on to your next task without worrying about the documents you just saved.

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