11.2.2. Read and Write Operations

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 learn how the Memory Data Register (MDR) is used to read data into Register R1. The process begins when the system acknowledges that the read operation is complete, indicated by the MFC (Memory Function Completed) signal turning to 1. Once this happens, the MDR outputs its stored value to the bus, allowing it to be transferred to R1. This operation effectively signifies the completion of the MOV instruction, which means moving data from memory to a register.

Think of it like a librarian handing over a book to a student. Before the book can be handed over (action completed, represented by the MFC signal), the librarian makes sure the student is ready to receive it (MDR out = 1). After the transfer, the student now has the book (data in R1), completing the borrowing process.

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; one was the read operation, next was the right operation very simple. Of course, first the value of 𝑅1 has to be written to 32. So, the register value 𝑅 instruction register has to be made 1, out because the default idea is that whatever instruction is there will be first in the instruction register. So, therefore, any instruction in a general thumb rule, what is there you have to first make the instruction register out that means, the value of the instruction register have to go to the memory address register.

This chunk describes the write operation where the value from Register R1 is stored in memory location identified by 32. The first step involves setting the instruction register to output (1 out), which allows the current instruction to be transferred to the Memory Address Register (MAR). This step is crucial because it defines the memory address where the data from R1 will be written.

Imagine writing a new address on a package before sending it out. First, you write down the address (outputting the instruction to the Memory Address Register). Then, once the address is set, you can hand over the package (the data from R1) to the postal service to be delivered to that address (the specified memory location).

Now, in this case, what happens, 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. In this case it will be just the reverse compared to the previous analysis. So, 𝑀𝐷𝑅 will be actually equal to in. So, now, the memory data register will be in a read mode because it will read something from the register 𝑅1 and that has to be dumped to the memory.

In this part of the chunk, we see the actual transfer of data from Register R1 to the memory via the Memory Data Register (MDR). The MDR switches to input mode to receive the value from R1. This is essentially the opposite of the previous read operation; now, we are storing data instead of retrieving it. The data from R1 is loaded into the MDR before being written to the specified memory address.

Consider this like packing a box after writing down the delivery address. You're filling the box (the MDR receiving data from R1) with items to send (the data being written to memory), and then you'll hand it over to the delivery service (the memory being updated with new data).

At this clock edge, the data of 𝑅1 has been moved to the memory data register write signal has been made one. So, now, the memory data register is going to write to the memory. So, I am making the memory data register from input mode to output mode which I am making it 1.

Here, we focus on the clock signal's role in synchronizing the write operation. Once the data is loaded into the MDR, the write signal is activated, prompting the MDR to transition to output mode. At this moment, the data within the MDR is ready to be sent to memory, thereby completing the memory write operation.

Imagine the moment just before a button is pressed to send a package off. The button press represents the activation of the write signal, transforming the prepared package (data in MDR) into a shipment ready to leave for its final destination (memory).

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