11.2.3. Microinstruction Sequence

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.

This chunk describes the process of transferring data from the memory data register (MDR) to register R1. The sequence starts with determining when to perform the transfer, signaled by the MFC (Memory Function Completed) signal. Once this signal indicates that reading is complete (MFC becomes 1), the control unit sets MDR_out to 1. This command allows the contents of the MDR, which has just read from memory, to be sent to the bus and subsequently transferred to R1. The operation MOV R1, 32 thus concludes when R1 is filled with the value from the MDR.

Think of the MDR as a temporary container that holds ingredients (data from memory). The MFC signal acts like a timer that alerts the chef (control unit) when the ingredients are ready to be transferred. Once alerted, the chef lifts the lid on the container (sets MDR_out to 1) and pours the ingredients directly into a bowl (register R1), completing the preparation of a dish (the instruction MOV R1, 32).

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 write 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 focuses on the opposite operation, where the value stored in R1 is written to a specific memory address (32). The first step is to set the output of the instruction register (IR_out) to 1 so the instruction stored in the IR can be sent to the memory address register (MAR). This step is crucial as it prepares the system to know where to write the value, which is specified by the instruction. Hence, the operation switches from reading from memory to writing to memory.

Imagine writing a message (value in R1) on a piece of paper (memory location 32). Before you can write the message, you need to know where your paper is (set instruction register output). In this analogy, opening the drawer to take out the paper represents setting the instruction register output to tell the system where to write the message.

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. So, now in this case this is the memory, this is the 32 memory location has to be read and in fact, there is a memory data register. So, in the read mode from the memory, the memory register is to be read, but is the write operation, so you have to dump the value over here.

This chunk explains the actual writing of data. In contrast to reading, where data is fetched from memory, a write operation involves taking the data from R1 and sending it to the memory at the specified address (32). The memory data register (MDR) will temporarily hold this value during the transfer process. It is important to note that the system switches from a read mode to a write mode, adjusting its operations accordingly.

Consider the process like sending a letter. When sending a letter, you take your message (data in R1), put it into an envelope (MDR), and then once you address the envelope (point out where to send it, which is the memory address 32), you can drop it into the mailbox (write operation to memory). This step is essential for ensuring the letter reaches the right destination.

So, 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 read it has to read. So, 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. So, in the previous case memory data register in was a 1 that means what basically what happens again as I was telling you that the first microinstruction, the second microinstruction more or less looks similar in case of a read write mode.

This chunk reiterates the change from reading to writing, emphasizing that the data from R1 will be directed to the MDR before it is sent to memory. The system prepares for this by ensuring that the accuracy of the data transfer is maintained - where previously the MDR was in a read mode, it now switches to an input mode (MDR_in set to 1) to receive the data from R1 for storage in memory.

If we go back to our letter analogy, changing modes is like when you decide to take a letter you’ve received (reading) and write your own letter to send out (writing). You transition from reading what someone else has written to crafting your own message and arranging to send that off to a new destination.

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