28.5.2. Freezing the Memory Buffer Register

So, the threes codes for LDA store and load add and store are this one. That is the opcode is 000 means that it is a load instruction add means 1000 and 0001 for store. And then this is where you have to load the value is FF0. So, this one is going to be the binary. So, if somebody erases this and say this is your first line of code, 000 very difficult to read and understand therefore, we always keep the memories. So, in this case the instruction size is 4 instruction size is 4 + 12 that is 4 × 4 16 bits. So, it is a 16 bit instruction size that you can also think that a memory in this case is a 16 word bit is the word size. So, in all the instructions mainly in this case whatever is discussing for this example are loaded in a single word. So, it is easy to fetch decode and execute next it add FF1.

In computer programming, each instruction that a CPU executes corresponds to a binary code, known as an opcode. Different opcodes represent different operations, like loading data or storing it. For example, the opcode '000' signifies a load instruction, '1000' corresponds to addition, and '0001' indicates a store operation. The standard instruction 'LDA FF0' essentially means 'Load the content located at memory address FF0 into the accumulator'. The instruction size and word size play vital roles in how effectively data can be processed, leading to considerations of efficiency in instruction retrieval from memory. Here, a total of 16 bits are used for the instruction, making it straightforward for the system to fetch, decode, and execute.

Think of an instruction set like a menu at a restaurant. Each item on the menu (opcode) tells the kitchen what to prepare (action). Just as a kitchen can only prepare one item at a time based on the order (instruction size), a CPU processes one instruction at a time. If a dish is complicated and requires multiple ingredients to prepare (like a multi-word instruction), it would take longer and be more complex, just as it becomes easier and faster to order a simple dish.

Now, we see step wise basically what happens, now we will again deal with we have already discussed a similar example beforehand, but now we will see in more depth of the different instructions, even registers and the formats. So, as I told you. So, this is the first instruction to be executed. So, the PC is going to have the value of this one value of the memory location of the first instruction. Then what happen is that. So, in this case. So, this instruction no as I told you we are assuming that this is a 16 bit size.

When a program is executed, the first step is instruction fetching. The Program Counter (PC) plays a vital role here, as it holds the memory location of the current instruction. When we assume the instruction is 16 bits, this means each instruction holds much information about the operation to perform and any involved data. The CPU will reference the memory address held in the PC, fetch the instruction, and then decode it to know what operation it should execute next. This step is crucial for CPU operation, ensuring that instructions are correctly identified and processed in sequence.

Imagine the PC as the person holding a recipe book. Each recipe (instruction) is stored with an address. The person looks at the page number (memory address) to find out what to cook (fetch the instruction) and reads the instructions (decode) to start preparing the dish, ensuring they follow the recipe accurately to create the final dish.

So, what happens is that first the PC is pointing to this instruction, this instruction is going to the memory buffer register and as we know that because of this addressing format each memory location has a single instruction. So, need not worry directly take the value of memory buffer register to instruction register, it will decode it and it will find out that it is asking to load the value of FF0 to accumulator.

During instruction execution, the instructions first pass through the Memory Buffer Register (MBR). Since each instruction corresponds to a specific memory location, there is no confusion in determining what should happen next—the values can directly transfer into the Instruction Register (IR) from the MBR. The IR then decodes the instruction, allowing the CPU to execute it effectively. For example, if the instruction is ‘load from FF0’, the CPU now knows it needs to fetch the content from memory address FF0 into its accumulator for further operations.

Think of the Memory Buffer Register like a delivery truck that brings food from a warehouse (memory). When the truck arrives with the order (instruction), it directly unloads (transfers) the food items into the kitchen (Instruction Register) where the chefs (CPU) can see what they need to do next without confusion. For instance, if there’s a box marked 'FF0', the chef knows to use the contents of that box for cooking.

So, once that is done in step 4 you have to freeze it. So, what happened step 1: I give the address, step 2: I see read then I have to wait for synchronization that the memory function is complete, after it’s complete you read the memory buffer register.

Once the data transfer is complete and safely stored in the Memory Buffer Register, the CPU will execute a 'freeze' operation. This ensures that the data in the MBR remains unchanged as it prepares to be read by the designated register. Essentially, freezing is a precautionary measure to prevent any accidental overwrites or changes while data is being processed. The process involves issuing a series of commands, starting from inputting an address to reading and finally integrating the fetched data without any interruptions.

Consider the freezing operation akin to a chef confirming that a dish is complete and placing it under a heat lamp to keep it warm while plating. The dish is safe and unchanged from this point until it’s ready to serve, just like the data in the Memory Buffer Register remains stable until it's retrieved.

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