15.4. Instruction Cycle

So, we know that while going to execute an Instruction that Instruction Cycle is having basically 2 phase mainly 2 phase. One is your Fetch, second one is Execute and we have seen in the Fetch Cycle what we are going to do we are going to Fetch the Instruction from the Memory and going to bring it to the processor and once we get the Instruction our job is to execute that particular Instruction. So, we are going to execute that particular Instruction inside the processor.

The instruction cycle, which is essential to computer operation, consists of two main phases: Fetch and Execute. During the Fetch phase, the CPU retrieves an instruction from memory, bringing it into the processor where it can be worked on. Once the instruction is fetched, the Execute phase begins, where the CPU performs the operation defined by the instruction.

Think of the instruction cycle like a chef preparing a meal: first, the chef gathers all the ingredients (Fetch), and then cooks the meal (Execute). Without gathering the ingredients first (the Fetch phase), the chef can't start cooking.

Now, here I am giving an example of a program. If you look into it what you are going to get over here some numbers only and along with that we are talking about Memory and CPU Registers. So, basically this CPU Registers is a part of my processor. Inside the processor, we are having storage elements these are the Registers.

In this phase, the CPU uses its registers - small, fast storage locations - to handle data efficiently. For example, when an instruction is fetched from memory, the Program Counter (PC) holds the address of the next instruction, Memory Address Register (MAR) is used to access the memory location, and the Instruction Register (IR) holds the instruction that has just been fetched. This is crucial for keeping track of the instruction sequence.

You can consider registers in a CPU like a small kitchen counter where only a few vital ingredients are kept for immediate use, while the pantry (main memory) holds more supplies. This way, the chef can work quickly without having to run back to the pantry every time they need something.

Now, in CPU Register we are having 3 Register PC, AC and IR. 𝑃𝐶 is the program counter it keeps the address of the next Instruction. We know 𝐼𝑅 which is your Instruction Register where after fetching the Instruction we are going to put it into the Instruction Register, along with that we are having one more Register here which is your 𝐴𝐶. 𝐴𝐶 stands for Accumulator.

The CPU contains several key registers that facilitate instruction processing. The Program Counter (PC) points to the location of the next instruction to fetch. The Instruction Register (IR) stores the fetched instruction, while the Accumulator (AC) is used for intermediate calculations. Together, these registers help the CPU execute programs efficiently.

Imagine a librarian (the CPU) with a list of books to read (the program). The library keeps track of which book to read next (PC), holds the current book being read (IR), and keeps notes of important sections (AC). This organization allows the librarian to work effectively.

After fetching it, now what will happen? We have to increment the values of the program counter. So, that we will be knowing from which Memory location we are going to fetch the next Instruction.

Once an instruction is fetched, its address stored in the Program Counter (PC) must be incremented to point to the next instruction. This ensures a smooth flow of execution, where the CPU sequentially processes each instruction in the program without missing any steps.

Think of a conveyor belt in a factory. After a worker (the CPU) finishes with one product (instruction), they have to move to the next product on the belt (incrementing the PC). This keeps production moving steadily without delays or repetitions.

What does this Instruction mean 1940? We have to see because just looking into it we cannot understand anything, but if we are going to interpret it properly then we are going to get some meaningful information.

Instructions like '1940' appear cryptic, but they actually represent specific operations that tell the CPU what to do, including operations like loading data from memory or executing calculations. To understand these operations, we need a proper instruction format that differentiates between the operation code (opcode) and the address part.

It's much like trying to comprehend a recipe without knowing the cooking terms. If you don't know what 'sauté' means, you can't follow the instructions. Once you understand the terms, you can efficiently follow the recipe.

What is the size of data bus? The size of the data bus is your 16 bits. So, we are going to work with 16 bits of information. Whatever information we are getting is 16 bit.

The data bus determines how much information the CPU can handle at one time. A 16-bit data bus allows the CPU to read or write 16 bits of data simultaneously. This not only enhances processing speed but also increases the amount of data that can be transmitted at any time.

Think of the data bus like a highway. A 16-lane highway (16 bits) can carry more cars (data) simultaneously compared to a 2-lane road (2 bits). A wider highway allows for quicker travel of goods and less congestion.

Now, currently we have discussed about 3 Instructions load Accumulator, store Accumulator, load Accumulator from Memory, store Accumulator to Memory and add Accumulator or add Memory to the Accumulator.

Instruction formats define how various tasks are represented in machine language. Each instruction (like LOAD, ADD, STORE) corresponds to specific operations. Understanding the opcode (operation code) and address references allows for the effective execution of commands by the CPU.

It's like a postal address. Each part of the address tells the postal service what to do: the street name, the house number, city, etc. Without a complete address, the mail won't reach its destination accurately.

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