10.4. Microinstructions

As I told you for example, if I am using this mouse then when I am making a mouse click then your control signal will be read from the control bus by the CPU, it will find out that the mouse click is there then we will it will give command for display. So, whenever the I/O device is involved, memory device is involved, which is out of the CPU then the control bus comes into picture which is taking signals in and out from the control unit.

When a user interacts with an input device like a mouse, the action (like a click) sends a signal to the control unit through a pathway called the control bus. The CPU receives this signal and processes it, determining that an action has occurred, such as needing to update the display. The control bus is crucial because it manages data communication between external peripherals (like input/output devices) and the CPU, ensuring that commands are communicated correctly.

Think of the control bus as a postal service for a city. If you send a letter (the signal) to your friend (the CPU) about a party (a mouse click), the postal service (the control bus) makes sure the information gets delivered correctly. If there are many letters (signals) being sent around, the postal service has to handle them efficiently, just like the control bus manages multiple signals between devices and the CPU.

So, for example, for the time being let us just look at the details of the internal bus. ... these part is your memory, these part is your I/O devices, this part is your memory devices and in fact this is a control bus to for the synchronization.

The internal bus architecture is the structure within the CPU that connects various components such as registers, memory, and I/O devices. This bus facilitates the movement of data within the CPU. It consists of multiple lines for data, along with control lines that synchronize the operations of different components. When one component needs to send or receive data, such as a register needing to load a value from memory, the internal bus handles these transactions efficiently.

Imagine the internal bus as a network of roads in a city. Just like how roads connect houses, schools, and offices (the components), the internal bus connects registers, memory, and I/O devices. Vehicles (data) travel along these roads to deliver messages (instructions) where they need to go, ensuring that everything within the city works together smoothly.

So, if you want to take from any input from the register from the internal bus, then what actually you have to do you have to make R enable that is R = 1. If R is = 1, whatever data is available in the internal processor bus will be fed to R1.

Registers are storage locations within the CPU that hold data temporarily. For any register to receive data from the internal bus, a specific enabling signal (designated as R) must be activated, which is indicated by setting R to 1. This means that if you want to load data into a register (like R1), you must ensure that its enabling signal is set to 1, allowing the data from the bus to flow into that register.

Think of a register as a parking space for cars (data). To allow a new car to park in that space, you need a signal (the enable signal) that says the spot is free. When the signal is on (set to 1), cars can enter (data can be loaded), and when the signal is off (set to 0), that parking space is closed off, preventing new cars from entering.

But we have to be very, very careful that R cannot be more than one for any block which is giving output with register. ... only one register or one ALU or one memory buffer register etcetera is loading into the internal bus.

In the CPU's operation, it's critical that only one component (such as a register) is active in outputting data to the internal bus at any given time. If more than one component tries to send data simultaneously, it can lead to conflicts or 'contention', causing incorrect operations. Therefore, the control unit ensures that only one register or device outputs data to the bus at a time, managing this careful orchestration.

Consider a single microphone being passed around in a classroom discussion. Only one person can speak into the microphone at a time; if two people try to speak simultaneously, their voices will overlap, and no one will understand what either of them is saying. Similarly, in a CPU, only one register should output data at a time to avoid confusion on the internal bus.

Now, who takes care the control unit, because the control unit will generate the signals ... will all depend on the control signals R and R which will be generated by the control unit.

The control unit is the decision-maker in the CPU, responsible for generating the necessary control signals (such as enabling signals for registers). These signals dictate which registers can output data and when, ensuring smooth operation without conflicts. It acts as a conductor in an orchestra, coordinating all components of the CPU to work harmoniously.

Think of the control unit as a traffic light at an intersection. The traffic light controls the flow of cars (data) coming from different directions (registers), ensuring that only one set of cars moves at a time to avoid accidents (conflicts). When the light turns green for a specific direction, only those cars can move, just like the control unit enables specific registers to output data.

Now again if I zoom this next part of it. So, you can see that is basically second part is an ALU. ... where you can get the data values.

The Arithmetic Logic Unit (ALU) is a crucial component of the CPU that performs mathematical and logical operations. It requires two inputs, which usually come from the internal bus and registers. The ALU processes these inputs according to specified operations (like addition or subtraction) and outputs the result back to the internal bus for further use. This process involves careful coordination between the ALU and the control unit, ensuring that the correct data is processed.

You can liken the ALU to a calculator that takes numbers from different sources (like your phone or a notepad) to perform calculations. Just like how you would input two numbers into the calculator to add them together, the CPU sends two data inputs to the ALU. After processing, the result is then displayed, similar to how a calculator shows the final number.

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