19.1. Finite State Machine Implementation for ADD R1,M

So, first let us take an example called ADD R1,M that is you are taking the memory location value R1 dumping it to R1 after adding it to whatever the content in R1.

This section introduces the instruction ADD R1,M. Here, the operation involves loading the value from a memory location (M) and adding it to the current value in register R1. In simpler terms, it's like taking an ingredient from a cupboard and mixing it with something already in a bowl, making a new total in the same bowl.

Imagine you have a bowl with 5 apples (the current value in R1), and you take 3 more apples from a basket (the memory location M) to add to your bowl. Now you have 8 apples in total in the bowl.

If you look forget about last class we have discussed that these are the series of control instructions, what are the signals involved? Program counter in, program counter out, Z, MFC all the signals whichever we are listed here are actually utilized for this micro-instruction.

This part discusses control instructions and the various signals that direct the operations of the finite state machine during instruction execution. The signals like Program Counter (PC), Z, and Memory Function Complete (MFC) play crucial roles in determining what happens next in the computation process.

Think of these signals as traffic lights and signs at an intersection controlling the flow of vehicles (instructions). The lights tell the cars (the operations in the CPU) when to stop, when to go, and which direction to take.

So, now, first we will say if we remember that first was program counter out that is the PC value will be fed to the memory address register and then you will make it select zero, Add, Z.

In this stage, the program counter (PC) is used to fetch the address of the next instruction to execute. The output of the PC goes to the memory address register (MAR) to identify which memory location should be read. Selecting zero and setting up constants are part of preparing the system to perform the add operation.

Imagine you are following a recipe. The PC is your current position in the recipe (let's say step 3), and you write it down on a notepad (the MAR) so you can easily find which step to follow next. Selecting zero can be likened to noting that no additional steps are required before this step.

Now, we have to put it in PC that now PC is updated. Now, we have to it’s important we are waiting for an external signal this is an external signal.

This segment emphasizes that after updating the PC, the system must wait for an external signal to proceed. This signal indicates readiness for the next action, showing the importance of timing and coordination in processes.

Think of this as waiting for a green light at a traffic signal. No matter how ready you are to go (updating the PC), you must wait for the signal (external trigger) before you can move forward.

So, all these like PC, MAR, read, select 0, ADD, Z they are the control signals which you have to generate.

The discussion here is focused on the control signals necessary for carrying out the instruction. Internal signals such as the PC and MAR need to be set correctly to perform the addition operation accurately and ensure data is fetched and processed in the right order.

It's like having a checklist on a project. Each item (control signal) needs to be completed before you can finish the project (execute the instruction). You can't skip steps, and everything must be in the right order to achieve success.

So, let us assume that this ADD R1,M whatever may be the opcode for this corresponds to first instruction.

This part explains that when the opcode (operation code) for ADD R1,M is recognized, the finite state machine (FSM) is triggered to follow a specific sequence of operations until the instruction is completed.

Think of the opcode as a specific recipe guide. When you pick a recipe (opcode), it leads you through a series of steps (states in FSM) to create a dish (execute the instruction). Each step must be followed in order to make the final dish correctly.

So, whenever the memory is ready you can go to the next state.

The transitions between states depend on conditions such as time (clock pulses) and external signals (like the readiness of memory). The FSM waits for these conditions to be fulfilled before proceeding to the next stage in executing the instruction.

It's like a relay race where the runner can only hand off the baton (move to the next state) once the previous runner crosses the checkpoint (memory readiness). You have to wait for the right moment to move ahead.

Here instruction register out will go to the memory address register in, because you have to fetch another operand from the memory.

This explains the role of the instruction register (IR) in delivering the instruction to the memory address register (MAR) for fetching additional data needed for execution, which is critical for operations that require multiple pieces of data.

Imagine you are packing groceries (instruction). You need to first write down what you need (IR) and then go to the pantry (MAR) to find each item. First, you write the list, then you fetch each item, which resembles how instructions and operands interact in this process.

So, if you remember for all other states, similarly I can complete all the sequences of this state machine design like for 6 this is the state 6.

This part summarizes how the FSM processes through its states until it reaches a conclusion (end). Each state corresponds to an operation that is essential to complete the ADD R1,M instruction, which reflects the cyclical and systematic nature of FSMs in processing instructions.

Think of finishing an art project. You go through various stages—sketch (state), outline (state), color (state), and final touches (state). Each step must be completed perfectly before you can present your completed artwork, just as the FSM must navigate through its states.

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