26.2. Execution of Macro Instructions

So, basically what we can do is that, we can actually write micro routines which can be shared. For example, as I told you like add and sub. So, most of the case will be similar excepting 1 bit position or the 1 control signal corresponding to add or subtract of the ALU. So, you can try to do basically write a basically a single micro program for similar type of basically macro micro instruction macro instructions, which are common in type.

This segment introduces the concept of writing common micro routines that can be shared among different macro instructions, like addition and subtraction. Both operations share a similar structure but differ in specific bits or control signals. Thus, a single micro program can be developed to handle similar macro instructions efficiently, reducing redundancy.

Imagine a restaurant that serves both pizza and pasta. The base ingredients and cooking methods are mostly the same, but they need a unique topping or sauce to differentiate each dish. By creating a single recipe (micro program) that can handle both pizzas and pastas, the chef can save time and maintain consistency.

Now, let us again now actual I will tell you two things, two things are very important over here. So, as I told you in the last class that in this unit we will also see how a complete macro instruction is executed in terms of micro instructions. Because in the last unit we just saw that how to do a fetch here we will see how a total instruction is executed.

This excerpt emphasizes the importance of understanding how macro instructions are executed using micro instructions. In previous lessons, the focus was on fetching operations. Now, the goal is to delve deeper into the complete execution cycle of a macro instruction, highlighting the series of micro instructions that facilitate this process.

Think of this like teaching a student how to complete a math problem step-by-step. Initially, you might show them just how to write down the problem (fetching). But now, you're guiding them through each mathematical operation and thought process until the problem is completely solved (macro instruction execution).

Secondly, as I told you we also give some idea that how micro instructions can be macro instruct micro instructions corresponding to different type of similar macro instructions can be clubbed. Right for example, we are going to show you how a complete macro instruction is executed in terms of micro instruction, and we were going to take the help of jump on zero 𝑀 (𝐽𝑀𝑃𝑍 𝑀)...

The speaker explains how similar macro instructions allow for the creation of a common micro routine that can execute various similar operations, like 'jump on zero' and 'jump on carry'. This commonality simplifies the instruction set, allowing the micro program to transition between different macro operations depending on specific conditions with minimal changes.

Consider a multi-tool that combines several tools into one device, like a Swiss Army knife. Instead of carrying a separate knife, screwdriver, and scissors, you have everything in one place. This approach saves space and effort while being functional for multiple tasks (macro instructions) with a single solution (micro routine).

So, this type of branching will be actually called the implicit jumps we have to do, because you are writing a common micro program for different macro program... So, this is actually the implicit jump routine, which will be there in the micro program, and then another type of jumps which will be there which are actually explicitly mention in the macro instruction.

This section describes the difference between implicit and explicit jumps in the context of micro programming. Implicit jumps occur when transitioning between different macro instructions within a common micro routine. Explicit jumps are defined by specific instructions like 'jump if zero' and must be incorporated into the micro routine directly, necessitating precise control.

Imagine following a recipe. Sometimes, you seamlessly transition from one step to the next without much thought (implicit jump). However, when the recipe instructs you to go back to a certain step if a condition is met, like checking if the oven is preheated before placing cookies inside, that's similar to an explicit jump.

Let us assume that we have we are going to write a common routine corresponding to jump on 𝑍 to 𝑀 and jump on carry to 𝑀... So, this figure if you look at. So, this is already we have discussing in the last unit just a refresh. So, these are the control signals to be generated, this is the branch field address;

In this segment, the various jump instructions are further illustrated using common routines based on conditions like jumping when the zero flag is set or when a carry occurs. It highlights how control signals are generated to facilitate these actions, detailing the flow of program execution based upon the status of flags and signals.

Picture a traffic light system. Green signals allow traffic to flow smoothly (executing a routine), but if certain conditions are met, such as an emergency vehicle approaching (like a carry or zero flag), the system then directs traffic to a stop or redirect flow (triggering a jump).

If the 0 flag is set, if the 0 flag is set then you are going to execute this one... so, it says that if it is jump on 0, if it is 0 then basically you have to load the value of 𝑃𝐶 = 𝑀 otherwise basically you have to go to number 6 micro instruction...

This part provides a detailed flow of micro instructions based on the state of the zero flag. It describes how, if the zero flag is set, the execution path leads to a change in the program counter to point to a specific memory location, while if it is not set, the process will continue along a different pathway.

Think of a decision-making tree. If you're on a path and you find a checkpoint (zero flag), you have to decide whether to proceed down one route or switch paths entirely. Each decision leads you to a different outcome, just like how different flag states can lead to varying instruction executions.

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