26.1. Introduction to Micro Instructions

So, basically what we can do is that, we can actually write a 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.

Micro instructions are small instruction sequences that control the operations of the Arithmetic Logic Unit (ALU) within a computer. The text explains how micro routines, which are a set of micro instructions, can be shared and reused for similar operations. For example, the micro routines for 'add' and 'subtract' operations are almost identical except for one control signal that indicates whether to add or subtract. By writing a single micro program that encompasses these common operations, we can optimize the instruction execution process.

Imagine a kitchen where a chef prepares several similar dishes; instead of creating individual recipes for each dish, the chef prepares a base recipe and adjusts just a few ingredients for each dish (like adding sugar to make a cake vs. salt for a soup). This approach saves time and simplifies the cooking process.

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.

The instructor emphasizes two crucial points about the connection between macro instructions and micro instructions. First, this section will explore how to execute complete macro instructions through their underlying micro instructions, providing deeper insights into the execution process compared to the earlier focus on fetching instructions. The student will learn how these lower-level micro instructions work together to fulfill the higher-level commands represented by macro instructions.

Consider a school project where each student (the macro instruction) has specific tasks (micro instructions) that contribute to the overall project completion. Just like every student’s effort from planning to execution matters, each micro instruction plays an important role in executing the macro instruction.

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.

Here, the focus shifts to the optimization of micro instructions. By grouping similar macro instructions, we create a more efficient set of micro instructions, which can be executed interchangeably with minimal adjustments. For instance, the instruction sequences for 'jump on zero' and 'jump on carry' can be similar and allow shared micro programming, thus reducing the need for separate routines and improving execution efficiency.

Think of a factory assembling products. Different models might share many components. By designing a single assembly line that can adapt for different models instead of constructing separate lines for each model, the factory can operate more efficiently and adapt to consumer demand quickly.

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 programs. So, this is not a requirement of the macro program. So, for example, if I have add R1 and R2. So, if this instruction is there you do not require to explicitly write jump instructions in the micro routine because this is not a jump instruction.

In this chunk, the discussion is about two types of jumps: implicit and explicit. Implicit jumps happen automatically within optimized micro routines that handle multiple macro instructions without needing additional commands. For example, an addition operation does not require specific jump commands, as it runs through a common routine. Explicit jumps, however, are necessary when programming directives require a clear, defined movement within the program.

Imagine a GPS navigating through a city. If you enter a single destination, it simply guides you (implicit), but if you enter multiple stops explicitly, it will guide you from one to another. Both processes get you where you are going, but one is direct and straightforward, while the other needs specific instructions.

So, these are the control signals to be generated, this is the branch field address; that means, if you have to jump to some location that value will be given over here that will be loaded to the micro program control unit if and only if the load value is 1.

This section explains the control signals generated during the execution of micro instructions. Control signals direct the micro program control unit on whether to execute certain operations, such as jumping to a different memory location or continuing the current sequence. A branch field address specifies the memory location to jump to, but it only loads if a condition (load value being 1) is satisfied. This control mechanism ensures that the micro instructions operate precisely as intended.

Think of a traffic control system where signals direct the flow of vehicles. A green light (load value = 1) allows cars to proceed (jump to the next instruction), while a red light (load value = 0) forces them to stop (stay at the current instruction). Control signals manage the flow of information, just as traffic signals manage vehicle movement.

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