1.2. Unit Summary

This unit will be mainly focusing on that there are certain instructions whose executions are not sequential, they actually depend on conditions. So, actually they as you all know there is something called program counter which will help us to know what is the next instruction.

This chunk introduces the concept of conditional instructions in programming. Unlike regular instructions that execute one after another in a linear sequence, conditional instructions rely on specific conditions being met before executing a certain instruction. The program counter is a critical component here; it keeps track of which instruction is next. When a conditional instruction arises, it can alter the program counter, leading to jumps in the instruction sequence.

Think of this as navigating a maze. If you always move straight ahead without any decisions, you might hit a wall. Instead, when you encounter a fork in the road (a condition), you must decide whether to turn left or right (execute a different instruction) based on which path looks more promising. The program counter is like your current position in the maze, telling you where to go next.

So, there are two types of conditional instruction that is conditional branch and unconditional branch. Conditional branching means from statement x you go to statement y or you just execute statement x + 1 next instruction depend on some condition like if x > y, then you execute the next instruction.

In this chunk, we learn about the types of conditional instructions. Conditional branches allow the program to take different paths based on whether a specific condition is true or false. For example, if a condition like 'x > y' is true, the program will execute a certain instruction. If it is false, the program may move to a different instruction without executing the one that depends on the condition.

Imagine you are making a decision based on the weather. If it is sunny (condition true), you might go for a picnic (execute the instruction). If it is rainy (condition false), you might choose to stay inside and read a book (skip the picnic and execute a different instruction). This is similar to how programs determine their flow using conditional branches.

In hardware how actually it is reflected? So, it is reflected in terms of certain flag bits which are some registers called the flag registers and inside the flag register there are certain bits allocated for some important parameters like sign, zero, carry, parity, overflow, equality etcetera.

Flag registers are crucial in determining the outcome of conditional instructions. They hold certain bits that represent the status of the last arithmetic or logical operation, such as whether the result was zero (zero flag), or if there was an overflow. These flags inform the CPU about specific conditions, enabling it to make decisions based on the results of previous calculations.

Consider this like the indicators on a car's dashboard. When you see a warning light (like the fuel level being low - a flag), you know you need to take action. Similarly, the flag registers serve as warning lights for the CPU, indicating the results of its previous operations and helping it decide what to do next.

So, in this unit we are also going to look at certain flag bits. And how they are set and how they are reset depending on the arithmetic operation just before a just after going for this instructions corresponding to addition, subtraction, equality checking etcetera.

This chunk discusses how flag bits are manipulated during arithmetic operations. For instance, if a subtraction operation results in zero, the zero flag gets set to indicate that. Conversely, if it does not result in zero, that flag is reset. These settings are essential, as they directly influence the program’s flow when it encounters conditional instructions.

Think of this as a feedback mechanism in a classroom. If students answer a question correctly (the operation results in zero), the teacher gives a thumbs-up (sets the zero flag). If the answer is incorrect, the thumbs-up is removed (reset). This feedback helps guide the teacher on how to proceed with the lesson based on students' performance.

So, what the PSW has? It has lot of components some of them I have listed error status of code, pointer to the next instruction to be executed like in this case it is 7, where I have left sign bits, zero bits, carry bits, reset bits, overflow bits and so many other things which is listed over here.

The Program Status Word (PSW) is crucial for keeping track of a program's state during execution. It contains key information such as the status of various flag bits, the next instruction to execute, and any error codes. This allows the CPU to know exactly where it is in the program and what to do next, especially during jumps or interruptions.

You can think of the PSW as an employee's task list at work. It includes what tasks have been completed (status bits), what tasks need immediate attention (next instruction), and notes about any issues encountered (error status). Just like an employee refers to their list to know what to tackle next, the CPU uses the PSW to guide its operations.

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