16.3. Control Instructions

These are the 3 Instructions we have designed and the code assigned is your 1, 2 and 5. Other codes are now still available to me. So, now we can design some more Instructions.

In this initial part, the speaker introduces three instructions that have already been designed and assigned specific codes (1, 2, and 5). They indicate that there are other code options still available for creating more instructions.

Imagine you're building a set of LEGO structures and you have completed three models (instructions) with specific identification numbers (codes). You realize you still have more LEGO pieces (codes) to create additional models.

Now, we are saying that we are designing one more Instruction called SUB M. So, it means subtraction. This Instruction is basically nothing but Accumulator is equal to Accumulator minus contents of the Memory.

This chunk describes the design of the SUB instruction, which performs a subtraction operation. It specifies that the instruction will take the value in the Accumulator and subtract the contents of a specified memory location. The result is then stored back in the Accumulator.

Think of the Accumulator as a bank account. If you have $100 in your account (Accumulator) and you want to withdraw$30 (subtract the content of memory), the new balance will be $70.

The Instruction format is the same; whatever we are going to design for all Instructions it is going to follow this particular pattern.

Here, it is established that all newly designed instructions will follow a consistent format. This ensures that they can be easily understood and executed by the processor, promoting better organization and clarity.

Consider a recipe book where all recipes follow the same format. This makes it easier to follow any recipe since they are structured similarly, whether it's a cake or a salad.

Along with this 3, I am going to use one more code this is code 4 which is your subtraction code. Like that we can now add more and more Instructions.

In this section, the speaker discusses the introduction of a new code for subtraction (code 4) and alludes to the potential of expanding the instruction set further. Additionally, there is a transition from using memory references to register references, indicating a change in how data operations can be conducted.

Imagine you have three original colors of paint and you've decided to create gradients by mixing them. By adding a fourth color, you broaden your artistic palette, just as adding a new instruction broadens the capabilities of the processor.

We are saying that we are going to say that this is again say load operation this is your 1 is your 0001, what is your 9, 1001; that means, for load I am returning this particular 0001, but with the most significant bit 0 is going to say that it is a Memory reference and 1 will indicate that it is a Register reference.

This section explains how to differentiate between memory and register references through bits in the instruction code. The most significant bit (either 0 or 1) indicates whether the instruction is referencing memory or a register. This binary differentiation is crucial for understanding which data the instruction will operate on.

Think of this as a postal code that indicates where to send a letter. If the code starts with a '1', it might mean 'send it to an office' while a '0' means 'send it to a home'. Understanding this helps ensure that your message reaches the right place.

So, if I am having say only 8 Registers that we are going to use say R0, R1 to R7, say these are the Registers. Then what will happen in that particular case we don’t require the 12 bits.

This segment discusses the limitation of having only 8 registers and why, due to this limitation, not all bits are necessary for addressing them. The speaker explains how unused bits can be set to zero, optimizing the instruction format.

Consider a parking lot that only has 8 spaces available. Instead of labeling them with an elaborate system that allows for 256 spaces, you would simply label them from 0 to 7, effectively using fewer resources.

Now, in that particular case say if I am going to say 6900. In that particular case what will happen 6 is my decrement...

An increment (INR) or decrement (DEC) operation is explained, which can change the value stored in a register or memory location. The specifics of how this works with codes that refer to those operations are highlighted, along with an efficient way to implement them through counters.

Think of a scoreboard where you increase or decrease the score based on a player’s performance. If a player scores three points, you would add on (increment). If a penalty occurred, you'd take a point away (decrement).