30.1.2. LOAD DIRECT

So, now let us go to some concrete examples that is let us take a very simple memory which has location from 0 to 7 and the content are 2, 49, 5, 20, 12 like this way. And let us assume that you have a register whose content is 3.

This chunk introduces the concept of memory locations and the example scenario. A memory has locations numbered from 0 to 7, with specific values stored in each location. The text suggests a hypothetical situation in which we also have a register with a value of 3. This setup provides the context for further discussions about load instructions and memory addressing.

Imagine your classroom where each student has a desk (memory location) numbered from 0 to 7. Each desk holds a specific book (content). The teacher (register) has a specific book in hand (value 3), ready to replace or compare it with what's on the students' desks.

So, let us write an instruction LOAD IMMEDIATE 20 that is may be the opcode can be something like LDI. Generally here I have discussed in a more linguistic manner, but we always have a mnemonic for that so it may be LDI that is load immediate or you can put some times a person may call it load indirect also. So, this is LOAD IMMEDIATE 20.

The LOAD IMMEDIATE instruction allows a value to be loaded directly into the accumulator without referring to any memory location. Here, the value 20 is embedded in the instruction itself, which is represented with an opcode (like LDI). This means the CPU can access and load this value immediately into the accumulator.

Think of LOAD IMMEDIATE as a teacher directly handing a book (value 20) to a student (the accumulator) without looking at the desks (memory), where the books are usually stored.

LOAD DIRECT 3 is a direct addressing mode. Direct addressing modes means this 3 actually refer to the memory location 3 where the data is present in the memory location 3 so, direct. So, load accumulator 3; that means, to the accumulator you load the data which is present in memory location 3 that is 20.

In direct addressing mode, specifying 'LOAD DIRECT 3' means to retrieve the value stored in memory location 3 and load it into the accumulator. In our example, memory location 3 contains the value 20, which will be transferred to the accumulator.

Imagine the teacher (the CPU) checking desk 3 directly and taking the book (value 20) from there to give it to the student (the accumulator) instead of picking it from a bookshelf (indirectly referencing).

LOAD INDIRECT 5. Now this is interesting load indirect 5 means accumulator will be loaded with something which is present in memory location 5 memory location 5 has value 1 now it’s an indirect. So, 1 is not the data the data is actually present in memory location one. So, what is memory location 1 present; that is 49.

The LOAD INDIRECT instruction means to read from memory indirectly. When we specify 'LOAD INDIRECT 5', we first check the content of memory location 5, which holds the address 1. Then, we go to memory location 1 to find the actual data, which is 49, and load this value into the accumulator.

This is like telling a student (the accumulator) to look for a book not directly on their desk (desk 5), but to first go check another student's desk (memory location 1) where the actual book (value 49) is located. The student retrieves this book and brings it back.

LOAD REGISTER DIRECT 2. In this case it is referring to register it is saying load register direct 2 that is you load to the accumulator what is available in register number 2.

The LOAD REGISTER DIRECT instruction allows the CPU to load the value found in a specific register (in this case, register 2) directly into the accumulator. If register 2 contains the value 3, this means we are transferring the value of the register to the accumulator.

Imagine the teacher getting a book (value in register 2) from another student's desk (register) and directly giving it to the student (accumulator) without looking anywhere else.

But in case of register indirect we first refer to register 2, register 2 has the value 3; 3 is not the data over here we have to look at the memory location 3 is there where the content of 20 is there the 20 will go to the accumulator.

In register indirect addressing mode, we use the value in a register (in this case, register 2 which equals 3) to determine a memory location. Therefore, we check memory location 3 and load its content (which is 20) into the accumulator.

Think of this as asking the teacher for the desk number (register 2 has value 3), and then the teacher goes directly to that desk (memory location 3) to fetch the correct book (value 20) for the student (the accumulator).

Wherever you talk about displacing displacement basically you will find that there are two components of addresses which will be used together to get the effective one. So, what is the displacement mode it says it has 2 address field one contains an explicit address of main memory say that is a it has some explicit value and the other address field refers to a register whose content something say R.

Displacement addressing mode combines two address components: one is a fixed address in memory and the other refers to a register containing an offset. When we add these two together, we get the effective memory address where the desired data is located. This method is versatile and useful in various situations, including loops and accessing arrays.

Imagine you have a map (the memory address) and instructions that tell you to add a few blocks from your current location (the register value). By combining the two, you can find the exact spot you need to reach.

So, there are lot of advantages of this means compared to the other one there are lot of applicability of this one first is if you think of loops then actually it will go say I want to access 10 memory locations one after the another.

Displacement addressing is particularly beneficial in programming loops because it allows for the efficient access of consecutive memory locations. By simply adjusting the value in the register, it can incrementally access multiple addresses without needing specific instructions for each one.

This is akin to a librarian using a catalog to find books – instead of searching for each book individually, they can move down the row of bookshelves (displacement) using the catalog (register) to access each book (memory location) in succession.

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