30.2.1. Relative Addressing

So, let us write an instruction LOAD IMMEDIATE 20 that is may be the opcode can be something like LDI. [...] It is says load immediate 20.

Immediate addressing means the actual value we want to use is part of the instruction itself rather than being stored in a memory location. In this example, when we use 'LOAD IMMEDIATE 20', we are telling the system to directly load the value '20' into the accumulator. This type of addressing is very straightforward as it requires no further referencing to memory or registers.

Think of this like sending a letter where the message is written directly on the envelope. You don't need to open up the envelope to see what the message is; it's right there, just like how the value '20' is directly in the instruction.

LOAD DIRECT 3 is a direct addressing mode. [...] 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, we refer directly to a memory address. Here, 'LOAD DIRECT 3' means we want to load data from the memory location '3' directly into the accumulator. If we look at memory location '3', we find that it contains the value '20', so that value gets loaded into the accumulator.

Imagine you have a container with numbered slots, and you know that the slot number 3 contains a specific item, say a ball. When you say 'get me the ball from slot 3', you directly access that slot and retrieve the ball, just like accessing memory directly.

Then LOAD INDIRECT 5. [...] So, what is memory location 1 present; that is 49.

Indirect addressing introduces an additional layer of reference. In this case, 'LOAD INDIRECT 5' means that we first check memory location '5', which stores another value, say '1'. We then use that value to find the actual data we want, which is located in memory location '1'. Hence, we load the value '49' into the accumulator through this two-step process.

This method is like asking someone to fetch a book for you. You tell them to first go to a specific shelf (memory location '5') and find the number of the book (which is at location '1'). They go and get that number and then head to another shelf to find the book corresponding to that number.

Then LOAD REGISTER DIRECT 2. [...] So, as I told you our assumption was register 2 has the value 3.

In register direct addressing, the instruction specifies to load data from a register rather than directly from memory. For example, 'LOAD REGISTER DIRECT 2' tells us to load the content of register '2' (which has the value '3') into the accumulator. This means we are directly using values stored in registers rather than going through memory.

Think of this like having a toolbox where each tool is in a specific spot. If I say 'get me the tool at spot 2', you don’t have to look through a warehouse (the memory), because you already know exactly where it is in your toolbox.

But in case of register indirect we first refer to register 2, [...], the content of 20 will be loaded over here.

In register indirect addressing, the register holds the address of the memory location we want to access. If 'LOAD REGISTER INDIRECT 2' is given, it means we first look at register '2' to find out which memory location to access (which contains '3') and then load from that memory location ('3') into the accumulator. This adds flexibility since the memory location can vary depending on the content of the register.

This is like using a map (the register) that tells you where to find a treasure (the data in memory). Your friend (the accumulator) won't know what treasure to look for unless you first check your map for the right coordinates.

But 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.

Displacement addressing is a mix of both memory and register addresses. It typically uses two components: one is a specific memory address and the other is a value from a register. By adding these two values together, we find the effective memory location where the data is located. This mode is often useful for loops and array accessing, enabling you to easily move through contiguous memory locations.

Think of this like using a GPS app to get to a series of locations (like delivering parcels). The app might tell you to start at your current location (the base register) and then drive a specific distance (the displacement or offset) to reach each destination.

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...

Using displacement addressing allows for great flexibility and efficiency, particularly when working with loops or arrays. For instance, if you're writing a piece of code that needs to process multiple items stored in memory, you can start from one memory location and incrementally access subsequent locations by simply adjusting the value in a register. This makes it far easier to manage data structures like arrays where elements are stored in contiguous locations.

Imagine you are reading a book and you decide to read multiple chapters. Instead of flipping back and forth (like referencing different memory locations), you just note the page number of the last chapter you read, then you only adjust the page number as you continue reading—the adjustment is similar to how we adjust using registers.

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