addressing modes define how an instruction refers to the operand (the data it will work on). Here’s the breakdown:

**1. Immediate Addressing Mode**

* Definition: The operand (data) is given directly in the instruction itself.
* Interpretation: “Use this constant value.”
* Example ([8051](https://www.ampheo.com/search/8051)/[8086](https://www.ampheo.com/search/8086) style):

`MOV A, #25h ; load the value 25h directly into register A`

* Pros: Fast, no memory access.
* Cons: Value is fixed at compile time, not flexible.

**2. Direct Addressing Mode**

* Definition: The instruction specifies the memory address where the operand is stored.
* Interpretation: “Go to this memory location and get the value.”
* Example (8051):

`MOV A, 30h ; load A with contents of memory address 30h`

* Pros: Simple, explicit access to known memory locations.
* Cons: Only works within the direct address range (in 8051, the lower 128 bytes of RAM or SFRs).

**3. Indirect Addressing Mode**

* Definition: The instruction specifies a register that contains the address of the operand.
* Interpretation: “Look inside this register to find the memory address, then go there for the value.”
* Example (8051, using R0 as pointer):

`MOV A, @R0 ; load A with contents of the memory location pointed to by R0`

If R0 = 40h, then A ← [40h].
* Pros: Flexible, allows dynamic access to arrays, tables, buffers.
* Cons: One level slower (must first read the register to get the address, then fetch data).

**Quick Comparison Table**

**Summary:**

* Immediate = the data itself is in the instruction.
* Direct = the instruction tells you the exact memory address.
* Indirect = a register holds the memory address where the data lives.