Will be useful for B.E students

1. ADDRESSING
MODES OF 8051
Prepared By,
Dr. N. AISHWARYA,
R.M.K College of Engineering and Technology

2. Definition:
The ways in which the operands are represented in an instruction is
called addressing modes.
• In 8051, there are 5 addressing modes.

3. CLASSIFICATION OF ADDRESSING MODES
 Immediate Addressing Mode
 Register Addressing Mode
 Direct Addressing Mode
 Register-Indirect Addressing Mode
 Indexed Addressing Mode

4. IMMEDIATE ADDRESSING MODE
• The data will be specified directly in the source operand.
• Since 8051 Microcontroller is a 8 bit microcontroller, only 8 bit data (2 decimal digits) can
be specified.
• The immediate data will be followed by the symbol #
Example:
 MOV A, #04H- The 8 bit data 04H will be moved to accumulator (A) register.
 MOV R3, #0AE H- The 8 bit data AE is moved to R3 register.
Note: In 8051, A, B and R0-R7 registers will be generally used.
Also, whenever the data starts from A to F, the data must be preceded by 0.
Before Execution After Execution
The value of A---->09 The value of A---->04

5. REGISTER ADDRESSING MODE
• In this mode, both source and destination operands are registers.
Example:
 MOV A, R0- The data which resides in R0 register is moved/copied to A register.
 ADD A, R1- The data in R1 register and A register are summed up and the result is stored
in A register.
Note: Both the source and the destination operand cannot be register banks(R0-R7). For eg,
MOV R3,R7 is not possible. The sequence can be,
MOV A, R7
MOV R3, A
Before Execution After Execution
The value of A---->0C
The value of R0--->09
The value of A---->09
The value of R0--->09
Before Execution After Execution
The value of A---->0C
The value of R1--->09
The value of A---->15
The value of R1--->09

6. DIRECT ADDRESSING MODE
• Here the address of the data is specified either in source operand or destination operand.
Example:
 MOV R2, 04 - The data which resides in memory location 04H is moved to R2 register.
Don’t use # symbol, otherwise 04 becomes data rather than address.
Only the internal memory address (00 to 7F) will be used in this mode.
 Assume the data in 04 address----> 0C.
Before Execution After Execution
The value of R2---->09 The value of R2---->0C

7. REGISTER INDIRECT ADDRESSING MODE
• As the name suggests, the address of the memory location which contains the data (will be
enclosed in square brackets) is specified by registers.
• The @ symbol in the instruction specifies this addressing mode.
• Only R0 and R1 registers can be accessed via this mode.
Example:
 MOV A, @R0-Assume the R0 register is pointing to location 80H. Then the value say 0E
in 80H is moved to A register.
MOV @R1, 85-Assume the value in 85H is 02. This data is moved to the memory location
pointed by R1 register.
In other words, this example moves data from one location to another location.
Before Execution After Execution
The value of A--->0C The value of A---->0E

8. INDEXED ADDRESSING MODE
• In this mode, the effective address is formed by summing up the base register and
accumulator register.
• Base registers-PC (Program counter), DPTR (Data pointer register)
• The destination operand will be always A register.
• The source memory can be accessed only by program memory which is represented by
letter C (means code) in the instruction.
Example:
 MOVC A, @A+PC- Assume the A register holds the value 07H and the PC has the value
4100H. Then, the data in memory location 4107H(4100+07) is moved to A register.
MOVC A, @A+DPTR- The same explanation holds good for this instruction also.

9. THANK YOU!!!