1. Instruction Groups The 8051 has 255 instructions.
The instructions are grouped into 5 groups:
Arithmetic
Logic
Data Transfer
Boolean
Branching
20-Sep-18
Micro 8051

2. Arithmetic Instructions
ADD
8-bit addition between the accumulator (A) and a second operand.
The result is always in the accumulator.
The CY flag is set/reset appropriately.
ADDC
8-bit addition between the accumulator, a second operand and the previous value of the CY flag.
Useful for 16-bit addition in two steps.
20-Sep-18
Micro 8051

3. Arithmetic InstructionsDA
Decimal adjust the accumulator.
Format the accumulator into a proper 2 digit packed BCD number.
Operates only on the accumulator.
Works only after the ADD instruction.
SUBB
Subtract with Borrow.
Subtract an operand and the previous value of the borrow (carry) flag from the accumulator.
A  A - <operand> - CY.
The result is always saved in the accumulator.
The CY flag is set/reset appropriately.
20-Sep-18
Micro 8051

4. Arithmetic Instructions
INC
Increment the operand by one.
The operand can be a register, a direct address, an indirect address, the data pointer.
DEC
Decrement the operand by one.
The operand can be a register, a direct address, an indirect address.
MUL AB / DIV AB
Multiply A by B and place result in B:A.
Divide A by B and place result in A (Quotient):B(Remainder).
20-Sep-18
Micro 8051

5. Arithmetic Instructions
ADD A,Rn Add register to accumulator
ADD A,direct Add direct byte to accumulator
ADD Add indirect RAM to accumulator
ADD A,#data Add immediate data to accumulator
ADDC A,Rn Add register to accumulator with carry flag 1 1
ADDC A,direct Add direct byte to A with carry flag
ADDC Add indirect RAM to A with carry flag
ADDC A, #data Add immediate data to A with carry flag 2 1
SUBB A,Rn Subtract register from A with borrow
SUBB A,direct Subtract direct byte from A with borrow 2 1
SUBB Subtract indirect RAM from A with borrow 1 1
SUBB A,#data Subtract immediate data from A with borrow 2 1
20-Sep-18
Micro 8051

6. Arithmetic Instructions
INC A Increment accumulator
INC Rn Increment register
INC direct Increment direct byte
Incrément indirect RAM
INC DPTR Increment data pointer
DEC A Decrement accumulator
DEC Rn Decrement register
DEC direct Decrement direct byte
Decrement indirect RAM
MUL AB Multiply A and B
DIV AB Divide A by B
DA A Decimal adjust accumulator
20-Sep-18
Micro 8051