The 8051 microcontroller has a total of 111 instructions, which are classified into five categories according to their functions:
1. Data transfer instructions (28 instructions)
2. Arithmetic operation instructions (24 instructions)
3. Logical operation and shift instructions (25 instructions)
4. Bit operation instructions (17 instructions)
5. Control transfer instructions (17 instructions)

Data transfer instructions

Data transfer instructions: transfer the source operand to the target address specified by the instruction lock

Arithmetic instructions

There are 24 arithmetic operation instructions, including four basic arithmetic operation instructions: addition, subtraction, multiplication, and division. There are eight mnemonics used in arithmetic instructions: ADD, ADDC, INC, SUBB, DEC, DA, MUL, and DIV.

1. Ordinary addition instruction (ADD)

2. Addition instruction with carry

3. Add 1 instruction

4. Subtraction instruction with borrow

5. Subtract 1 instruction

6. Multiplication Instructions

7. Division Instructions

Logical operation instructions

Logical operation instructions include: logical operation instructions and shift instructions.

1. Accumulator A clear and invert instructions

2. Logic and instructions

3. Logic or instruction

4. Logical XOR instruction

5. Shift instructions

Circular left shift instruction example diagram: RL A A7←A6←A5←A4←A3←A2←A1←A0 ↓ →---------------------------------------------↑

Example of circular right shift instruction with carry: RRC A
CY→A7→A6→A5→A4→A3→A2→A1→A0
↑ --------------------------------------------------←↓

Bit operation instructions

The 89C51 microcontroller has a rich set of bit operation instructions that can complete operations such as transmission, calculation, and control transfer with bit variables as the object.
1. Bit data transmission instructions

Note: There is no direct transfer instruction between two addressable bits. If you want to complete this transfer, you can use CY as a medium for indirect transfer.

Example: To transfer the number at 30H to 20H, execute the following instructions:
MOV C, 30H;
MOV 20H, C;

2. Bit variable modification instructions

**3. Bit variable logic instructions**

Control transfer instructions

The function of control transfer instructions is to transfer the control program from the original sequential execution address to other instruction addresses. This transfer can be completed through program jump, subroutine call, subroutine return, etc.

1. Unconditional transfer instruction
The function of the unconditional transfer instruction is: when the program executes the unconditional transfer instruction, the program will unconditionally transfer to the address provided by the instruction.

2. Conditional transfer instructions

The conditional transfer instruction is an instruction that transfers according to a certain condition.
When the condition is met, it transfers to a new address (label).
If the condition is not met, the next instruction is executed in sequence.

3. Compare transfer instructions

4. Loop transfer instructions

Instruction time calculation

It takes a certain amount of time for the microcontroller to execute each instruction. Assuming that it takes time T to execute an instruction, it takes time N×T to loop the instruction N times. In actual programming, we often use the instruction DJNZ to achieve the effect of software demonstration.

Example: Assuming that a DJNZ instruction takes 2us and a MOV instruction takes 1us, how long does it take in total to execute the following program?

	  MOV R7, #200; Execute once
DL1: MOV R6, #250; Execute 200 times
DL2: DJNZ R6, DL2; Execute 200×250 times
      DJNZ R7, DL1; Execute 200 times 1234

From the above, it can be inferred that the running time of the entire program is
T = 201×1+200×251×2=100601us=100.601s