MCS-51 single-chip computer instruction system shorthand

1. How to memorize mnemonics

1. Table enumeration method

The 44 instruction mnemonics are divided into five categories according to their functions, and each category is memorized in a list.

2. English Restoration Method

The operation code mnemonics of the microcontroller are the English abbreviations of the instruction functions. Converting the abbreviations into the original English text and comparing them with the Chinese text will help you understand the meaning of the mnemonics and thus strengthen your memory. For example:

INC－Incremect DNC－Decrement

Short jump SJMP - Short jump Long jump LJMP - Long jump

Compare jump not equality　

AJMP－Absolute jump NOP－No operation

Exchange XCH－Exchange Addition ADD－Addition

Multiplication MUL－Multiplication Division DIV－Division

RL－Rotate left RLC－Rotate left carry

RR－Rotate right carry RRC－Rotate right carry

3. Functional module memory method

The 44 instruction mnemonics of the microcontroller can be divided into five categories according to their instruction functions, and each category can be divided into 2 to 3 groups based on the principle of similar functions.　 

1) Data transfer group. 2) Addition and subtraction operation group

　　MOV internal data transfer ADD addition

　　MOVC Program memory transfer ADDC Add with carry

　　MOVX External data transfer SUBB Subtraction with carry

3) Logical operation group. 4) Subroutine call group.

　　ANL logic and LCALL long call

　　ORL logical or ALALL absolute call

　　XRL Logical exclusive OR RET Subroutine return

2. How to memorize instructions

1. Symbols of instruction operands

There are six addressing modes of MCS-51: immediate addressing, direct addressing, register addressing, inter-register addressing, indexed addressing, and relative addressing.

1) Immediate value and direct address. ata indicates an eight-bit immediate value, #data16 indicates a sixteen-bit immediate value, and data or direct indicates a direct address.

2) Rn (n=0-7), A, B, CY, DPTR register addressing variables.

3) @R0, @R1, @DPTR, SP represent register address variables.

4) DPTR+A, PC+A represent variables with displacement addressing.

5) PC + rel (relative quantity) indicates a relative addressing variable.

Remembering the mnemonics of instructions and mastering the representation of instruction operands in different addressing modes lays the foundation for us to memorize assembly instructions. Although there are many MCS-51 instructions, they can be divided into five categories according to their functions, including 28 data transfer instructions, 24 arithmetic operations, 25 logical operations, 17 control transfers, and 17 Boolean bit operations. In each category of instructions, according to its function, grasp the different combinations of its source and destination operands, and then use the following methods to remember them.

It is agreed that possible destination operands are represented in the order (# data/direct/A/Rn/@Ri ).

For MOV instructions, the destination operand is written in the order of A, Rn, direct, @Ri, and you can remember the 15 MOV instructions. For example, with accumulator A as the destination operand, you can write the following 4 instructions.

　　MOV A, #data/direct/A/Rn/@Ri

　　And so on, write other instructions.

　　MOV Rn,#data/direct/A

　　MOV direct, #data/direct/A/Rn/@Ri

　　MOV @Ri,#data/direct/A

2. Instruction graphic memory method

The graphic mnemonic method is a mnemonic method that uses graphics and arrows to represent the relationship between the destination and source operands of instructions with the same or similar operating functions but different operands. For example, the instruction to send an array composed of the mnemonics MOV, MOVX, and MOVC can be memorized using Figures 1 and 2.

The four instructions formed by the mnemonic CJNE can also be represented graphically, as shown in Figure 3.

CJNE A,#data,rel CJNE A,direct,rel

CJNE @Rn, #data, rel CJNE @Ri, #data, rel

In addition, for the 18 logical operation instructions formed by (ANL, ORL, ARL), the four ring shift instructions related to A can also be represented by diagrams. Readers are requested to draw them and memorize them by themselves.

3. Classification of similar functions

In the MCS-51 instructions, we found that some instructions have different opcodes, but similar functions and the same operands. The similar function classification method is to memorize instructions with such characteristics together. As long as you remember one of them, you can remember the rest. For example, there are twelve instructions for addition and subtraction, and eighteen instructions for AND, OR, and NOT, which are listed below.

　　ADD/ADDC/SUBB A, #data/direct/Rn/@Ri

　　ANL/ORL/XRL A, #data/direct/Rn/@Ri

　　ANL/ORL/XRL direct, #data/a

　　Each row of instructions above has similar functions and the same operands. Other instructions such as addition (INC) and subtraction (DEC) can also be handled in the same way.