8051 Assembly Programming

• CPU can work only in binary
• It is difficult for humans to deal with 0’s and 1’s in order to program the computer
• A program that consists of 0s and 1s is called machine language
• Assembly languages were developed to provide mnemonics for machine code instructions.
• Comparing to machine language, Programming in assembly language is easier, faster and less prone to error.
• Assembly language is referred to as low-level language because it deals directly with the internal structure of the CPU and its registers.
• Assembly language programs must be translated into machine code by a program called an assembler.
• Assembly language is a series of lines or statements of assembly language instruction or directives (also called pseudo-instructions).
• Instructions tell CPU what to do and directives give directions to the assembler

Structure of 8051 Program:

	ORG
Label :	mnemonic operands	; comment
	END

• ORG – Indicates the start of the program. It tells the assembler to place the opcode at memory location 0
• END – Indicates to the assembler the end of program or source code
• Label – Allows the program to refer a line of code by name. Any label referring to an instruction must be followed by a colon symbol (:). It is an optional field. Each label name must be unique. Label consists of alphabets A to Z or a to z, numbers 0 – 9, special characters question mark (?), period (.), at (@), underline (_) and dollar ($). First character of label must be alphabetic. Mnemonics and reserved words must not be used as label.
• Mnemonic is the command to CPU
• Operand(s) is the data to command. It is an optional field. Few commands do not need data.
• Comment – Comments may be at the end of a line or on a line by themselves. Comment must begin with semicolon (;). It is an optional field.

Sample Program:

	ORG	; start (origin) at location 0
START :	MOV R1, #23H	; load 23H into R1
	MOV R2, #32H	; load 32H in to R2
	MOV A, #0	; load 0 into A
	ADD A, R1	; add contents of R1 to A. A = A+R1. A = 23
	ADD A, R2	; add contents of R2 to A. A = A+R2. A = 55
	ADD A, #10H	; add constant 10 to A. A = A+10. A = 65
	END	; end of asm source file

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Related topics:
8051 Assembling a Program   |   8051 Assembly Template   |   8051 Simulator   |   8051 Data Types and Directives   |   8051 Instruction Set Overview   |   8051 Instruction Set Summary

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List of topics: 8051

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