FORMAT OF ASSEMBLY LANGUAGE

FORMAT OF ASSEMBLY LANGUAGE

Execution starts at the first line of the program and continues sequentially except for ‘branch’ instructions, until the ‘end ‘ instruction is encountered. The result of each operation is stored in a special word of memory called the “accumulator” (ACC). Assembly language statements are written one per line. Each line of an assembly language program is split into four fields namely:

a.       The Label

b.      Mnemonics

c.       The Operand

d.      The Comment.

THE LABEL

Label is a name use to identify an instruction. It is a name given to memory location where an instruction is stored. Label is a character string beginning in the first column it is optional, it can be placed at the beginning of a statement and it can be used to refer to a memory location of the value of a piece of data of the address of a program, sub-routines, code-portion etc.

Labels are used extensively in programs to reduce reliance upon programmers remembering where data or code is located. A label when declared is suffixed by a colon and begins with a valid character (A-Z). E.g. FIRST: ADD al, 34Hex. The label is used in the program as a reference.

MNEMONICS

Mnemonics is also referred to as Operation code. It is the portion of an assembly language instruction that specifies the operation to be performed. In assembly language, mnemonic form an Operation Code (opcode) is a command such as MOV or ADD or JMP.

For example: MOV, AX, 34Hex where MOV instruction is the opcode and the other parts are called the operands.

THE OPERAND

An operand is the part of an assembly language instruction which specifies what data is to be manipulated or operated on, while at the same time representing the data itself. Operand are manipulated by the opcode. The operand filed consists of additional information or data that the opcode requires.

THE COMMENT

When writing code, it is very helpful to use some comments explaining what is going on. A comment is a section of regular text that the assembler ignores when turning the assembly code into the machine code. The assembly comments are usually denoted with a semicolon. The comment field is optional and is used by the programmer to explain how the coded program works. It is used to make your programs readable and explain what you are doing in English.