Assembly Language Statements

Assembly language programs consist of three types of statements:

• Executable instructions or instructions
• Assembler directives or pseudo-ops
• Macros

The executable instructions or simply instructions tell the processor what to do. Each instruction consists of an operation code (opcode). Each executable instruction generates one machine language instruction.

The assembler directives or pseudo-ops tell the assembler about the various aspects of the assembly process. These are non-executable and do not generate machine language instructions.

Macros are basically a text substitution mechanism.

Syntax of Assembly Language Statements

Assembly language statements are entered one statement per line. Each statement follows the following format:

[label]   mnemonic   [operands]   [;comment]

The fields in the square brackets are optional. A basic instruction has two parts, the first one is the name of the instruction (or the mnemonic) which is to be executed, and the second are the operands or the parameters of the command.

Following are some examples of typical assembly language statements:

INC COUNT        ; Increment the memory variable COUNT

MOV TOTAL, 48    ; Transfer the value 48 in the

                 ; memory variable TOTAL

ADD AH, BH       ; Add the content of the

                 ; BH register into the AH register

AND MASK1, 128   ; Perform AND operation on the

                 ; variable MASK1 and 128

ADD MARKS, 10    ; Add 10 to the variable MARKS

MOV AL, 10       ; Transfer the value 10 to the AL register