ASSEMBLY LANGUAGE INSTRUCTIONS

Machine  language  and assembly  language are already been  discussed in chapter 1. In this chapter  we will discuss  various instructions of 8085 microprocessor  in detail.  Microprocessor  is a programmable  digital circuit comprises of registers flip flop  counters etc. An instruction is a binary pattern  which when  applied  to the microprocessor a specific  task is  performed. The  entire group of instructions  of particular microprocessor  is called  its instruction set. Each microprocessor has its own instruction set. The  instruction of 8085 microprocessor will  not  execute on other  microprocessor. In 8085 microprocessor each  instruction  code is  of 8 bit  hence there  may 28. (= 256) different  binary  patterns  therefore  total 256 instructions and 74  different types  of instruction in its instructions set.

Each  instruction has two  part the opcode and the operand. The opcode defines the  operation to be  performed  and operand specifies the data  on which  the operation is to be  performed.  The operand can be 8/ 16 bit data  memory  location  or register. Some  instruction s may have  one operand some have two   operands and some  do not  have any  operand.  Various  types of instruction formats  are discussed later  in this chapter.

According  to the  size  the instructions may  be of one byte  two byte  or three  byte according  they  require one  two or  three  memory  locations. Later in this  chapter we will  see the  size of various  type of  instructions and how  to identify them.