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.