An instruction set is a group of commands for a CPU in machine language. The term can refer to all possible instructions for a CPU or a subset of instructions to enhance its performance in certain situations.

An Instruction is a command given to the computer to perform a specified operation on given data. The instruction set of a microprocessor is the collection of the instructions that the microprocessor is designed to execute. The instructions described here are of Intel 8085.

These instructions are of Intel Corporation. They cannot be used by other microprocessor manufactures. The programmer can write a program in assembly language using these instructions. These instructions have been classified into the following groups:


A microprocessor system – there memory microprocessor and the input and output devices- can be thought if in terms of the register it contains random access semiconductor memory is a collection of register .A microprocessor itself consist of general purpose and dedicated registers input and output devices contain register that hold their data.

The function of a microprocessor system is implemented by a sequence of data transfer between register in the memory, the Mp and I/O devices and data transformation that accrue primarily in register within the microprocessor. Each register that can be manipulated under program control is addressable in same manner allowing it to be singled out for use in a data transfer or transformation.

The kinds of individual transfer & transformation possible are specified by the microprocessor instruction sets .each instruction in the set causes one or more data transfer and or transformation. A sequence of instruction consists a program. The content section decode, the program instruction in turn, and using timing signal derived from the system code, content what register transfer or transformation table places and when.

Each is designed to execute particular function set .instruction set one fixed by design cannot be changed Intel 8080 .which came in to market in 1973 has 72 bases instruction and 244 variation 8085 which came in to the market in Jan 1977 is a commercial with lintel 8086 has 74 basic instruction and 246 variation it includes all the 72 instruction of 8080.

The two other instructions in 8085 are RIM & SIM.

8085 is faster than 8080 the program written for 8080 can be run without any modification in 8085 but the user has to be careful where the DELAY ROUTINES are involved because of difference in speed of operation.