Introduction to Microprocessor
The Microprocessor is an electronic logic device having computational and data manipulation capabilities. Due to great invention in semiconductor fabrication technique, it became possible to fabricate the whole central processing unit of computer on a single small integrated chip called as microprocessor. The computer having microprocessor as central processing unit are called as microcomputers. A desktop computer and portable( or mobile ) computers like laptop, notebook, palmtop etc, contains microprocessor as a CPU and hence they come under the category of microcomputer. A microprocessor ( or computer ) understands information's composed of only 0s and 1s. It uses binary numbers for it operations. A binary digit is know as a bit. A group of 8 – bit is called a byte.
Word length of microprocessor or computer
A) The word length of a microprocessor ( or computer )is given as n- bit, where n may be 8, 16, 32 , or 64. B) An 8 – bit microprocessor ( or computer ) can process 8 – bit data at a time, its ALU is designed to process 8 – bit data's . Its general purpose registers which hold data for processing are 8 – bit registers. C) Similarly an 16 – bit and 64 – bit microprocessor can process 632 and 64 – bit of data at a time respectively . D) A processor of longer word length is more powerful and can process data at faster speed as compared to a processor of shorter word length. E) The number of bits that microprocessor ( or computer ) can process at a time is called its word length. It is measure of computing power of a computer.
Features of 8085
Intel 8085 is an 8 – bit, NMOS microprocessor It is a 40 pin IC package fabricated on a single LSI chip. The Intel 8085 uses single of + 5V dc supply for its operation. Its clock speed is about 3MHz. It has 80 basic instructions and 246 0pcodes.
It consists of three main sections. An arithmetic and logic unit (ALU ). Timing and control unit. Set of registers. AN ARITHIMETIC AND LOGIC UNIT. ( ALU ) ALU performs the following arithmetic and logical operations. 1) Addition. 2 ). Subtraction. 3 ). Logical AND. 4 ) Logical OR. 5 ). Logical exclusive.6 ). Complement. 7 ). Increment. 8 ) Decrement. 9 ).Left Shift, Rotate left, Rotate right. Clear, etc.
ARITHICTURE FEATURES of 8085 :1:
TIMING AND CONTROL UNIT : The timing and control unit is a section of the CPU. Its generates timing and control signals which are necessary for the execution of instructions. It controls data flow between CPU and peripherals. It controls the entire operations of the microprocessor and peripherals connected to it. Thus it is seen that timing and control unit of the CPU acts as the brain of the computer system. REGISTERS : Registers are used by the microprocessor for temporary storage and manipulation of data and instructions. Data remains in the registers till they are sent to the memory or I/O devices. Intel 8085 microprocessor has the following registers, 1) One 8 – bit accumulator ( ACC ) ie. Register A. 2) Six 8 – bit general purpose registers. B,C,D,E, H,& L. 3) One 16 – bit stack pointer, ie. SP. 4) One 16 – bit program Counter, ie, PC. 5) Instruction register. 8 6) Status register.
8085 Pin Description
Pin Diagram of 8085 :1:
From this logic pin out of the 8085 microprocessor. All the signals can be classified into six groups. 1). High order address bus. 2). Multiplexed Address/data bus. 3). Power supply & frequency signals. 4). Externally initiated signals. 5). Serial I/O ports. HIGH ORDER ADDRESS BUS: The 8085 has sight signal lines, A18------A15 which are unidirectional and used as the high order address bus. MULTIPLEXED ADDRESS / DATA BUS : The signal lines AD7---------AD0 are bidirectional, they serve a dual purpose. They are used as the low order address bus as well as the data bus.
CONTROL AND STATUS SIGNALS :
This group of signals includes two controls signals ( RD & WR ), three status signals ( IO/M, S1 & S0 ) to identify the nature of the operation, and one special signal (ALE) to indicate the beginning of the operation.
POWER SUPPLY AND CLOCK FREQUENCY.
VCC + 5V Power supply , VSS =ground reference, X1,X2 = These are terminals to be connected to an external crystals oscillator which drives an internal circuitry of the microprocessor to produce a suitable clock for the operation of microprocessor. This signal can be used as the system clock for the devices.
SERIAL I/0 PORT :
The 8085 has two signals to implement the serial transmission, SID ( Serial I/P Data ) and SOD ( Serial O/P Data) 12
Intel 8085 Instructions
Intel 8085 Instructions set
An instruction is a command given to the computer to perform a specified operation on given data. 8085 has 80 basic instructions & 246 Opcodes each instruction contain two parts, Operation code and Operand. The first part of an instruction which specifies the task to be performed by the computer is called Opcode. The second part of the instruction is the data to be operated on and it is called Operand. Example : ADD }-– Opcode, B }-– Operand. MVI }-– Opcode B}---Operand.
Programming of Microprocessor.
The simplest symbolic language used for microprocessor is assembly language. The symbols are called as mnemonics. The language written in the form of mnemonics is called as assembly level language. The mnemonics are alphanumeric representation of instructions .ie. It is an combination of letters to indicate the operation of the instructions. The assembly language program for the addition of two numbers placed in two consecutive memory locations, 2501H and 2502H & the sum is stored in the memory location 2503H Mnemonics: Opcode : Operand. LX1 H,2501H. MOV A,M INX H ADD M 15 STA 2501H.
Today microprocessor based systems are used in almost every sphere of life. Their applications are increasing at very fast rate day by day. These are numerous application of microprocessor. They are used in industry ,instrumentation, transportation, military equipment like tanks, radars etc. banks, business organizations, communication, automatic testing of products, lift control, speed control of motors, automatic control of generators voltage, fuel control of furnaces consumers and commercial applications etc.