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How to Program and Interface the 8085 Microprocessor: A Practical Approach with Examples and Projects

8085 Microprocessor Programming and Interfacing PDF 13

If you are interested in learning about the basics of microprocessors and how to program and interface them using the 8085 microprocessor, then this article is for you. In this article, you will learn about the following topics:

8085 microprocessor programming and interfacing pdf 13

  • What is a microprocessor and what are its applications?

  • What is the 8085 microprocessor and what are its features?

  • How to understand the architecture of the 8085 microprocessor?

  • How to write assembly language programs using the 8085 instruction set?

  • How to interface the 8085 microprocessor with various input/output devices and memory?

This article is based on the book "The 8085 Microprocessor: Architecture, Programming and Interfacing" by K. Udaya Kumar and B.S. Umashankar, which is a comprehensive textbook for an undergraduate course on the 8085 microprocessor. You can download the PDF version of this book from Google Drive.


What is a microprocessor?

A microprocessor is a small electronic device that can perform arithmetic and logical operations on binary data. It is also known as a central processing unit (CPU) or a processor. A microprocessor consists of three main components:

  • An arithmetic logic unit (ALU) that performs calculations and comparisons.

  • A control unit (CU) that controls the execution of instructions.

  • A set of registers that store data and addresses.

A microprocessor can communicate with other devices such as memory, input/output devices, etc. through a set of wires called a bus. A bus consists of three types of lines:

  • Data lines that carry binary data.

  • Address lines that specify the location of data or instructions.

  • Control lines that indicate the direction and timing of data transfer.

A microprocessor can execute a sequence of instructions stored in memory. Each instruction consists of an operation code (opcode) that specifies what operation to perform, and an operand that specifies where to get or store data. An instruction can be classified into three types:

  • Data transfer instruction that moves data between registers, memory or I/O devices.

  • Arithmetic instruction that performs addition, subtraction, multiplication or division.

  • Logical instruction that performs bitwise operations such as AND, OR, XOR, NOT, etc.

A microprocessor can also perform branching or looping instructions that alter the sequence of execution based on certain conditions. For example, a jump instruction can transfer the control to a different location in memory, and a loop instruction can repeat a block of instructions until a condition is met.

What is the 8085 microprocessor?

The 8085 microprocessor is an 8-bit microprocessor that was developed by Intel in 1976. It is one of the most popular and widely used microprocessors in the history of computing. Some of the features of the 8085 microprocessor are:

  • It has a 40-pin dual in-line package (DIP) that can be easily inserted into a socket.

  • It has an 8-bit data bus and a 16-bit address bus, which means it can access up to 2^8 = 256 bytes of data and 2^16 = 65,536 bytes of memory.

  • It has a clock frequency of 3 MHz, which means it can execute up to 3 million instructions per second.

  • It has a single +5V power supply, which means it consumes less power and generates less heat.

  • It has an internal register set of six general-purpose registers (A, B, C, D, E, H and L), one accumulator (A), one stack pointer (SP), one program counter (PC) and one flag register (F).

  • It has an instruction set of 74 instructions, which include data transfer, arithmetic, logical, branching, looping and stack operations.

  • It has five interrupt signals (INTR, RST 5.5, RST 6.5, RST 7.5 and TRAP) that can be used to request the microprocessor to perform a specific task.

  • It has one serial input/output port (SID and SOD) that can be used to communicate with other devices using serial communication.

Why learn 8085 microprocessor programming and interfacing?

Learning 8085 microprocessor programming and interfacing can have many benefits for students, hobbyists and professionals. Some of the reasons are:

  • It helps you to understand the basic concepts of microprocessors and how they work.

  • It helps you to develop your logical thinking and problem-solving skills.

  • It helps you to write efficient and optimized programs using assembly language.

  • It helps you to interface various devices such as keyboards, displays, sensors, actuators, etc. with the microprocessor.

  • It helps you to design and implement simple projects such as calculators, games, timers, etc. using the microprocessor.

  • It helps you to prepare for advanced courses on microcontrollers, digital signal processors, embedded systems, etc.

Architecture of the 8085 microprocessor

Pin diagram and description

The pin diagram of the 8085 microprocessor is shown in Figure 1. The pins are numbered from 1 to 40 in an anti-clockwise direction. The pins can be classified into six groups:

Group Pins Description --- --- --- Power supply and frequency Vcc (40), Vss (20), X1 (1), X2 (2), CLK OUT (37) Vcc and Vss provide +5V and ground supply respectively. X1 and X2 are connected to a crystal oscillator that generates the clock signal. CLK OUT provides the clock output for synchronizing other devices. Data bus AD0-AD7 (12-19) These are bidirectional lines that carry the lower 8 bits of address or data. They are multiplexed to save pins. Address bus A8-A15 (21-28) These are unidirectional lines that carry the higher 8 bits of address. They are used along with AD0-AD7 to form a 16-bit address. Control and status signals ALE (30), IO/M' (34), RD' (32), WR' (31), S0 (29), S1 (33) ALE is an output signal that indicates when AD0-AD7 carry address or data. IO/M' is an output signal that indicates whether the operation is memory or I/O. RD' and WR' are output signals that indicate whether the operation is read or write. S0 and S1 are status signals that indicate the type of operation being performed. Interrupts INTR (36), INTA' (35), RST 7.5 (39), RST 6.5 (38), RST 5.5 (37), TRAP (40) These are input signals that 71b2f0854b


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