Processor :The processor is at the heart of any digital system that uses one at all. It accepts analog data in digital format, manipulates the data in some suitable way, and then generates more analog data as output. In addition to this signal-processing function, the processor will handle interaction with the user by the input and display devices, it will store data in memory and then retrieve it again, and it may communicate with other systems as well.

Memory :The memory is used to support the system's functions. It is common for the system to store large amounts of analog data in digital form and manipulate the stored values. The amount of the memory needed is strongly dependent on purpose of the system.

Input transducers :The transducers convert some physical variable into an analog electrical signal. As an example, a strain gauge may generate a voltage proportional to the force applied to the gauge.

Input signal conditioners and lowpass filters :No matter what electrical levels are produced by input transducers, they seldom are appropriate for the digital system, which commonly needs voltages in the 0-5 V range. The signal conditioner is responsible for altering the input analog signal to this range. In addition, high-frequency components of the input signal are usually regarded as noise and are stripped off by a lowpass filter in order to minimize their effects on the system. Furthermore, the digital sampling done subsequently absolutely requires this step in order to avoid aliasing.

ADC(Analog to Digital Convertor) : an ADC is an electronic device that converts an input analog voltage (or current) to a digital number proportional to the magnitude of the voltage or current. However, there are some non-electronic or only partially electronic devices, such as rotary encoders, can also be considered ADCs. The digital output may use different coding schemes, such as binary, Gray code or two's complement binary.

Microprocessor Programs :The program is responsible for analog data stream(the signal processing) and for the operation of the system itself.It is common for there to be two (or even more) microprocessors in a system so that signal processing and signal operating programs are then distinct.

Communications :It is common for a system to have the ability to pass data to another device, often another device. A common interface for systems is the IEEE 488.2/GPIB/HB instrumentation bus, specially designed for instruments.

Display Devices :These can range from a simple light-emitting diode(LED) to cathode ray tubes(CRT).They can indicate the status of the system.

Input Devices :Common input devices are keypads, potentiometers, optical shaft encoders, and switches . More elaborates devices are those familiar to computer users;joysticks and light pens.

DAC(Digital to Analog Convertor) : DAC converts the abstract numbers into a concrete sequence of impulses that are then processed by a reconstruction filter using some form of interpolation to fill in data between the impulses. Other DAC methods (e.g., methods based on Delta-sigma modulation) produce a pulse-density modulated signal that can then be filtered in a similar way to produce a smoothly-varying signal.

A microprocessor incorporates most or all of the functions of a central processing unit (CPU) on a single integrated circuit (IC).The first microprocessors emerged in early 1970s and were used for electronic calculators, using binary-coded decimal (BCD) arithmetic on 4-bit words. Other embedded uses of 4- and 8-bit microprocessors, such as terminals, printers, various kinds of automation etc, followed rather quickly. Affordable 8-bit microprocessors with 16-bit addressing also led to the first general purpose microcomputers in the mid-1970s.

An inexpensive, very simple, flexible microprocessor-based system has been designed for spectrophotometric data acquisition and paper-tape punch unit control. The interface circuit has been implemented with off-the-shelf components and a low cost development system has been used for software and interface development and testing 'in the field'. The system cam be easily adapted to similar instrumentation.

The widespread use of microprocessors in industrial applications such as process control, data logging, monitoring, etc., demand that the design of such systems be automated. Algorithmic methods are inadequate for this task, as knowledge from several sources needs to be combined to produce the resulting designs. In this paper we present a knowledge-based approach to the design of such systems, which includes the design of the hardware configuration as well as the application software. The knowledge requirements and the functional modules of the design task are elicited, and practical designs are demonstrated.


We know that microprocessor is the CPU of a computer. A microprocessor can perform some operation on a data and give the output. But to perform the operation we need an input to enter the data and an output to display the results of the operation. So we are using a keyboard and monitor as Input and output along with the processor. Microprocessors engineering involves a lot of other concepts and we also interface memory elements like ROM, EPROM to access the memory.

The microprocessor (also called CPU for Central Processing Unit) is the principal element of a computer, it execute a list of instructions, without any decision of its share. These instructions lists are commonly called a program. Each model of microprocessor reads specifics instructions to its design in the form of a basic language which one calls assembler. This programming language is complex to use since it is specific "machine" and coded into hexadecimal (as well as the data what still complicates the programming). The software which we use is written in advanced languages (C, Visual BASIC...) which transpose the programs out of comprehensible assembler by the processor. Except some small improvements, all the microprocessors of the computers of the X86 family include/understand the same assembly language (Pentium, Athlon). The processor does not make any decision, only conditional instructions are influenced by external situations: keyboard, request for service of a peripheral.

The interfaced circuit is varied: memory, I/O ports Nevertheless, all the electronic microprocessor assemblies include a starting program in ROM memory (the contents are not deleted without supply voltage of the circuit). This program makes it possible the microprocessor to carry out its initiation with starting (what it must do like detecting the hard disk, to test the memory). A microprocessor-based system thus consists of several interfaced circuits, for example, ROM memory (obligatory), memory RAM (working memory for the results), wearing of entry (keyboard), wearing of exit (bill-poster) put in parallel.


This work develops a new technique for interfacing the data exchange between the microprocessor-based systems and the external devices. This technique exploits the great capacity of interfacing of Extended Physical Addressing and uses the technique of Direct Memory Access (DMA), increases the frequency of the new bus and improves the speed of data exchange. This Fast Physical Addressing, based on the use of software/hardware system in the microprocessor-based system, has two aims. First, the management of a large external memory capacity, with a reduced use of physical addresses of the microprocessor-based system. Second, the increase of the data exchange speed compared to the Extended Physical Addressing. While using this architecture in microprocessor based system or in computer, the input of the hardware part of our system will be connected to the bus system, and the output, which is a new bus, will be connected to an external device. The new bus is composed of a data bus, a control bus and an address bus.

Interfacing Types

There are two types of interfacing in context of the 8085 processor

Memory Interfacing.

I/O Interfacing.

Memory Interfacing:

While executing an instruction, there is a necessity for the microprocessor to access memory frequently for reading various instruction codes and data stored in the memory. The interfacing circuit aids in accessing the memory.

Memory requires some signals to read from and write to registers. Similarly the microprocessor transmits some signals for reading or writing a data.

But what is the purpose of interfacing circuit here?

The interfacing process involves matching the memory requirements with the microprocessor signals. The interfacing circuit therefore should be designed in such a way that it matches the memory signal requirements with the signals of the microprocessor. For example for carrying out a READ process, the microprocessor should initiate a read signal which the memory requires to read a data. In simple words, the primary function of a memory interfacing circuit is to aid the microprocessor in reading and writing a data to the given register of a memory chip.

I/O Interfacing:

We know that keyboard and Displays are used as communication channel with outside world. So it is necessary that we interface keyboard and displays with the microprocessor. This is called I/O interfacing. In this type of interfacing we use latches and buffers for interfacing the keyboards and displays with the microprocessor.

But the main disadvantage with this interfacing is that the microprocessor can perform only one function. It functions as an input device if it is connected to buffer and as an output device if it is connected to latch. Thus the capability is very limited in this type of interfacing.

Programmable Peripheral Devices

Programmable peripheral devices were introduced by Intel to increase the overall performance of the system. These devices along with I/O functions, they perform various other functions such as time delays, counters and interrupt handling. These devices are nothing but a combination of many devices on a single chip. A programmable device can be set up to perform specific function by writing a code in the internal register. As this code controls the function of the device it's called control word and internal register in which it is stored is called Control Register.

INTEL developed some peripheral devices for processors like 8085/8086/8088. The peripheral devices includes

8255 - Parallel Communication Interface (PPI)

8251 - Serial communication Interface (USART- Universal Synchronous/Asynchronous Receiver/Transmitter)

8257 - DMA Controller

8279 - Keyboard/Display Controller

8259 - Programmable Interrupt controller

8254 - Programmable Timer

Types of Communication Interface

There are two ways in which a microprocessor can connect with outside world or other memory systems.

1.Serial Communication Interface

2.Parallel Communication interface

Serial Communication Interface:

In serial communication interface, the interface gets a single byte of data from the microprocessor and sends it bit by bit to other system serially (or) the interface receives data bit by bit serially from the external systems and converts the data into a single byte and transfers it to the microprocessor.

Parallel Communication Interface:

This interface gets a byte of data from microprocessor and sends it bit by bit to the other systems in simultaneous (or) parallel fashion. The interface also receives data bit by bit simultaneously from the external system and converts the data into a single byte and transfers it to microprocessor.

Consider that we have a microprocessor interfaced to both I/O device and also a memory chip. Now how to select between the two devices according to the requirement?

For this purpose an address decoding circuit is used. An address decoding circuit aids in selecting the required I/O device or a memory chip.


1.The 8255 can be either memory mapped or I/O mapped in the system. In the schematic shown in above is I/O mapped in the system.

2.Using a 3-to-8 decoder generates the chip select signals for I/O mapped devices.

3.The address lines A4, A5 and A6 are decoded to generate eight chip select signals (IOCS-0 to IOCS-7) and in this, the chip select IOCS- 1 is used to select 8255.

4.The address line A7 and the control signal IO/M (low) are used as enable for the decoder.

5.The address line A0 of 8085 is connected to A0 of 8255 and A1 of 8085 is connected to A1 of 8255 to provide the internal addresses.

6.The data lines D0-D7 are connected to D0-D7 of the processor to achieve parallel data transfer.


1.The circuit can be used in 8085 microprocessor system and consist of 16 numbers of hexa-keys and 6 numbers of 7-segment LEDs.

2.The 7-segment LEDs can be used to display six digit alphanumeric character.

3.The 8279 can be either memory mapped or I/O mapped in the system. In the circuit shown is the 8279 is I/O mapped.

4.The address line A0 of the system is used as A0 of 8279.

5.The clock signal for 8279 is obtained by dividing the output clock signal of 8085 by a clock divider circuit.

6.The chip select signal is obtained from the I/O address decoder of the 8085 system. The chip select signals for 7.I/O mapped devices are generated by using a 3-to-8 decoder.

8.The address lines A4, A5 and A6 are used as input to decoder.

9.The address line A7 and the control signal IO/M (low) are used as enable for decoder.

10.The chip select signal IOCS-3 is used to select 8279.


1.It requires two internal address and they are A =0 or A = 1.

2.It can be either memory mapped or I/O mapped in the system. The interfacing of 8259 to 8085 is shown in figure is I/O mapped in the system.

3.The low order data bus lines D0-D7 are connected to D0-D7 of 8259.

4.The address line A0 of the 8085 processor is connected to A0 of 8259 to provide the internal address.

5.The 8259 require one chip select signal. Using 3-to-8 decoder generates the chip select signal for 8259.

6.The address lines A4, A5 and A6 are used as input to decoder.

7.The control signal IO/M (low) is used as logic high enables for decoder and the address line A7 is used as logic low enable for decoder.

First the 8259 should be programmed by sending Initialization Command Word (ICW) and Operational Command Word (OCW). These command words will inform 8259 about the following,

Type of interrupt signal (Level triggered / Edge triggered).

Type of processor (8085/8086).

Call address and its interval (4 or 8)

Masking of interrupts.

Priority of interrupts.

Type of end of interrupts.

Once 8259 is programmed it is ready for accepting interrupt signal. When it receives an interrupt through any one of the interrupt lines IR0-IR7 it checks for its priority and also checks whether it is masked or not. If the previous interrupt is completed and if the current request has highest priority and unmasked, then it is serviced.

For servicing this interrupt the 8259 will send INT signal to INTR pin of 8085. In response it expects an acknowledge INTA (low) from the processor. When the processor accepts the interrupt, it sends three INTA (low) one by one. In response to first, second and third INTA (low) signals, the 8259 will supply CALL opcode, low byte of call address and high byte of call address respectively. Once the processor receives the call opcode and its address, it saves the content of program counter (PC) in stack and load the CALL address in PC and start executing the interrupt service routine stored in this call address.


1. It has limitations on the size of data.

2. Most Microprocessor does not support floating-point operations.

3. Over heating physically.

4. Not bit addressable.


I would lke to thank Gursharanjeet Singh Sir for helping me all the way in making of this term paper.He was always present for clearing of doubts which were confronted by me in making of the microprocessor's term paper.Your helping hand is thouroughly appreciated.






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