Microprocessors and its appliations

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Descriptive Answers (in detail)

  1. Explain the Evolution of Microprocessors.

Microprocessor :

Microprocessor is a multipurpose, programmable, clock-driven, register based electronic device that reads binary instructions from a storage device called memory, accepts binary data as input and processes data according to those instructions, and provides as output.

A common way of categorizing microprocessors is by the number of bits that their ALU can work time. In other words. a microprocessor with a 4. bit will be referred to as a 4-bit microprocessor, regardless of the number of address lines or the number of data bus lines that it has.

  • Intel 4004 :

The first commercially available microprocessor was the Intel 4004. produced in 1971. It contained 2300 PMOS transistors. The 4004~was a 4 bit device intended to be used with some other devices in making a calculator. Some logic designers, however saw that this device could be used to replace PC boards full of combinational and sequential logic devices. Also the ability to change the function of a system by just changing the programming. rather than redesigning the hardware. is very appealing.

  • Intel 8008 :

In 1972 Intel came out with the 8008. which was capable of working with 8-bit words. The 8008,however required 20 or more additional devices to form a func­tional CPU.

  • Intel 8080 :

In 1974 Intel announced the 8080. which had a much larger instruction set than the 8008 and required only two additional devices to form a functional CPU. Also. the 8080 used NMOS transistors. so it operated much faster than the 8008. The 8080 is referred to as a second-generation microprocessor. It reqires +12 V power supply.

  • Motorola MC6800

Soon after Intel produced the 8080. Motorola came out with the MC6800. another 8-bit general-purpose CPU. The 6800 had the advantage that it required only a +5-V supply rather than the -5-V. +5-V. and + 12­V supplies required by the 8080.
For several years the 8080 and the 6800 were the top-selling 8-bit micropro­cessors. Some of their competitors were the MOS Tech­nology 6502. used as the CPU in the Apple II microcom­puter. and. the Zilog Z80. used as the CPU in the Radio Shack TRS~O microcomputer.
Three major directions of microprocessor Evolutions are

  1. Dedicated or Embedded Controllers

  2. Bit Slice Processors

  3. General purpose CPUs

(i) Dedicated or Embedded Controllers:

One direction has been dedicated or embedded controllers. These devices are used to control "smart" machines. such as microwave ovens. clothes washers. sewing ma­chines. auto ignition systems. and metal lathes.

  • Texas Instruments has produced millions of their TMS-1000 family of 4-bit microprocessors for this type of applica­tion.

  • In 1976 Intel introduced the 8048. which contains an 8-bit CPU. RAM. ROM. and some I/O ports all in one 40-pin package. Other manufacturers have followed with similar products. These devices are often referred to as microcontrollers.

  • Some currently available devices in this category-the Intel 8051 and the Motorola MC6801.

  • A more recently introduced single­ chip microcontroller. the Intel 8096. contains a 16-bit CPU. ROM. RAM. a UART. ports. timers. and a 10-bit analog-to-digital converter.

(ii) Bit Slice processors:

A second direction of microprocessor evolution has been bit-slice processors. For some applications. general­ purpose CPUs such as the 8080 and 6800 are not fast enough or do not have suitable instruction sets. For these applications. several manufacturers produce de­vices which can be used to build a custom CPU.

  • An example is the Advanced Micro Devices 2900 family of devices. This family includes 4-bit ALUs. multiplexers. sequencers. and other parts needed for custom-building a CPU. The term slice comes from the fact that these parts can be connected in parallel to work with 8-bit words, 16-bit words. or 32-bit words. In other words. a designer can add as many slices as needed for a particu­ lar application.

  • The designer not only custom-designs the hardware of the CPU, but also custom-makes the instruction set for it using “microcode”.

(iii) General Purpose CPUs

The third major direction of microprocessor evolution has been toward general-purpose CPUs which give a microcomputer most or all of the computing power of earlier minicomputers.

  • Intel 8085 :

After Motorola came out with the MC6800. Intel produced the 8085. an upgrade of the 8080 that required only a +5-V supply.

  • Mototla MC 6809:

Motorola then produced the MC6809. which has a few 16-bit instructions. but is still basically an 8-bit processor.

  • Intel 8086 :

In 1978 Intel came out with the 8086. which is a full 16­bit processor. Some 16-bit microprocessors. such as the National PACE and the Texas Instruments 9900 family of devices. had been available previously. but the market apparently was not ready.

  • Motorola MC68000

Soon after Intel came out with the 8086. Motorola came out with the 16-bit MC68000.

  • The 8086 and the 68000 work directly with 16-bit words instead of with 8-bit words. they can address a million or more bytes of memory instead of the 64 Kbytes addressable by the 8-bit processors. and they execute instructions much faster than the 8-bit processors. Also. these 16­bit processors have single instructions for functions such as.multiply and divtde. which required a lengthy sequence of instructions on the 8-bit processors.

  • The evolution along this last path has continued on to 32-bit processors that work with gigabytes (109 bytes) or terabytes (1012 bytes) of memory. Examples of these devices are the Intel 80386. the Motorola MC68020, and the National 32032.

  1. Explain 8 bit microprocessor in detail.

Some of the 8 bit Microprocessors are:

  • Intel 8008

  • Intel 8080A

  • Intel 8085

  • Motorola MC 6800

  • Zilog Z80

  • Hitachi HD64180

  • Intel 8008 :

In 1972 Intel came out with the 8008. which was capable of working with 8-bit words. The 8008,however required 20 or more additional devices to form a func­tional CPU. It was the first 8 bit microprocessor.

  • Intel 8080A:

8080A is the predecessor of 8085. 8085 has the instruction set of 8080A plus some additional ones. Programs written for 8080A will be executed by 8085. 8085 and 8080A are not pin compatible.

  • Intel 8085:

    • It is capable addressing 64K of memory.

    • It is an enhanced version of its predecessor 8080A.

    • Its instruction set is upward compatible with that of 8080A.

    • The device has forty pins, requires a +5V single power supply, and can operate with a 3-MHz single phase clock.

    • The 8085A-2 version can operate at the maximum frequency of 5 MHz.

    • It has serial I/O ports viz. SID ( Serial Input port ) ,SOD (serial Output port).

    • 8085 is register oriented

    • It has 16 address lines and eight data lines.

    • Eight of its bus lines are multiplexed.

  • Motorola MC 6800

    • Manufactured by Motorola using N-channel MOS technology

    • 8080A and MC6800 were developed as improvements over 8008

    • It has different architecture than its competitor, 8080A

    • It has 16 address lines and 8 data lines

    • It requires +5V power supply.

    • It has two interrupt lines, one is Regular interrupt, another is Non maskable interrupt.

    • Instruction set includes 72 basic instructions.

    • No direct I/O instructions , it has only memory mapped I/O

    • It has simple timing and control signals; the clock period is the same as machine cycle.

  • Zilog Z80:

    • It is manufactured by Zilog using N-channel MOS technology.

    • It is upward compatible with the 8080A.

    • Instruction set has 158 basic instructions, which include 8080 instrcution set. Zilog and Intel mnemonics are different, but machine codes are identical.

    • It is not pin compatible with 8080A or 8085.

    • It dose not include two serial I/O instructions(RIM and SIM)

    • It requires +5V power supply.

    • Clock frequency ranges from 4 MHz to 20 MHz.

    • It has 16 address lines and 8 data lines

    • Two interrupt Lines : One is compatible with 8080A interrupt line, another is a maskable interrupt (NMI)

    • It uses on-board logic to refresh dynamic memories.

    • Instruction Set is the most powerful set among 8 bit microprocessors.

    • It has an extensive set of I/O instructions that include block I/O instructions and various modes of interrupts.

    • It is supported by peripheral devices such as parallel I/O, DMA (Direct memory Access) and the Serial I/O.

      • Hitachi HD 64180:

        • It is 8 bit high integration CMOS microprocessor in a 64 pin package.

        • Designed for low power consumption

        • It can operate with 6 MHz clock.

        • It has 19 address lines , can address upto 512 KB of memory .

        • It includes a clock generator, interrupt controller, memory management (MMU) as support devices for the microprocessor

        • MMU translates internal 64K logical addressing into appropriate physical addressing.

        • It includes 4 I/O related devices.

DMA controller

Asynchronous Serial Communication Interface

Clocked Serial I/O port

Programmable Reload Timer

        • Instruction set is upward compatible with with Z80 instruction set.

        • It has additional instructions including 8 bit multiply and sleep. The Sleep instruction reduces the power consumption to 19 mW.

        • One of the powerful feature of this device is that the opcode fetch cycle of an instruction consists of three T states versus four T states in the Z80, resulting in faster program execution.

Review of 8 bit Microprocessors

  • Architectures of 8085 and Z80 are register oriented.

  • Z80 has a larger instruction set than 8085 and its software compatible with 8085 ,except for serial I/O instruction.

  • MC 6800 is memory reference oriented .It includes fewer registers in its architecture than the 8085.

  • 8 bit microprocessors are used in variety of applications such as appliances, automobiles ,industrial process and control applications.

  • 8 bit microprocessor is too powerful in terms of its capability.

  1. (i) Explain the general features of microprocessors (Cost, Size etc.. ) ?

ii) Compare the microprocessors in terms of Transistors used, clock speed, Data Width and MIPS.
(i) Features:

Cost :

The cost per function goes on decreasing with the increasing complexity of a chip. Volume of production is high. So, it is responsible for the availability of microprocessor chips at fairley low prices.


It is very small size. Because VLSI electronic circuitry has become so dense that a tiny silicon chip can contain hundreds of thousands of transistors constituting the microprocessors.

Power consumption:

Low power consumption. It is manufactured by metal-oxide semi conductor (MOS) technology.


Versatility of microprocessor results from its ‘stored Program’ mode of operation. A microprocessor based system can be configured for numerous applications by altering the software. It is very flexible.


Reliability is high due to lower chip count in the system as compared to its hardwired counter part.
(ii) Compare the microprocessors in terms of Transistors used, clock speed, Data Width and MIPS.

Chip :

A chip is also called an integrated circuit. Generally it is a small, thin piece of silicon onto which the transistors making up the microprocessor have been etched. A chip might be as large as an inch on a side and can contain tens of millions of transistors. Simpler processors might consist of a few thousand transistors etched onto a chip just a few millimeters square.

Date :

The date is the year that the processor was first introduced. Many processors are re introduced at higher clock speeds for many years after the original release Date.

Transistors :

Transistors is the number of transistors on the chip. We can see that the number of transistors on a single chip has risen steadily over the years.


Microns is the width, in microns, of the smallest wire on the chip. For comparison, a human hair is 100 microns thick. As the feature size on the chip goes down, the number of transistors rises.

Clock Speed :

Clock speed is the maximum rate that the chip can be clocked at.

Data Width :

Data Width is the width of the ALD. An 8-bit ALU can add/subtract/multiply/etc. two 8­bit numbers, while a 32-bit ALU can manipulate 32-bit numbers. An 8-bit ALU would have to execute four instructions to add two 32-bit numbers, while a 32-bit ALU can do it in one instruction. In many cases, the external data bus is the same width as the ALU, but not always. The 8088 had a 16-bit ALU and an 8-bit bus, while the modem Pentiums fetch data 64 bits at a time for their 32-bit ALUs.


MIPS stands for "millions of instructions per second" and is a rough measure of the performance of a CPU. Modem CPUs can do so many different things that MIPS ratings lose a lot of their meaning, but we can get a general sense of the relative power of the CPUs from this column.(from the table)

In general, there is a relationship between clock speed and MIPS. The maximum clock speed is a function of the manufacturing process and delays within the chip. There is also a relationship between the number of transistors and MIPS. For example, the 8088 clocked at 5 MHz but only executed at 0.33 MIPS (about one instruction per 15 clock cycles). Modern processors can often execute at a rate of two instructions per clock cycle. That improvement is directly related to the number of transistors on the chip.





Clock Speed

Data Width







8 bits







16 bits, 8 bit bus







16 bits






16 MHZ

32 bits






25 MHZ

32 bits






60 MHZ

32 bits, 64 bit bus


Pentium II




233 MHZ

32 bits,6 4 bit bus


Penium III




450 MHZ

32 bits , 64 bit bus


Pentium IV




1.5 MHZ

32 bitx, 64 bit bus


  1. With a neat diagram, explain the architecture of 8085 microprocessor. Discuss the functions of various signals in 8085?

The 8085 is an 8-bit general-purpose microprocessor capable of addressing 64K of memory.

The diagram shows the logic pin out of the 8085 microprocessor. All the signals can be classified into six groups: (1) address bus, (2) data bus, (3) control and status signals, (4) power supply and frequency signals, (5) externally initiated signals, and (6) serial I/O ports

Address Bus

The 8085 has eight signal lines, AI5-A8, which are unidirectional and used as the high­-order address bus.

Multiplexed Address/Data bus

The signal lines AD7-ADo are bidirectional: they serve a dual purpose. They are used as the low-order address bus as well as the data bus. In executing an instruction, during the earlier part of the cycle, these lines are used as the low-order address bus. During the later part of the cycle, these lines are used as the data bus. (This is also known as multiplexing the bus.) However, the low-order address bus can be separated from these signals by us­ing a latch.

Control and status signals


ALE-Address Latch Enable: This is a positive going pulse generated every time the 8085 begins an operation (machine cycle); it indicates that the bits on AD7-AD0 are address bits. This signal is used primarily to latch the low-order address from the multiplexed bus and generate a separate set of eight address lines, A7-A0.

RD-Read: This is a Read control signal (active low). This signal indicates that the selected I/O or memory device is to be read and data are available on the data bus.

WR-Write: This is a Write control signal (active low). This signal indicates that the data on the data bus are to be written into a selected memory or I/O location.

IO/M: This is a status signal used to differentiate between I/O and memory operations. When it is high, it indicates an I/O operation. when it is low, it indicates a memory op­eration. This signal is combined with RD (Read) and WR (Write) to generate I/O and memory control signals. ­

S1 and S0: These status signals, similar to IO/M, can identify various operations.

Power supply and Clock Frequency :

V cc: +5 V power supply.

V ss: Ground Reference.

Xl, X2: A crystal (or RC, LC network) is connected at these two pins. The frequency is internally divided by two; therefore, to operate a system at 3 MHz, the crystal should have a frequency of 6 MHz.

CLK (OUT)-Clock Output: This signal can be used as the system clock for other devices.

Externally Initiated Signals including Interrupts :

INTR (input) : Interrupt Request. It is used as a general purpose interrupt.

INTA (Output) : Interrupt Acknowledge It is used to acknowledge the interrupt.

RST 7.5 (Inputs) : Restart Interrupts. These are vectored interrupts that transfer the program control to specific memory locations. They have higher priorities than the INTR interrupt. Among these three, the priority order is 7.5,6.5,5.5.

TRAP (Input) : It is nonmaskable interrupt and has the highest priority.

HOLD(Input) : It indicates that a peripheral such as a DMA (Direct memory Access) controller is requesting the use of the address and data buses.

HLDA (Output) : Hold Acknowledge .It acknowledges the HOLD request.

READY(Input) : It is used to delay the microprocessor Read or write cycles until a slow responding peripheral is ready to send or accept data.

RESET IN : When the signal on this pin goes low, the program counter is set to zero, the buses are tristated, and the MPU is reset.

RESET OUT: It indicates that the MPU is being reset.It can be used to reset other devices.

Serial I/O ports:

8085 has two signals for serial transmission : SID(Serial Input Port), SOD(Serial Output Port)

8085 Architecture

It includes the ALU (arithmetic /Logic Unit), Timing and Control Unit, Instruction Register and Decoder, Register Array, Interrupt Control, and Serial I/O Control.


The arithmetic and logic unit performs the computing functions; it includes the accumulator, the temporary register, the arithmetic and logic circuits, and five flags. The temporary reg­ister is used to hold data during an arithmetic and logic operation. The result is stored in the ac­cumulator, and the flags are set or reset according to the result of the operation.

The flags are affected by the arithmetic and logic operations in the ALU.

The flags are :

D7 D6 D5 D4 D3 D2 D1 D0






S- Sign Flag . If D7 =1 , then sign flag is set, otherwise rest.

Z-Zero flag. If ALU operation results in zero, then this flag is set, Otherwise it is reset.

AC-Auxilliary flag. In an arithmetic operation ,when a carry is generated by digit D3 and passed on to digit D4, the AC flag is set. Otherwise it is reset.

P-Parity Flag. If the result of an arithmetic or logic operation has an even number of 1’s then this flag is set. Otherwise it is reset.

CY-Carry Flag. If an arithmetic operation results in a carry, the carry flag is set. Otherwise it is reset.

Among the five flags, the AC flag is used internally for BCD arithmetic; the in­struction set does not include any conditional jump instructions based on the AC flag. Of the remaining four flags, the Z and CY flags are those most commonly used.

Timing and Control Unit

This unit synchronizes all the microprocessor operations with the clock and generates the control signals necessary for communication between the microprocessor and peripherals.


The RD and WR sig­nals are indicating the availability of data on the data bus.

Instruction Register and Decoder.

The instruction register and the decoder are part of the ALU. When an instruction is fetched from memory, it is loaded in the instruction register. The decoder decodes the in­struction and establishes the sequence of events to follow. The instruction register is not programmable and cannot be accessed through any instruction.

Register Array:

Two additional registers, called temporary registers W and Z, are included in the register array. These registers are used to hold 8-bit data during the execution of some instructions. However, because they are used internally, they are not available to the programmer.

  1. Explain the Applications of microprocessors.

  1. Microcomputers

The simplest and cheapest general purpose microprocessor -based systems are “single board microcomputers” with minimum possible hardware & software configuration.

(a)In universities and educational institutions they are used for imparting training to the students

(b)In industries, they are used for evaluation of the microprocessors or for building systems prototype systems.

  1. Liquid Crystal Display (LCD)

It is commonly used in system where low power consumption is necessary.

Examples: Watches, Calculators, Instrument panels and customer electronic displays.

LCD Display consists of crystal material is arranged in segments or in the form of a dot matrix. The crystal material can pass or block the light that passes through; thus it creates a display.

  1. Matrix Keyboard :

It is a commonly used input device when more than 8 keys are necessary. It reduces the number of interfacing devices are required. It requires 8 lines from the microprocessor to make all the connections instead of 16 lines, if the keys are connected in a linear format.

When a key is pressed, it shorts one row and column. Otherwise, the row and column do not have any connection. The interfacing of a matrix keyboard requires 2 ports. (i) Output port (ii) Input port.

In a matrix keyboard, the major task is to identify a key that is pressed and decode the key in terms of its binary value. This task is accomplished through either software or hardware.

  1. Domestic Appliances:

Microprocessors are also being incorporated with relatively simple domestic devices such as Ovens, Washing machines, Air conditioners, Television sets and Alarms. Microprocessor can be used in Automobiles.

  1. Temperature Indicator and Controller

Microprocessors are used in typical process control applications. Microprocessor monitors a process temperature and display it on a 4 digit, seven segment display. The lower and upper limits of the temperature being monitored.

  1. Weight Cost System:

It is to provide a digital display of the weight and the price for an amount of goods.

A pressure transducer is used to generate a voltage that corresponds to the weight of the goods being measured. This voltage is converted within the microprocessor into an 8421 BCD representation of the weight.

  1. Traffic Light Control:

Traffic Light Colors : Green, Yellow and Red

Microprocessors are used to give signal to traffic in traffic light controller.

  1. Instrumentation:

The processing power of the 8 bit microprocessor is more than adequate to satisfy the requirements of most of the instrumentation applications.

Frequency meters, function generators, frequency synthesizers, spectrum analyzers, and many other instruments are available, where microprocessors are used as controllers.Microprocessors are also used in Medical Instrumentation. E.g. Patient Monitoring in Intensive Care Unit, Pathological Analysis and the measurement of parameters like blood pressure and temperature.

  1. Communication :

In the telephone Industry, microprocessors are used in digital telephone sets, telephone exchanges and modems.

Microprocessor is used in Radio, Television and satellite communication.

Microprocessors are making possible implementation of LAN and WAN for communication of varied information through computer network.

  1. Robots:

It is a Numeric controlled machine. Robots are used in the Motor Car and domestic appliance industries.
Descriptive answers in short

  1. Explain the minimum mode operation of 8086 in detail.

When 8086 is in minimum mode

Pin definitions for the minimum mode

Diagrams used for minimum mode system


Timing diagram

  1. What do you mean by Addressing Mode ? What are the different addressing modes supported by 8086 ? Explain each of them with suitable examples.

    • Definition

    • Data Related Addressing modes with examples

  • Immediate

  • Direct

  • Register

  • Register Indirect

  • Register Relative

  • Based Indexed

  • Relative Based Indexed

    • Branch Related Addressing modes

  • Intra segment Direct

  • Intra segment Indirect

  • Inter segment Direct

  • Inter Segment Indirect

  1. Explain the maximum mode operation of 8086 in detail.

        • When 8086 is in maximum mode

        • Pin definitions for the maximum mode

        • Diagrams used for maximum mode system

        • Explanations

        • Timing diagram

  1. (i) Write about instruction formats in 8086 ?

(ii) Explain the special bit indicators in op-code

(iii)What do you mean by ‘Mod’ value in Addressing mode byte ? Give explanation with examples.

Ans :

      1. Instruction formats

One byte to six byte instructions

(ii) Special bit indicators in op-code :

S-bit, W-bit, D-bit, V-bit, Z-bit

(iii)About mod in addressing mode byte with examples

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