Microprocessor is• A multi-purpose, programmable, clock-driven, register-based electronic

device

• A semiconductor device manufactured by using LSI technique, including

ALU, register arrays & control circuits on a single chip, also known as

MPU (microprocessor unit)

Microprocessor does• Read binary instructions from memory

• Communicate with all peripherals (memory & I/Os) using system bus

• Control the timing of information flow

• Perform the computing tasks specified in a program

Key Components Microprocessor

Memory

Input

Output

Terminologies

Hardware: physical components of the system

Program: a set of instructions written for the microprocessor to perform a

task

Software: a group of programs

Operating System: A set of programs to interact between the software and

the hardware through the user

Micro-

processor

Memory

Input

Output

Bit

• Abbreviation for the term “binary digit”

• 0: low, 1: high

Word• A group of bits that microprocessor recognizes & processes at a

time

• Microprocessors are classified according to the word length

(Example: 8-bit microprocessors employs a word length of 8

bits)

Nibble• A group of 4 bits

The first microprocessor, Intel 4004, a 4-bit PMOS microprocessor

was introduced in the year 1971 by Intel Corporation, U.S.A..

Then a 4-bit microprocessor Intel 4040, an enhanced version of Intel 4004 was developed.

In 1972, Intel introduced the first 8-bit microprocessor, Intel 8008

using PMOS technology.

In 1973, Intel introduced a more powerful and faster 8-bit NMOS microprocessor Intel 8080.

In 1975, Intel developed an improved 8-bit NMOS microprocessor,

Intel 8085 which uses only one +5V supply. It is an improved version

of Intel 8080.

In 1978 Intel introduced a 16-bit microprocessor, Intel 8086.

In 1985, first 32-bit microprocessor was developed by Intel 80386.

Then came Pentium, 32-bit advanced processor in 1993.

In 1998 Intel developed another 32-bit low cost processor Celeron based on Pentium-Pro architecture.

In 1999, Intel developed Pentium III.

COMPONENTS OF A MICROCOMPUTER:

Arithmetic

Logic Unit

(ALU)

Control Unit

Memory

OutputInput

CPU

(not included in a single chip)

Inside CPU(*)

• Microcontroller– A device that includes microprocessor, memory, and I/O signal lies on a

single chip (fabricated using VLSI technology)

Micro-

processor

as CPU

Memory

OutputInput

Microcomputer Block Diagram

MPU

Memory I/O

Peripheral Devices

A/D Converter

Timer, Serial I/O

Microcontroller Block Diagram

• Microcomputer– A computer with a microprocessor as its CPU

– It includes microprocessor, memory, and I/O (input/output)

– Microcomputer – a computer with a microprocessor

as its CPU. Includes memory, I/O etc.

– Microprocessor – silicon chip which includes ALU,

register circuits & control circuits

– Microcontroller – silicon chip which includes

microprocessor, memory & I/O in a single package.

MACHINE LANGUAGE: Each machine has its own set of instructions based on the design of its CPU or of its microprocessor. To communicate with the computer, one must give instructions in binary language, which is called Machine Language.

ASSEMBLY LANGUAGE: It is difficult for most user to write programs in sets of 0s and 1s. So computer manufacturers have devised English-like words to represent binary instructions of a machine called Assembly

Language, which is machine specific.

LOW LEVEL LANGUAGE: Machine language and Assembly language

are microprocessor specific and are both considered Low Level Language.

HIGH LEVEL LANGUAGE: Programming languages that are intended to be machine-independent are called High-Level Languages. Examples are

FORTRAN, BASIC, PASCAL, C,C++,JAVA etc.

A program called Interpreter or Compiler accept English like statements as their input, called SOURCE CODE. The Compiler or Interpreter

then translates it into OBJECT CODE compatible with the microprocessor being used in the system.

DIFFERENCE BETWEEN COMPILER AND INTEPRETER: The compiler reads the entire program first and translates it into the object code that is executed by the microprocessor. The Interpreter reads one instruction at a time, produces its object code, and executes it before reading the next one.

MACHINE LANGUAGE

• 8085 Machine Language

– 8-bit word length

– Its instruction set (language) is designed by using various combination of

these 8 bits

– 246 different bit patterns, 74 different instructions

– Examples:

0011 1100: increments the number in the accumulator by 1

1000 0000: adds the number in the register called B to the number in the

acc.

keeps the sum in the acc.

• Machine Language is

– A binary language, composed of 0s & 1s

– Specific to each computer

– Tedious & error-prone to recognize & write instructions

– Using Hex keys can be a little bit more effective; still got a problem

Memory Subsystem Organization and Interfacing

• Types of Memory• CACHE MEMORY

• MAIN OR PRIMARY MEMORY

• SECONDARY OR AUXILIARY MEMORY

• ROM

• PROM (Programmable ROM)

• EPROM(Erasable PROM)

• EEPROM(Electrically Erasable PROM)

• Flash EEPROM

RAM

• Static RAM(SRAM)

• Dynamic RAM(DRAM)

Intel 8085 microprocessor family

• Intel 8085 had single 5 Volt power supply.

• It is a 40 pin I.C. package fabricated on a single LSI chip.

• Clock oscillator and system controller were integrated on the

chip.

• Its clock speed is about 3 MHz. The clock is about 320 ns. The

CPU included serial I/O port. • It has 80 basic instructions and 246 op codes.

• It consists of three main sections:

An arithmetic and logic unit.

A timing and control unit.

A set of registers.

• System Bus – wires connecting memory &

I/O to microprocessor– Address Bus

• Unidirectional

• Identifying peripheral or memory location

– Data Bus

• Bidirectional

• Transferring data

– Control Bus

• Synchronization signals

• Timing signals

• Control signal

• Bus

BUS STRUCTURE IN 8085

Address bus signals, Data bus signals

AD0-AD7, A8-A15

16 address lines – 2 sets

Most significant bits (A8-A15) – single directional

Least significant bits (AD0-AD7) – bidirectional

○ Multiplexed with the bits of bi-directional data

bus

○ It is used as both address and data bus

Mp Communication And Bus Timings - 2

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zoom

back

back

•

• A, B, C, D, E, H, and L

• BC, DE, and HL

•

• Program Counter

• Stack Pointer

Status lines:• IO/M Differentiate I/O and memory applications

High – I/O Low – Memory

• S1, S0 – status signals, to indicate the type of machine cycle in progress

Control lines:• RD, WR & INTA RD – data on the data bus to be read into processor WR – data on the data bus to be written to processor INTA – acknowledge an INTR interrupt

__

_

__

• Initiated signals– Reset In – reset CPU

– Hold – suspend CPU operation

– Ready – CPU go into wait state, to sync with slower devices

• Signal acknowledgement– Reset out – high once CPU is rest

– HLDA – acknowledges hold signal

16 – Bit Registers

Program Counter

○ A pointer to the next instruction to be executed

○ Contains the 16-bit memory address of the next instruction

○ Updated after processor has fetched the instruction

Stack Pointer

○ Stack – an area in memory in which temporary info is stored

○ Stack – FILO (First In Last Out) basis

○ Holds the address of the top of the stack

Flag Register› 8 bit register – shows the status of the microprocessor

before/after an operation

› S (sign flag), Z (zero flag), AC (auxillary carry flag), P (parity flag) & CY (carry flag)

› Sign Flag Used for indicating the sign of the data in the accumulator

The sign flag is set if negative (1 – negative)

The sign flag is reset if positive (0 – positive)

D7 D6 D5 D4 D3 D2 D1 D0

S Z X AC X P X CY

Zero Flag

Is set if result obtained after an operation is 0

Is set following an increment or decrement operation of that

register

Carry Flag

Is set if there is a carry or borrow from arithmetic operation

10110011

+ 01001101

---------------

1 00000000

1011 0101

+ 0110 1100

---------------

Carry 1 0010 0001

1011 0101

- 1100 1100

---------------

Borrow 1 1110 1001

Auxiliary Carry Flag

Is set if there is a carry out of bit 3

Parity Flag

Is set if parity is even

Is cleared if parity is odd

1011 0101

+ 0110 1100

---------------

1 0010 0001

• Maskable Interrupts

– Microprocessor can ignore or delay interrupt request

• INTR – General purpose interrupt

• RST 5.5, RST 6.5, RST 7.5 – Restart interrupts, higher priorities

• Nonmaskable Interrupts

– Enabled by default

– Cannot be disabled

– Microprocessor must respond to it immediately

• TRAP – highest priority