CSNB374: Microprocessor Systems

Chapter 1: Introduction to Microprocessor

Microprocessor-based Computer System A computer system consists of the

following components: Microprocessor (CPU) Memory system I/O system

These three components are interconnected by busses.

This architecture applies to any computer system, from the earlier mainframe computers to the latest systems.

Microprocessor-based Computer System

The Microprocessor (CPU) The controlling element (the brain) of the

a computer system. Controls memory and I/O by executing

program stored in memory. A program is a series of instruction. Instruction is in machine language – string of

0’s and 1’s. The set of instructions used by a CPU is

called the instruction set – unique for each CPU type.

The Microprocessor (CPU) Two main components of a CPU:

Execution Unit (EU) The purpose is to execute instructions Contains the arithmetic logic unit (ALU) Data for operation by ALU are stored registers

Bus Interface Unit (BIU) The purpose is to facilitate communication

between the EU and the memory or I/O. Responsible for transmitting address, data and

control signals on the busses.

Memory System The location where the information

processed by the memory is stored. Each location in memory contains an 8-

bit data (8 bits = 1 byte). The data stored in a memory byte are called

contents. Each memory byte is accessed using an

address. Specified using a hex number.

Memory System Two bytes of data form a word (16 bits). A pair of successive memory bytes can be

treated as a single unit called a memory word. Accessed using the lower address of the two

memory bytes. Intel processors store the least significant byte

in the lower memory address (little endian). Data size can also be in doubleword (32

bits).

I/O System A computer communicates with the

outside world through I/O devices. I/O devices are connected to the

computer through I/O circuits. I/O circuits contains several registers

called I/O ports. Some ports are used for data while others

are used for control commands. I/O ports are accessed using I/O addresses

(similar to memory addresses).

Busses A common group of wires that interconnect

components in a computer system. Three types of busses: address, data and

control. An operation may require data to be

transmitted on all the three busses. Example: memory read. CPU places address of memory location on

address bus. Control signal tells the memory to perform a

read. Data is received from memory on data bus.

Busses

Busses The size of the address bus determines

the maximum memory size that can be supported. 32-bit systems has 32 pins for the address. Can support a maximum of 4GB of memory.

The size of the data bus determines how much data can be transferred at a time.

Many new microprocessors has 64-bit extensions. They have 64-bit data bus. But the address bus is still less than 64-bit.

Number Systems Use of microprocessor requires the working

knowledge of number systems. Binary, decimal, hexadecimal.

Decimal numbers: Base (radix) 10 Contains 10 different digits: 0 to 9 The one we use in everyday life

Binary numbers: Base (radix) 2 Contains only 2 different digits: 0 and 1 The number representation used in digital circuits

Number Systems

Hexadecimal numbers: Base (radix) 16 Contains 16 different digits: 0 to 9, A to

F Normally written with ‘0x’ in front or

with an ‘H’ at the back. Example: 91B716 = 0x91B7 = 91B7H

Used as a compact way to represent binary numbers

Number System Conversions Binary to decimal (example):

10012 = (1x23) + (0x22) + (0x21) + (1x20)

= 8 + 0 + 0 + 1 = 910

Hexadecimal to decimal (example): 610A16 = (6x163) + (1x162) + (0x161) +

(10x160) = 24576 + 256 + 0 + 10

= 2484210

Number System Conversions Decimal to binary (example):

Convert 4310 to binary.

43 / 2 = 21 remainder 121 / 2 = 10 remainder 1

10 / 2 = 5 remainder 05 / 2 = 2 remainder 12 / 2 = 1 remainder 01 / 2 = 0 remainder 1

Therefore, 4310 = 1010112

Number System Conversions

Decimal to hexadecimal (example):Convert 42510 to hexadecimal.

425 / 16 = 26 remainder 926 / 16 = 1 remainder 10 (A)1 / 16 = 0 remainder 1

Therefore, 42510 = 1A916

Conversion Involving Fractional Numbers Binary to decimal (example):

0.0112 = (0x2-1) + (1x2-2) + (1x2-3)

= 0 + 0.25 + 0.125 = 0.37510

10.112 = (1x21)+(0x20)+(1x2-1)+(1x2-2)

= 2 + 0 + 0.5 + 0.25 = 2.7510

Hexadecimal to decimal (example): 0.A816 = (10x16-1) + (8x16-2)

= 0.625 + 0.03125 = 0.6562510

Conversion Involving Fractional Numbers

Decimal to binary (example):Convert 0.37510 to binary.

0.375 x 2 = 0.75 0

0.75 x 2 = 1.5 10.5 x 2 = 1.0 10 x 2 = 0

Therefore, 0.37510 = 0.0112

Conversion Involving Fractional Numbers

Decimal to hexadecimal (example):Convert 0.120849610 to hexadecimal.

0.1208496 x 16 = 1.9335938 1

0.9335938 x 16 = 14.9375 E0.9375 x 16 = 15.0 F0 x 16 = 0

Therefore, 0.120849610 = 0.1EF16

Binary-coded Hexadecimal

Refers to the use of binary to represent a hexadecimal number.

Example:

Hexadecimal Binary

9A 1001 1010

31 0011 0001

F2 1111 0011

DC 1101 1100

Binary and Hexadecimal Arithmetic In general, addition and subtraction in other

number systems are performed in a similar way to addition and subtraction in decimal.

However, there is a minor difference. Addition:

Digit position can only contain the maximum digit permitted by the number system.

If addition of two digits result in a number higher than the maximum digit, there will be a carry.

Subtraction: When a borrow is performed, the borrowed value will

be the value of the number system’s radix.

Unsigned and Signed Integers Unsigned integers can only represent

positive numbers. If the hardware can store 8-bits, the integer

that can be stored ranges from 0 to 255. Signed integers can represent both

positive and negative numbers. The value of the MSB tells whether the

number is positive or negative. If the hardware can store 8-bits, the integer

that can be stored ranges from -128 to +127.

Unsigned and Signed Integers In theory, there are three ways to

represent negative integers in binary: Using a sign bit 1’s complement 2’s complement

Example: Assuming an 8-bit hardware, represents -10 in binary. Using a sign bit: 10001010 1’s complement: 11110101 2’s complement: 11110101 + 1 =

11110110

Unsigned and Signed Integers In all microprocessor systems, signed

integers are represented using 2’s complement.

Advantage of 2’s complement: Subtraction can be performed using

addition. Simplifies the ALU circuitry.

Example: 2010– 1010 = 2010 + (-1010)

= 000101002 + 111101102

= 000010102

Unsigned and Signed Integers

Floating Point Numbers Representing a number as an integer that has

certain number of bits can seriously limit the values that can be represented.

What if we want to represent a very large number? Or a number with decimal point?

Floating point number refers to a way to represent real numbers which supports a wide range of values.

Format: M x 10E

M – mantissa / significand / fraction E – exponent

Floating Point Numbers Example: Representing a very large

number. 5500000000000000000 = 55 x 1017

Example: Representing a number with decimal point. 2.934 = 2934 x 10-3

Single-precision floating point number has 32 bits.

Double-precision floating point number has 64 bits.

Floating Point Numbers

(a)Single precision floating point number format(b)Double precision floating point number format