Class2

INHA UNIVERSITYINCHEON, KOREA

http://eslab.inha.ac.kr/

IBM PC Assembly Language and Programming by Peter Abel

Chapter 1: Basic Feature of PC hardware

Mohammed Nazim uddin( 나짐 )

Email:[email protected] Hi-tech centre.

- 2 -INHA UNIVERSITYINCHEON, KOREA


Hardware Features

Internal Hardware Processor Memory Register

External hardware Keyboard Monitor Disk CD-ROM



Bits and Bytes

Bits The fundamental building block of computer storage is Bit. A bit may be

• Off 0• On 1



Bytes A group of nine related bits

• The eight data bits provide the basis for binary arithmetic and characters

256(28) – (00000000 ~ 11111111)• One Bit parity.

Rules of Parity• Must be odd in each byte

00001010 00001010(1)

Represents a storage Location



Related Bytes Word

• 2-Byte(16-bit) Double Word

• 4-Byte(32-bit) Quadword

• 8-Byte(64-bit) Paragraph

• 16-byte(128) Kilobyte(KB)

Megabyte(MB)



Number system

Binary Base 2 (0,1)

Binary to Decimal 01000001

• Bits are numbered from the right to left. b8b7b6b5b4b3b2b1b0

• Subscripts represent the place value, e.g. b6 has place value 26

• Conversion to decimal is done by evaluating the polynomial b8*28+ b7*27 + b6*26 + b5*25 +b4*24 +b3*23 +b2*22 +b1*21 + b0*20

In this case, 0+64+0+0+0+0+0+1 = 65



Decimal Base 10( 0 to 9)

Decimal to Binary Divided by 2 Stop when 0 Concatenate the Remainder is reverse order

Example 65 1000001

65 / 2 = 32 r 132 / 2 = 16 r 016 / 2 = 8 r 08 / 2 = 4 r 04 / 2 = 2 r 02 / 2 = 1 r 01 / 2 = 0 r 1



HEXADECIMAL Base 16(0 to 9, A..F)

Binary to Hex Group bits by fours (start-

ing with least significant bits)

Add leading zeros as necessary to complete the last group

Convert each group to the equivalent hex digit

0100 1110b = 4Eh

Hex to Binary Expand each hex digit to

the equivalent 4-bit bi-nary form

• You may omit leading zeros of leftmost digit

37h = 0011 0111b (or 110111b)



Character Data

American Standard Code for Information Interchange (ASCII) A 7-bit binary code for a set of 128 characters Usually occupy a byte of storage

• Leading bit may be ignored or used differently by various programs

A sequence of bytes containing ASCII codes is referred to as an ASCII string



Numeric Data

Binary storage two’s complement, one’s complement, sign and magni-

tude, or biased representations

ASCII storage sequence of ASCII bytes representing the digits of the

number expressed in some radix

Binary Coded Decimal sequence of nybbles representing digits 0-9 of the number



Binary Storage

A pre-arranged storage size is used typically byte, word, doubleword, or quadword

Represent a number in base two and en-code the bits 197d is 11000101b

• at least 8 bits will be required to store this number (leading zeros are added if necessary to fill additional bits for larger storage sizes)



Signed vs Unsigned Codes

Unsigned Byte all 8 bits used to repre-

sent the magnitude of the number

Minimum 0 (zero) is coded as 00000000b

Maximum 255 is coded as 11111111b

Signed Byte two’s complement

code is most common only 7 bits are used for

the magnitude Minimum -128 is

coded as 10000000b Maximum +127 is

coded as 01111111b Zero is 00000000b



Storage Sizes and Ranges

Unsigned Integer Byte

0 to 255 Word

0 to 65,535 Doubleword

0 to 4,294,967,295 Quadword

0 to 18,446,744,073,709,551,615

Signed (2’s Complement Code)

Byte -128 to 127

Word -32,768 to 32,767

Doubleword -2,147,483,648 to 2,147,483,647

Quadword -9,223,372,036,854,775,808 to

9,223,372,036,854,775,807



Binary Arithmetic

Addition Numbers can be added

in any number base Use the same algorithm

you practiced in second grade!

Binary Example: c c c c

10101+ 1111100100

0+0 = 00+1 = 11+0 = 11+1 = 10

1+1+1 = 11



Negative Binary Number A negative binary value is expressed in

Two’s complement notation. Two’s complement

• Reverse the bit• Add 1

Example: +65 Reverse bits

Add 1

Number -65

0100000110111110 1

10111111



Subtraction How to Subtract 42 from 65 ?

65 : +(-43) : = 22



PC Components

System Board Processor, main memory, connectors, hard disk, etc…

Bus A bus with wires attached to the system board connects

the components.

Processor 8088,8086,80286….Pentium

Execution and Bus control unit



AH AL

BH BL

CH CL

DH DL

SP

BP

SI

DI

CS

DS

SS

ES

1

2

3

4

ALU------CU------FLAG

n

BUS control unit

Instruction pointer

||||||||||||||||||||

Instruction Queue

EU: Execution Unit

Program con-trol

BIU: Bus interface Unit

.

.

Execution and Bus control Unit



Intel 8086 Organization

Registers - storage locations found inside the processor for temporary storage of data Data Registers (16-bit)

• AX, BX, CX, DX Address Registers (16-bit)

• Segment registers: CS, SS, DS, ES• Pointer registers: SP, BP, IP• Index registers: SI, DI

Status (Flags) register (16-bit)



Data Registers

The data registers may be used for general purposes, however each has special uses AX : Accumulator BX : Base CX : Count DX : Data

Each byte of the 4 data registers can be ac-cessed independently AH, AL, BH, etc. These are referred to as 8-bit registers, but remember they

are part of an existing register



Memory

8086 - 1 megabyte of memory (220 bytes)Each byte is accessed by specifying an

address (00000h through FFFFFh)20-bit addresses must be formed from 16-

bits of information



0000000400

A0000

B0000

C0000

D0000

E0000

F0000

Interrupt VectorsBIOS and DOS Data

DOS

Application Program Area

Video

Reserved

BIOS



Segment Registers

20-bit addresses are obtained by combin-ing two 16-bit registers, segment:offset Address = segment*16(10h)+offset

Example CS: 010C IP: 14D2 Address = 010C*10+14D2 = 010C0+14D2 Address =

02592Each segment is 64K, segments can start

at any paragraph boundary



Program Segments

During program execution, the segment registers are only changed if memory not currently accessible in an active segment must be accessed

Program bytes are arranged into distinct segments for convenience CS -> segment containing machine instructions SS -> segment containing storage for the stack DS -> segment containing data values and storage ES -> segment for additional data or special memory operations

Programmers must be aware of this organization



Instruction and Stack Pointers

IP contains the address of the next instruc-tion to be executed IP specifies an offset into the CS segment IP is not the operand of any instruction

SP points to the top item on the stack SP is an offset into the SS segment SP can be used as an operand in some instructions



BP and Index Registers

BP is a Base Pointer Specifies an offset into any segment, but most commonly

the Stack segmentSI and DI are called Index registers

They normally specify an offset into the Data segment, al-though they can be used as offsets into any segment

Sometimes they hold a number to be added to the address of an array (index)



Flags

Individual bits are used to store the status of the microprocessor Bits are set or cleared as the result of many operations Bits may be affected indirectly (by the execution of an in-

struction) or directly by an instruction designed to access the status word.

Class2

Technology

place value

data bits

related bitsthe

binary arithmetic

storage location

related bytesword2byte16

ibm pc assembly language

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