COS2014 Basic Concepts Department of Computer Science Faculty
of Science RU.
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Assembly Language for Intel- Based Computers, 5 th Edition Kip
Irvine
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Why study assembly language? Learn about computers Computer
architecture Operating systems Data representation Hardware devices
Learn about assembly languages Learn about compiling Learn how to
write embedded programs Learn the assemble language for Intel
80x86
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Welcome to Assembly Language: Definitions Assembly language:
machine-specific language with a one-to-one correspondence with the
machine language for that computer Machine language: The language a
particular processor understands Assembler: converts programs from
assembly language to machine language
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Welcome to Assembly Language: Example Assembly Language:
High-Level Language: Machine language: x = a + b; MOV AX, a ADD AX,
b MOV x, AX A1 0002 06 0004 A3 0000
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Welcome to Assembly Language: Problems with assembly language
Provides no structure Is not portable Applications can be very long
Hard to read and understand Lots of detail required
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Assembly Language Machine language: Machine instructions:
direct instructions to the processor, e.g. to be encoded to control
the datapath A numeric language understood by the processor
Assembly language: Statements (instructions) in short mnemonics and
symbolic reference, e.g. ADD, MOV, CALL, var1, i, j, that have a
1-to-1 relationship with machine instructions Understood by
human
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When you are writing a C program how does a computer look like
CPU, memory, I/O, Operations on variables,
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8 A Model of Computer for C + if for && CPU Memory i,
j, k; xfloat, yfloat; A[0], A[1], i = i + j; xfloat = 1.0; if
(A[0]==0) Program Counter Typed storage
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This model is quite different from what the hardware in a
computer does when you run your program Why a C program code can
run on your computer? Obviously, someone does some translation for
you
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10 MOV AX, a ADD AX, b MUL c MOV x, AX x = (a+b) * b We have
known C compiler Assembly program C program
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We can see that Assembly Lang. is closer to real computer
hardware! From the angle of Assembly Lang., how does a computer
look like?
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12 A Model of Computer for ASM CPU Memory MOV AX, a ADD AX, b
MOV x, AX 010100110010101 a 110010110001010 b 000000000010010 x AX
BX JX... + - PC
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Assembly program/machine code still have some distance to the
real computer hardware. e.g. Multi-core CPU hyperthreading We need
one more level of translation
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Computer Model of a Lower Layer (from Computer Architecture
textbook)
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15 A Layered View of Computer + if for && CPU Memory i,
j, k; xfloat, yfloat; A[0], A[1], i = i + j; if (A[0]==0) Program
Counter CPU Memory ADD AX, b MOV x, AX 010100110010101 a
110010110001010 b 000000000010010 x AX BX JX... + - PC i = i + j;
xfloat = 1.0; if (A[0]==0) MOV AX, a ADD AX, b MOV x, AX xxxxxx
xxxxx
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MOV AX, a ADD AX, b MUL c MOV x, AX From Assembly to Binary
00000000101000010000000000011000 00000000100011100001100000100001
10001100011000100000000000000000 10001100111100100000000000000100
10101100111100100000000000000000 10101100011000100000000000000100
00000011111000000000000000001000 Assembler Assembly Machine
code
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High Level Language Program Assembly Language Program Machine
Language Program Control Signal Compiler Assembler Machine
Interpretation temp = v[k]; v[k] = v[k+1]; v[k+1] = temp; MOVAX,a
ADDAX,b MOVx, AX 0000 1001 1100 0110 1010 1111 0101 1000 1010 1111
0101 1000 0000 1001 1100 0110 1100 0110 1010 1111 0101 1000 0000
1001 0101 1000 0000 1001 1100 0110 1010 1111 ALUOP[0:3]
37 Signed Integers The highest bit indicates the sign 1 =
negative, 0 = positive If the highest digit of a hexadecimal
integer is > 7, the value is negative. Examples: 8A, C5, A2,
9D
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38 Forming Two's Complement Negative numbers are stored in
two's complement notation Complement (reverse) each bit Add 1 Note
that 00000001 + 11111111 = 00000000 Why?
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Binary Addition Starting with the LSB, add each pair of digits,
include the carry if present.
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Hexadecimal Integers All values in memory are stored in binary.
Because long binary numbers are hard to read, we use hexadecimal
representation.
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Translating Binary to Hexadecimal Each hexadecimal digit
corresponds to 4 binary bits. Example: Translate the binary integer
000101101010011110010100 to hexadecimal:
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Converting Hexadecimal to Decimal Multiply each digit by its
corresponding power of 16: dec = (D 3 16 3 ) + (D 2 16 2 ) + (D 1
16 1 ) + (D 0 16 0 ) Hex 1234 equals (1 16 3 ) + (2 16 2 ) + (3 16
1 ) + (4 16 0 ), or decimal 4,660. Hex 3BA4 equals (3 16 3 ) + (11
* 16 2 ) + (10 16 1 ) + (4 16 0 ), or decimal 15,268.
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Data representation: Number systems (bases) Number systems used
Binary: The internal representation inside the computer.
Externally, they may be represented in binary, decimal, or
hexadecimal. Decimal: The system people use. ASCII representations
of numbers used for I/O: ASCII binary ASCII octal ASCII decimal
ASCII hexadecimal
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Data representation: Hex Addition & Multiplication Hex
addition and multiplication tables are large We can still do simple
calculations by hand B852h 23Ah + 5A65h * 100h (Your turn) ABCh
2B3h + E F 0 h * 102h
Data representation: Converting to decimal (Human) conversions
to decimal ABCDh = (((10*16+11)*16+12)*16+13 = 43981 (easier on
calculator)
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Data representation: Your Turn: Conversion problems 111010b =
________ 10 1234 base 5 or (1234) 5 = _________ 10
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Data representation: Conversion from decimal (Human)
conversions from decimal 2748 10 = ??? In hex 2748 = 171 * 16 + 12
171 = 10 * 16 + 11 10 = 0 * 16 + 10 so value is ABCh 2748 = 171 *
16 +12 = (10*16 + 11) * 16 + 12 = 10 * 16 2 + 11 * 16 1 + 12 * 16 0
= ABCh How do we know this is the Hex representation?
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Data representation: Your Turn: Conversion problems Write
decimal 58 in binary. Write decimal 194 in base 5
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Learn How To Do the Following: Form the two's complement of a
hexadecimal integer Convert signed binary to decimal Convert signed
decimal to binary Convert signed decimal to hexadecimal Convert
signed hexadecimal to decimal
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Ranges of Signed Integers The highest bit is reserved for the
sign. This limits the range: Practice: What is the largest positive
value that may be stored in 20 bits?
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Character Storage Character sets Standard ASCII(0 127) Extended
ASCII (0 255) ANSI (0 255) Unicode (0 65,535) Null-terminated
String Array of characters followed by a null byte Using the ASCII
table back inside cover of book
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Numeric Data Representation pure binary can be calculated
directly ASCII binary string of digits: "01010101" ASCII decimal
string of digits: "65" ASCII hexadecimal string of digits:
"9C"
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Character Representation ASCII (Table of ASCII Codes)Table
American Standard Code for Information Interchange Standard
encoding scheme used to represent characters in binary format on
computers 7-bit encoding, so 128 characters can be represented 0 to
31 & 127 are "control characters" (cannot print) Ctrl-A or ^A
is 1, ^B is 2, etc. Used for screen formatting & data
communication 32 to 126 are printable (see the last page in
textbook)
Binary Data Decimal, hex & character representations are
easier for humans to understand; however All the data in the
computer is binary An int is typically 32 binary digits int y = 5;
(y = 0x00000005;) In computer y = 00000000 00000000 00000000
00000101 int z = -5; (y = 0xFFFFFFFB;) In computer, z = 11111111
11111111 11111111 11111011
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Binary Data A char is typically 8 binary digits char x = '5';
(or char x = 53, or char x = 0x35) In computer, x = 00110101 char x
= 5; (or char x = 0x05;) In computer, x = 00000101 Note that the
ASCII character 5 has a different binary value than the numeral 5
Also note that 1 ASCII character = 2 hex numbers
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Storage Size Terminology Byte 8 bits (basic storage size for
all data) Word 16 bits (2 bytes) Doubleword 32 bits (4 bytes)
Quadword 64 bits (8 bytes)
