1 Chapter 1: Introduction Appendix A: Binary and Hexadecimal Tutorial Assembly Language for Intel-Based Computers, 3rd edition Kip R. Irvine

Introduction  1.1 Context of assembly language (Important: Read this section!)  1.2 Data representation  A.1 Binary numbers  A.2 Hexadecimal numbers  A.3 Arithmetic  1.3 Introducing assembly language

1.1 Context of assembly language: Why study assembly language (ASM)? n To learn how high-level language (HLL) code gets translated into machine language 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

1.1 Context of assembly language: Example High-Level Language: ; Machine language: B MOV AX, 10 ADD AX, 20 Assembly Language: Immediate operand op code

n To learn the computer (i.e., architecture, hardware, operating system…) u by direct access to memory, video controller, sound card, keyboard… u by communicating with the operating system n To speed up applications u direct access to hardware (ex: writing directly to I/O ports instead of doing a system call) u good ASM code is faster and smaller u Avoid restrictions of high level languages 1.1 Context of assembly language: Why study assembly language (ASM)?

1.1 Context of 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

1.2 Data representation: Binary Numbers  Digital computers store information in binary  Binary allows two states –On yes true 1 –Off no false 0  Each digit in a binary number is called a bit ff on on off bit

1.2 Data representation: Data types  byte: 8 bits:  word: 16 bits or __ bytes:  double word: __ bits or __ bytes :  quad word: __ bits or __ bytes:

1.2 Data representation: Range of a unsigned number  Question: What is the range of numbers that can be represented with ?  2 bits?  4 bits?  1 bit?  n bit?

1.2 Data representation: Range of the data types  byte: 0 to = 255  word: 0 to = 64k - 1 = 65,535  double word: 0 to  quad word: 0 to Unsigned integers:

1.2 Data representation: Numbering Systems  A number system of base n is a system that uses distinct symbols for n digits

 A written number is meaningful only with respect to a base 1.2 Data representation: Numbering Systems  To tell the assembler which base we use: –Hexadecimal 25 is written as 25h –Octal 25 is written as 25o or 25q –Binary 1010 is written as 1010b –Decimal 1010 is written as 1010 or 1010d

1.2 Data representation: Number systems (bases)  Number systems used –Binary: The internal representation inside the computer. They may be represented in binary, octal, or hexadecimal. –Decimal: The system people use.  ASCII representations of numbers used for I/O: –ASCII binary –ASCII octal –ASCII decimal –ASCII hexadecimal

1.2 Data representation: Number systems (bases) Example

A.1 Binary numbers : Addition & Multiplication  Binary multiplication *  Binary addition table

A.1 Binary numbers : Addition & Multiplication  Examples: b 1110b b * 1101b  b b b * 1111b

A.2 Hexadecimal numbers : Addition & Multiplication  Hex addition and multiplication tables are large  We can still do simple calculations by hand B852h 23Ah + 5A65h * 100h ABCh 2B3h + E F 0 h * 102h

A.3 Arithmetic: Converting to decimal  Binary to Decimal 1010b =1 * * * *10 0 =10  Hex to Decimal ABCh = 10 * * * 16 0 = 10 * * * 1 = = 2748

A.3 Arithmetic: Converting to decimal  Octal to Decimal 256o = 2 * * * 8 0 =174 Conclusion: (Number) n =  (multiply each digit by an integer power of n)

A.3 Arithmetic: Conversion problems  1234 base 5 or (1234) 5 =_________  b = ________  45677h = ________  736.4o = ________

A.3 Arithmetic: Conversion from decimal  Decimal integer to Binary 54 = 27 * = 13 * = 6 * remainder quotient 1 = 0 * = 1 * = 3 * 2 + 0

A.3 Arithmetic: Conversion from decimal  Decimal integer to Hex :  Decimal integer to octal 54 = 6 * = 0 * o 54= 3 * = 0 * h

 Decimal fraction to Binary (Octal, Hex) A.3 Arithmetic: Conversion from decimal ( ) 10 2X X X X = (0.1011) integer

A.3 Arithmetic: Conversion from decimal  Conclusion  a decimal integer to a base n representation  successive division by n  accumulation of the remainders  a decimal fraction to a base n representation  successive multiplication by n  accumulation of the integer digits

A.3 Arithmetic: Conversion problems  (1234) 10 =(________) 2  ( ) 10 =(________) 2  (1234) 10 =(________) 8  (1234) 10 =(________) 16

A.3 Arithmetic: Conversions: hex, octal and binary  Conversion between base 2 and base 8 = b = = 72o  Conversion between base 2 and base 16 = b = = 3Ah  Note: we often write binary numbers in hex: –binary numbers can be very long –it is easy to convert back and forth

A.3 Arithmetic: Conversion problems  Write ABCh in binary.  Write b in hex.  Write b in octal

A.3 Arithmetic: Comments  See appendix A for more information.  It is EXTREMELY important to get good at hex and binary –conversion –addition.

A.3 Arithmetic: Signed numbers  Signed numbers: The number of bits must be fixed. In every case, the highest bit is the sign bit.  0 means +  1 means -  Example:  Unsigned number: 1101b = 13  Signed number: 1101b = ?

A.3 Arithmetic: Two’s complement 1101 b (signed binary number) 0010 b (reverse all bits) b (unsigned value = 3) - 3d = One’s complement Two’s complement two’s complement of n = NOT(n) +1 reversible

A.3 Arithmetic: Practice problems  Find the 8 bit two’s complement representation of -2Ch  Find the 8 bit two’s complement representation of 2Ch  What is decimal representation of the two’s complement number ?

A.3 Arithmetic: Range of signed numbers  Two's complement: Sizes Signed byte: -128 to +127 = Signed word: -32,768 to +32,767 = Singed double word: -2,147,483,648 to +2,147,483,647 =  Comments: There is one more negative than positive value There are (about) half as many positive signed values as unsigned values

A.3 Arithmetic: Addition & Subtraction (signed)  Algorithm to add in signed decimal (sign and magnitude) If both numbers have the same sign Add the two magnitudes Prefix with the common sign else Subtract the number with smaller magnitude from the number with the larger magnitude Prefix with the sign of the number with the larger magnitude.

A.3 Arithmetic: Addition & Subtraction (signed) Two's complement: 1) add two numbers including their sign bits 2) discard any carry out of the sign position  Addition Example:

A.3 Arithmetic: Addition & Subtraction (signed) Example:  Subtraction 1) Take the 2’s complement of the subtrahend (including the sign bit) 2) Add it to the minuend (including the sign bit)

A.3 Arithmetic: Character Storage  Characters are stored as numbers  Coding schemes –ASCII (7 or 8 bit) –EBCDIC (8 bit) –Unicode (16 bit)  ASCII Examples: “A” = 65d = 41h “a” = 97d = 61h “B” = 66d = 42h “b” = 98d = 62h “0” = 48d = 30h “1” = 49d = 31h “ “ = 32d = 20h “*” = 42d = 2Ah

1.3 Introducing Assembly Language: MASM Installation  Insert CD in CD-Rom  Go to Desktop, select My Computer  Select CD-Rom directory (\IRVINE)  Double click “index.html”  On the new screen, follow the links, install MASM613, sample program, link library etc.

 Select Start | Programs (| Accessories) |MS-DOS (Command) Prompt  Type edit autoexec.bat  Add the following commands in the file: SET HELPFILES=c:\masm613\help\*.hlp PATH=c:\masm613\bin;c:\masm613\binr;%PATH%  Save and Exit edit  Type autoexec 1.3 Introducing Assembly Language: Setup System Environment

1.3 Introducing Assembly Language: A simple Debug program  MOV AX, 10 ADD AX, 20 SUB AX, 5 MOV [130], AX INT 20 Store 10 into register AX Terminate program  Assembler: converts programs from assembly language to machine language Store AX in memory location 130h

1.3 Introducing Assembly Language: Running a Debug program  Select Start | Programs (| Accessories) |MS-DOS (Command) Prompt  Type Debug  Type A 100, type the program, press return  Type R (registers) to display the registers  Type T (trace) as needed to step through program  Type G (go) to execute the rest of program  Type D to display locations 130 and 131  Type Q (quit) to exit Debug

1.3 Introducing Assembly Language: Debug register display Next instruction Contents of AX (hex)  -R AX=0030 BX=0000 CX=0000 SP=FFEE... DS=1FA6 ES=1FA6 SS=1FA6 CS= FA6:0106 2D0500 SUB AX, 0005

1.3 Introducing Assembly Language: Debug memory display Contents of locations 130 and 131. Namely 002Bh  -D FA6:0130 2B 00 Note:  The individual bytes in binary are reversed when stored in memory Example: would be stored in memory as

1.3 Introducing Assembly Language: Debug disassembly  -U 100 1FA6:0100 B81000 MOV AX, FA6: ADD AX, FA6:0106 2D0500 SUB AX, FA6:0109 A33001 MOV [0130],AX 1FA6:010C CD20 INT 20 1FA6:010E 1F POP DS Memory locations Machine code Disassembled assembly code

 CSCE 380  Department of Computer Science and Computer Engineering  Pacific Lutheran University  2/2/2000