Download Laboratory Work No 05 Syntax of Assembly

Laboratory Work No 05
Syntax of Assembly
Objectives:
In this experiment you will learn:
1. Format of instructions and macroinstructions.
2. Syntax of operands in Assembly.
3. Syntax of operators in Assembly.
Pre Lab Work
Part I
1. Review the material related to Syntax of Assembly (assLect5):
. Basic Elements of Assembly Language



Microsoft syntax notation
o Elements within square brackets [ ] are optional
o Elements within { …| …|…} requires a choice of the enclosed elements
o Elements in italics denote items which have known definitions or descriptions
o Example: [{+ | -}] digits [radix]
Integer constants (integer literal)
o Syntax: [{+ | -}] digits [radix]
o Optional leading + or – sign
o binary, decimal, hexadecimal, or octal digits
o Common radix characters:
 h – hexadecimal
 d – decimal
 b – binary
 r – encoded real
o Examples: 30d, 6Ah, 42, 1101b
o Hexadecimal beginning with letter must have leading 0: 0A5h
o If no radix is given, the integer constant is assumed to be decimal
Integer expressions
o A mathematical expression involving integer value and arithmetic operators
o Operators and precedence levels:
o

Examples:
12 – 1 MOD 5, -3 + 4 *6 - 1
Real Number Constants
o
Syntax: [sign] integer.[integer][exponent]
sign
{+ | -}
exponent




E[{+ | -}]integer
o Examples: 2., +3.0, -44.26E+05, 26.E-5
o Note: At the very least, there must be a digital or a decimal point
Character and String Constants
o Enclose character in single or double quotes
 'A', "x"
 ASCII character = 1 byte
o Enclose strings in single or double quotes
 "ABC"
 'xyz'
 Each character occupies a single byte
o Embedded quotes: 'Say "Goodnight," Gracie'
Reserved Words and Identifiers
o Reserved words cannot be used as identifiers
 Instruction mnemonics, directives, type attributes, operators, predefined symbols
 See MASM reference in Appendix A
o Identifiers – a programmer-choice name
 1-247 characters, including digits
 not case sensitive
 first character must be a letter, _, @, ?, or $
Directives
o Commands that are recognized and acted upon by the assembler
 Not part of the Intel instruction set
 Used to declare code, data areas, select memory model, declare procedures, etc.
 not case sensitive
o Different assemblers have different directives
 NASM not the same as MASM
 See MASM reference in Appendix D
Instructions
o Assembled into machine code by assembler
o Executed at runtime by the CPU
o We use the Intel IA-32 instruction set
o An instruction contains:
 Labels (optional)

Act as place markers

marks the address (offset) of code and data

Follow identifier rules

Data label
- must be unique
- example: myArray (not followed by colon)

Code label
- target of jump and loop instructions
- example: L1:



(followed by colon)
Mnemonics (required)

Instruction Mnemonics

memory aid

examples: MOV, ADD, SUB, MUL, INC, DEC
Operands (depends on the instruction)

constant

constant expression

register

memory (data label)

Constants and constant expressions are often called immediate values
Comments (optional)

Comments are good!
- explain the program's purpose
- when it was written, and by whom
- revision information
- tricky coding techniques
- application-specific explanations

Single-line comments
- begin with semicolon (;)

Multi-line comments
- begin with COMMENT directive and a programmer-chosen character
- end with the same programmer-chosen character
- Example: COMMENT &
This is a comment.
This line is also a comment.
& This line is also a comment.
o
Instruction Format Examples
 No operands
stc

; set Carry flag
One operand
inc eax
; register
inc myByte
; memory

Two operands
add ebx,ecx
; register, register
sub myByte,25
; memory, constant
add eax,36 * 25
; register, constant-expression
Lab Work
Part I
1.UseTASM for analyzing elements of Assembly syntax:
For example for MOV Instruction
It copies the second operand (source) to the first operand (destination). The source operand
can be an immediate value, general-purpose register or memory location. The destination register
can be a general-purpose register, or memory location. Both operands must be the same size,
which can be a byte or a word. These types of operands are supported:
MOV REG, memory
MOV memory, REG
MOV REG, REG
MOV memory, immediate
MOV REG, immediate
For segment registers only these types of MOV are supported:
MOV SREG, memory
MOV memory, SREG
MOV REG, SREG
MOV SREG, REG
NOTE:
The MOV instruction cannot be used to set the value of the CS and IP registers. Here is a short
program that demonstrates the use of MOV instruction:
MOV AX, 0B800h ; set AX to hexadecimal value of B800h.
MOV DS, AX ; copy value of AX to DS.
MOV CL, 'A' ; set CL to ASCII code of 'A', it is 41h.
MOV CH, 1101_1111b ; set CH to binary value.
MOV BX, 15Eh ; set BX to 15Eh.
MOV [BX], CX ; copy contents of CX to memory at B800:015E
Instruction RET ; returns to operating system.
2.UseTASM for analyzing elements of Assembly operators syntax: Arithmetic operators,
Shift operators, Index operator [ ] , Operator of segment redeclaration ’:’ (colon), Operator of
obtaining offset of expression offset, Operator of redeclaration (redefinition) of the ptr.
Make comment for sentences with these operands and operators.