CPE 408330� Assembly Language and�Microprocessors��Chapter 7: Assembly Language �Program Development with MASM�������

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[Computer Engineering Department,

Hashemite University, © 2008]

Lecture Outline

• 7.1 Statement Syntax for a Source Program
• 7.2 Assembler Directives
• 7.3 Creating a Source File with an Editor
• 7.4 Assembling and Linking Programs
• 7.5 Loading and Executing a Run Module

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7.1 Statement Syntax for a Source�Program

􀂄 Assembly language statement syntax

􀂄 Directive statement syntax

􀂄 Constants in a statement

􀂄 Operand expressions using the arithmetic, relational, and logical operators

􀂄 Value-returning and attribute operators

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7.1 Statement Syntax for a Source�Program

• The source program is a series of assembly language and directive statements that solves a specific problem.
• The assembly language statements tell the microprocessor the operations to be performed, and
• The directive statements instruct the assembler program on how the program is to be assembled.
• Syntax: the rules that must be used when writing assembly language and directive statements for MASM.

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7.1 Statement Syntax for a Source�Program

􀂄 Assembly language statement syntax:

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LABEL: OPCODE OPERAND(S) ;COMMENT(S)

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• EXAMPLES:

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START: MOV CX, 10 ;Load a count of 10 into register CX

MOV CX, 10 ;Initialize the count in CX

CLC ;Clear the carry flag

*. Leave one blank space between fields and one space before the opcode if no label is used.

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7.1 Statement Syntax for a Source�Program

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Symbols used for specifying register operands

􀂄 Assembly language statement syntax

7.1 Statement Syntax for a Source Program

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􀂄 Assembly language statement syntax

7.1 Statement Syntax for a Source�Program

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􀂄 Directive statement syntax:

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LABEL: DIRECTIVE OPERAND(S) ; COMMENT (S)

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EXAMPLES:

DB FFH ; Allocate a byte location initialized to FFH

DB FFH, FFH, FFH, FFH, FFH ; load next 5 bytes

(DB stands for Define Bytes)

• DB: causes the next byte location in memory to be loaded with the given value.
• DB: used to initialize memory locations with data.

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7.1 Statement Syntax for a Source�Program

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􀂄 Constants in a statement

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􀂙 Constants in an instruction or directives can be expressed in any of many data types such binary, decimal, hexadecimal, octal, and character data types.

􀂙 The first digit of a hexadecimal number must be one of the numbers in the range 0 through 9.

􀂙 Typically, data and addresses are expressed in hexadecimal form, and the count for shift, rotate, and string instructions in commonly expressed in decimal form.

􀂙2’s complement of the number must be used for negative numbers expressed in binary, hexadecimal, or octal form.

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7.1 Statement Syntax for a Source�Program

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􀂄 Constants in a statement

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• Can use Decimal
• Mov AL, 10 or Mov AL, 10D. Use Neg: Mov AL, -10
• Can use Hex
• Mov AL, 10H
• Can use Binary
• Mov AL, 10B
• Can use Octal
• Mov AL, 10Q
• Can use Char
• Mov AL, “A”

7.1 Statement Syntax for a Source�Program

• EXAMPLE

The repeat count in CX for a string instruction is to be equal to decimal 255. Assume that the instruction that is to load the count has the form

MOV CX, XX

where XX stands for the count, an immediate operand that is to be loaded into CX. Show how the instruction should be written.

• Solution:

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MOV CX, 255D

or MOV CX, 255

or MOV CX, 0FFH

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7.1 Statement Syntax for a Source�Program

• EXAMPLE

The count in a move instruction that is to load CX is to be -10. Write the instruction and express the immediate operand in binary form.

• Solution:

The binary form of 1010 is 010102. Forming the 2’s complement by complementing each bit and adding 1, we get

10101

+1

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10110

Therefore, the instruction is written as

MOV CX, 10110B

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7.1 Statement Syntax for a Source�Program - Expressions

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• Expression: group of several arithmetic, logical and relational operations
• Arithmetic : +,-,*,/,%,shifts
• Logical: NOT,AND,OR,XOR
• Relational: testing conditions,returns true, false
• We can use an expression rather than a straight operand i.e.
• Mov AL, A / B , where A and B are variables
• The next tables list all the operators that can be used in an expression.
• Examples: *, /, MOD, SHL, SHR, +, -, EQ, NE, LT, GT, LE, GE, NOT, AND, OR, XOR
• Parentheses can be used to change order of execution i.e. MOV AL, (A+B)/5

7.1 Statement Syntax for a Source�Program - Expressions

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7.1 Statement Syntax for a Source�Program - Expressions

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7.1 Statement Syntax for a Source�Program - Expressions

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7.1 Statement Syntax for a Source�Program - Expressions

• EXAMPLE

Find the value the assembler assigns to the source operand for the instruction

MOV BH, ( A * 4 – 2 ) / ( B – 3 )

for A=8 and B=5.

• Solution:

The solution is calculated as

(8*4-2)/(5-3) = (32 – 2)/(2)

= (30)/(2) = 15

And using hexadecimal notation, we get the instruction

MOV BH, 0FH

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7.1 Statement Syntax for a Source�Program - Expressions

• EXAMPLE

What value is used for the source operand in the expression

MOV AX, A LE (B – C)

if A=234, B=345, and C=111?

• Solution:

Substituting into the expression, we get

234 LE (345 – 111)

234 LE 234

since the relational operator is satisfied, the instruction is

equivalent to

MOV AX, 0FFFFH

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7.1 Statement Syntax for a Source�Program

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􀂄 Value-returning and attribute operators:

• Operators used to return information about the operand rather than the operand itself or to change the attributes of the operand before it is fed to the instruction.
• The next tables give us a list: Value-Returning

- SEG A, Offset A, TYPE A (B, W, Far or Near), SIZE A and Length A

• Attribute:

- PTR (override the TYPE), DS: ES: SS, SHORT, THIS, HIGH and LOW

7.1 Statement Syntax for a Source�Program

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7.1 Statement Syntax for a Source�Program

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7.2 Assembler Directives

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7.2 Assembler Directives

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􀂄 Data directives

􀂄 Segment-control directives

􀂄 Modular programming directives

􀂄 Directives for memory usage control

􀂄 Directives for program listing control

7.2 Assembler Directives

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Duplicate the values in ( ) a number of times

7.2 Assembler Directives

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7.2 Assembler Directives

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􀂄 Segment-control directives

􀂙Three kinds of memory segment:

• Code segment

• Data segment

• Stack segment

􀂙The segment-control directives partitions and assigns a source program to a specific memory segment.

􀂙The beginning of a segment is identified by the segment (SEGMENT) directive and its end is

marked by the end of segment (ENDS) directive.

7.2 Assembler Directives

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7.2 Assembler Directives

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Name of the segment

Paragraph (align-type):

- Sets the boundaries (here it is 16 byte)

- Can also be Byte, Word or Page

Combine-type attribute:

Specifies that this along with other

segments that have the same

name should be concatenated to

generate one physical Seg. Can also

be: Common (overlap), AT (specific)

Stack (part of the stack) or Memory

(Above all defined seg)

Class attribute, tells that this

is a code seg. Other values

are: Data, Stack

Tells which register

holds the base address

of the Seg

7.2 Assembler Directives

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7.2 Assembler Directives

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7.2 Assembler Directives

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7.2 Assembler Directives

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7.2 Assembler Directives

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7.2 Assembler Directives

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􀂄 Modular programming directives

􀂙Two kinds of procedures:

• Near procedure - IP in stack when called

• Far procedure - IP and CS in stack when called

􀂙NEAR is assumed as the default attribute of a

procedure.

􀂙If a procedure can be called from other modules,

its name must be made public by using the

PUBLIC directive.

􀂙If a procedure in another module is to be called

from the current module, its name must be

declared external by using the EXTRN directive.

7.2 Assembler Directives

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7.2 Assembler Directives

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7.2 Assembler Directives

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7.2 Assembler Directives

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􀂄 Examples of a source program using directives

7.2 Assembler Directives

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􀂄 Examples of a source program using directives

7.3 Creating a Source File with an�Editor

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C:\_

EDIT A:BLOCK.SRC [↵]

Type the program line by line

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MOV AX, DATASEGADDR

MOV DS, AX

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etc.

Alt-F

Menu to save or print the file

NEW

OPEN

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etc.

Loaded file not saved. Save it now

<Yes> <No> <Cancel> <Help>

[↵]

X [↵]

7.4 Assembling and Linking Programs

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7.4 Assembling and Linking Programs

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􀂄 Source listing

Original

source code

Machine

Code

Program

starting

address

7.4 Assembling and Linking Programs

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􀂄 Source listing

Symbol

table

Errors and warnings are reported here

Segments created

7.4 Assembling and Linking Programs

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􀂄 Link program and modular programming

7.4 Assembling and Linking Programs

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􀂄Benefits of modular programming:

• Programmers can be working on a software project simultaneously.
• Smaller sizes of the modules require less time to edit and assemble.
• Modular programming makes it easier to reuse old software.

7.4 Assembling and Linking Programs

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􀂄 Initiating the assembly and linking processes

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ML [OPTIONS] file name [[OPTIONS] file name] … [/link link-options]

ML /Fl /Fm BLOCK.ASM (↵)

Display sequences for initiating assembly of a program

7.4 Assembling and Linking Programs

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􀂄 Initiating the assembly and linking processes

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LINK (↵)

Display sequences to initiate linking of object files

7.5 Loading and Executing a Run�Module

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7.5 Loading and Executing a Run�Module

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• Solve the following problems from Chapter 7 from the course textbook:

3, 21, 39, 42, 50

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H.W. #7