1. Fundamental of Assembly Language Programming (for Microprocessor)
Prima Dewi Purnamasari
Microprocessor
Electrical Engineering Department
Universitas Indonesia

2. Computer Language High Level language Low Level Language Machine Codes
Pascal, C, C++, Java, etc
Low Level Language
Assembly
Machine Codes
 in binary
1234 FFAB 1234 H  in hexadecimal
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3. Why Assembly?
Assembly has several features that make it a good choice many some situations.
It's fast – Assembly programs are generally faster than programs created in higher level languages. Often, programmers write speed-essential functions in assembly.
It's powerful – You are given unlimited power over your assembly programs. Sometimes, higher level languages have restrictions that make implementing certain things difficult.
It's small – Assembly programs are often much smaller than programs written in other languages. This can be very useful if space is an issue.
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4. Preparation for Assembly Programming
Basically you will need:
Program editor  as simple as Notepad
Assembler
MASM 
TASM  Made by Borland, a commercial product
NASM 
Be careful in writing your programs, because it runs directly on your microprocessor!
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5. Steps to Create a Program
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6. MASM32
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7. TASM
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8. Emulator
an emulator is hardware and/or software that duplicates (or emulates) the functions of a first computer system in a different second computer system, so that the behavior of the second system closely resembles the behavior of the first system.
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9. Emu8086
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10. Individual Assignment
Download and install
emu8086 (trial)
Find corresponding tutorial on how to use it (available on the Internet!), self study!
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11. Group assignment
Each group is responsible to bring at minimum 1 laptop (with emu8086 installed) to class every session
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12. Creating an Assembly Language Program
An assembly language program should be written with any text editor and have the extension filename.asm.
The assembler and Linker
The assembler program converts a symbolic source module (file) into a hexadecimal object file
The linker program executes as the second part of ML, reads the object files, created by the assembler program, and links them into a single execution file (.EXE)
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14. Assembly Program Structure
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16. LIST File, generated automatically after program successfully assembled
MemoryAddress
Machine codes
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17. NEXT: MOV AX, [BX] ; comment
Writing Structure
NEXT: MOV AX, [BX] ; comment
1= label, followed by “:”
2= opcode
3= operand
4= comment, preceded with”;” 1 2 3 4
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18. Writing Structure
Each statement in an assembly language program consists of four parts or fields.
The leftmost field is called the label.
used to store a symbolic name for the memory location it represents
All labels must begin with a letter or one of the following special $, -, or ?.
a label may have any length from 1 to 35 characters
The label appears in a program to identify the name of a memory location for storing data and for other purposes.
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19. The next field to the right is the opcode field.
designed to hold the instruction, or opcode
the MOV part of the move data instruction is an example of an opcode
Right of the opcode field is the operand field.
contains information used by the opcode
the MOV AL,BL instruction has the opcode MOV and operands AL and BL
The comment field, the final field, contains a comment about the instruction(s).
comments always begin with a semicolon (;)
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20. Click “View” and look the changes in every menu list:
Try it in emulator!
Click “View” and look the changes in every menu list:
registers
Data
Screen
Flags
etc
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21. Computer Data Formats
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22. Computer Data Formats ASCII and Unicode Data
Binary Coded Decimal (BCD)
Byte-Sized Data
Word-Sized Data
Doubleword-Sized Data
Real Numbers
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23. ASCII Data
American Standard Code for Information Interchange (ASCII) data represent alphanumeric characters in the memory of a computer system (Table 1.7)
The standard ASCII code is a 7-bit code with the eighth and MSB used to hold parity in some systems
ASCII are most often stored in memory using a special directive to the assembler program called define byte(s) or DB
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25. BCD Data
Binary-Coded Decimal (BCD) information is stored in either packed or unpacked forms
Packed BCD data are stored as two digits per byte
Unpacked BCD data are stored as one digit per byte
The range of a BCD digit extends from to or 0-9 decimal
Table 1.9 shows some decimal numbers converted to both packed ad unpacked BCD
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27. Byte-Sized Data
Byte-size data are stored as unsigned and signed integers
Negative signed numbers are stored in the 2’s complement form
Whenever a number is 2’s complement, its sign changes from negative to positive or positive to negative
See example 1-22, 1-23
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29. Define bit (DB) directive is used to store 8-bit data in memory
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30. Word-sized Data A word (16-bits) is formed with two bytes of data
The LSB is always stored in the lowest-numbered memory location, the MSB in the highest (i.e., little endian format)— used with Intel family of microprocessor
An alternate method (i.e., big endian format) is used with the Motorola family of micro-processors
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31. Word-sized Data
Fig 1.11(a) & (b) shows the weight of each bit position in a word of data
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33. Example 1.25 shows several signed and unsigned word-sized data stored in memory using the assembler program
Note that define word(s) directive or DW causes the assembler to store words in the memory
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35. Doubleword-sized Data
Doubleword-sized data requires four bytes of memory (32-bit number)
Doubleword-sized data appear as a product after a multiplication and also as a dividend before a division
Fig shows the form used to store doublewords in the memory and the binary weights of each bit position
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37. To define doubleword-sized data, use assembler directive define doubleword or DD
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38. Real Numbers
A real number (floating-point number) contains two parts: a mantissa, significant, or fraction and an exponent
Fig and example 1-27 depicts both the 4-byte (single precision) and 8-byte (double precision) forms of real numbers
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40. The exponent is stored as a biased exponent
an exponent of 23 is represented as a biased exponent of or 130 (82H) in the single- precision form or as 1026 (402H) in the double-precision form
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42. Assembler detail From chapter 4 42
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43. Directives
Indicate how an operand or section of program is to be processed by the assembler
Storing Data in a Memory Segment: DB, DW, DD, SEGMENT, .DATA, ENDS, DUP, ALIGN e.g.: Example 4.12
THIS refers the data as byte or word
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44. Memory is reserved for use in the future by using a question mark (
Memory is reserved for use in the future by using a question mark (?) as an operand for a DB, DW, or DD directive.
when ? is used in place of a numeric or ASCII value, the assembler sets aside a location and does not initialize it to any specific value
DUP: creates array with or without initial values
It is important that word-sized data are placed at word boundaries and doubleword-sized data are placed at doubleword boundaries.
if not, the microprocessor spends additional time accessing these data types
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46. EQU, ORG ASSUME
Equate directive (EQU) equates a numeric, ASCII, or label to another label.
equates make a program clearer and simplify debugging
EX: TEN EQU 10 ….
MOV AL,TEN
The ORG (origin) statement changes the starting offset address of the data or code segments.
At times, the origin of data or the code must be assigned to an absolute offset address with the ORG statement.
ASSUME tells the assembler what names have been chosen for the code, data, extra, and stack segments.
Used only with full-segment definition
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48. PROC and ENDP Indicate start and end of a procedure (subroutine).
they force structure because the procedure is clearly defined
Both the PROC and ENDP directives require a label to indicate the name of the procedure.
RET instruction executed the end of the proc.
USES directive indicates which registers are used by the proc.
The assembler automatically save and restore them using the stack instructions.
EX: PRC1 PROC USES AX BX CX
Use .LISTALL directive to view all instruction generated by assembler
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51. The assembler uses two basic formats for developing software:
Memory Organization
The assembler uses two basic formats for developing software:
one method uses models; the other uses full-segment definitions
Memory models are unique to MASM.
The models are easier to use for simple tasks.
The full-segment definitions offer better control over the assembly language task and are recommended for complex programs.
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52. Models
There are many models available to the MASM assembler, ranging from tiny to huge.
.MODEL memsize
TINY: all software and data fit into 64kb memory segment. Useful for small programs. assembled as a command (.COM) program
SMALL: one data segment with one code segment for a total of 128kb of memory. assembled as an execute (.EXE) program
Start of segments: .CODE, .DATA, .STACK
Start of instructions and load segment registers with segment addresses: .STARTUP
Exit to DOS: .EXIT
End of file: END
MP selection : .386, .486, .586,
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54. Full Segment Definitions
Full-segment definitions are also used with the Borland and Microsoft C/C++ environments for procedures developed in assembly language
More structured form than the model method
Use assume directive before the program begins.
The program loader does not automatically initialize DS and ES. These registers must be loaded in the program
STACK_SEG, DAT_SEG, CODE_SEG, END MAIN
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STACK_SEG SEGMENT ‘STACK’
DW 100H DUP(?)
STACK_SEG ENDS
DATA_SEG SEGMENT ‘DATA’
LISTA DB 100 DUP(?)
LISTB DB 100 DUP(?)
DATA_SEG ENDS
COSE_SEG SEGMENT ‘CODE’
ASSUME CS:CODE_SEG, DS:DATA_SEG, SS:STACK_SEG
MAIN PROC FAR
MOV AX, DATA_SEG
MOV ES, AX
MOV DS, AX
CLD
MOV SI, OFFSET LISTA
MOV DI, OFFSET LISTB
MOV CX, 100
REP MOVSB
MAIN ENDP
CODE_SEG ENDS
END MAIN
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56. Introduction to MOV Instruction
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57. Data Addressing Modes
opcode
an opcode, or operation code, tells the microprocessor which operation to perform
MOV instruction provides a basis for explanation of data-addressing modes
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58. MOV Instruction
MOV instruction perform COPY of a value, either from or to memory or register
MOV = COPY
MOV ≠ MOVE
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59. MOV BX, CX
The source register’s contents do not change. the destination register’s contents do change
The contents of the destination register or destination memory location change for all instructions except the CMP and TEST instructions.
Note that only the rightmost 16 bits of register EBX change. The MOV BX, CX instruction does not affect the leftmost 16 bits of register EBX
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60. Some MOV Variant MOV AX,BX MOV [BX], AX MOV DATA,AX MOV AX,0123H
[ ] sign represents memory location
Destination = memory which has address as in BX
MOV DATA,AX
DATA is a name the programmer define in DATA SEGMENT
destination=memory named DATA
MOV AX,0123H
a value 0123H is copied to AX register
There are several more, but the above are the fundamental ones
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61. Rules in addressing. DO NOT:
Mix different size of register
MOV AX, BL
Perform memory to memory addressing
MOV [1234H],DATA
Copy content of one segment register to another
MOV DS,ES
Use CS as the destination register
MOV CS,1000H
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62. Group Assignment—Due Thursday 22/9
Make a program (altogether in one program, sequentially)
Reserve place for data in data segment namely DATA1 with type word
Copy 1234 to AX
Copy 0011B to AL
Copy 12H to AH
Copy AX to DATA1
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63. The report Write the program in emulator Compile it.
Run the program in emulator. (single step). Analyze the effect on the registers and memory for each line of code
Written report should be made as comprehensive as it can be (greater score for better report)
The main part of your report would be:
Print of program (source code), provide sufficient comment
Print of LISTING file
Program analysis
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