1. Chapter 3
Machine Language
and
Assembly Language

2. Generation of programming language.

3. Machine Language
Consisting of strings of 1’s and 0’s and stored as binary numbers.
Also known as machine code or object code.
To solve this problem; mnemonics (Assembly language).

4. Fields In Machine Language
Contain of two fields:
Operation code (Op-Code)
What operation must done by processor
Operand
Contain of memory address or data address.

5. Assembly Language
Is a symbolic representation of machine code (mnemonic).
Easy to programmer.
To write a program, a programmer must know how many register and internal structure of CPU.

6. Relationship between machine and assembly language

7. Advantages & Disadvantages of Machine Language
Efficient - making optimum use of both computer memory and processing time.
Do not use any translator.
Disadvantages
Difficult to write, read and understand.
Easy to make a mistake.

8. Advantages & Disadvantages of Assembly Language
Easy to write, read and understand.
Disadvantages
Must be translated into machine code by a separate program called an assembler.

9. Why Use Assembly Language?
Low level control
When you need to change the flags, or the control registers of the processor, as when entering protected mode.
Speed
Programs written in machine language execute fast!. It can execute times the speed of BASIC, and about twice as fast as a program written in C or Pascal.

10. Why Use Assembly Language?…
Time critical code
Critical sections of programs written in higher level languages can be written in assembly to speed up sections.
Small program size.
When you write a TSR for example this is very useful. Writing interrupt handlers is where assembly language shines.
Assembly language is very flexible and powerful; anything that the hardware of the computer is capable of doing can be done in assembly.

11. Three type of instruction
Executable statements
Assembler Directives (Pseudo-Instruction)
Macro Instruction

12. 1. Executable statements
One of the processor’s valid instructions which can be translated into machine code by the assembler
Example:
MOVE ADD ADDA
ADDI CMP SUB
MOVE.L #4, D2
;Tells the CPU to put the value of 4 in register 2.

13. 2. Assembler Directives (Pseudo-Instruction)
Assembler directives cannot be translated into machine code; they simply tell the assembler things it needs to know about the program and its environment.
Link symbolic names to actual values.
Set up predefined constants.
Allocate storage for memory.
Control the assembly process.

14. Example of Assembler Directives
Mostly the same as for our generic CPU, but with the size specify (.B, .W or .L) added for DC & DS

15. 3. Macro Instruction
A macro instruction is a program which are codified only once and can be used as many times as necessary.
Macro instruction is a module with specific function which can be used by different programs.
It’s very useful for the programmer in writing program (Do not write many times).
It is found in many other high-level languages, such as C.

16. Assembly language format
Contain of 4 fields
[Label:] Op Code [Operand/s] [;Comments]
The symbol [ ] is optional
Every field must at least 1 blank space.

17. Label
It is an optional field. If this field is exist, so it must start in first column.
Although there is no limit on length for this field but the assembler just consider only 8 characters to be significant.
The characters can be
Letter (a-z, A-Z)
Digits (0-9)
Special characters like $(dollar), .(dot) and _(underscore)

18. Label… Cannot put blank space in the label.
It cannot begin with a digit.
The assembler is not a case-sensitive
Eg: Value1 and value1 is same
Exercise: X, 4DATA, ORG, .Value1

19. Op Code Sometime it also call as ‘pseudo op’.
This field is in mnemonics form.
This is important field – (must have).
The assembler will translated the mnemonics to machine code.
Eg: MOVE, ADD, SUB, BNE
If this field contain of assembler directive it will not translated to machine code.
Eg: ORG, END, DC, DS

20. Operand/s The operand will use the data that can be executed.
General format: <source>,<destination>
The statement can be 0,1 or 2 operand.
When two or more operand subfields appear within a statement, they must be separated by a comma.
Eg: ADD.L D1,D2 2 operand
CLR.B D4 1 operand
RTS 0 operand

21. Comment The comment start with symbol (;).
The assembler will ignore after this symbol.
Example:
MOVE.L #4,D3; Move the value (4) of data to register 3
; all this line is a comment.

22. Reference Language level Finaly the real CPU
Level of programming languages
Macro Instruction