1. ASSEMBLY LANGUAGE
T S Pradeep Kumar
VIT University – Chennai Campus
http://www.pradeepkumar.org

2. Topics
• CPU Behavior
• Accumulator Based CPU
• Assembly language
• Pros and Cons of Assembly Language
• Elements of Assembly Language
• Example: AC = AC x N
• Greatest Common Divisor
• Macros and Subroutines

3. CPU Behavior

5. Accumulator based CPU
• All the arithmetic calculations happens at the Accumulator
register
• Instructions are fetched by the program control Unit
(PCU).
• They are executed in Data processing Unit (DPU)
• Instruction are typically look like this
• X1 = fi (X1, X2)
• X1, X2 denotes a CPU register (AC, DR, or PC) or an
external memory location M (address)

6. Accumulator based CPU
• fi is operation performed by the ALU are limited to Fixed
point addition, subtraction, shifting and logical operations.

7. Assembly Language
• An assembly language is a symbolic representation of the
machine language of a specific processor, augmented by
additional types of statements that facilitate program
writing and that provide instructions to the assembler
• An assembler is a program that translates assembly
language into machine code.
• Assembly Language is hardware dependent with a
different assembly language for each type of processor.

8. Advantages of Assembly Language over
HLL
• Debugging and Verification
• Making compilers
• Embedded systems
• Hardware drivers and system code
• Accessing instructions that are not accessible from HLL
• Self modifying code
• Optimizing code for size and speed
• Function libraries

9. Disadvantages of Assembly language
• Development time
• Reliability and security
• Debugging and verifying is difficult
• Maintainability
• Portability
• Compilers have been improved a lot in recent years

10. Assembly language elements
• Label
• Mnemonic
• Operands
• Comment

11. Example: AC = AC x N
Label Mnemonic, operands Comments
One 00…001 The constant one
Multi N The multiplier
Ac 00...000 Location for initial value of Y in AC
Prod 00…000 Location for partial product P
ST ac Save initial value of Y of AC
Loop LD mult Load N into AC to test for termination
BZ exit Exit if N=0; otherwise continue
LD one Load 1 into AC
MOV DR, AC Move 1 from AC to DR
LD mult Load N into AC to decrement it
SUB Subtract 1 from N
ST mult Store decremented N
LD ac Load initial value Y of AC
MOV DR, AC Move Y from AC to DR

12. Continued…
Label Mnemonic, operands comments
LD prod Load current partial product P
ADD Add Y to P
ST prod Store the new partial product P
BR loop Branch to Loop
Exit …..

13. Example - GCD

14. Example - GCD

15. Macros and Subroutines
• Macros and subroutines are useful for the simplification of
program
• Group of instructions to be treated as a single entities
• Name MACRO Operand,…
………}
ENDM
• Macros are helpful in creating new opcode names
• Introduce new data types and addressing modes

16. Macros
• Example of MACRO
• LDAI MACRO ADR
LDHL ADR
MOV A,M
ENDM
Later,
LDAI 1000H
becomes a separate instruction

17. Subroutines
• Also called as procedure
• A subroutine definition is assembled into object code
• Two executable instructions
• CALL or JUMP TO SUBROUTINE
• RETURN
CALL SUB1
NEXT …..
…...
SUB1 ……
……
RETURN

18. Subroutines

19. EVALUATION……