1. Computer Architecture CST 250
Assembly Language
Prepared by:Omar Hirzallah

2. Contents Assembly Language Instruction Types
Introduction to Programming With Assembly

3. Assembly Language 
An assembly language is a low-level programming language for a computer,microcontroller, or other programmable device, in which each statement corresponds to a single machine code instruction. Each assembly language is specific to a particular computer architecture, in contrast to most high-level programming languages, which are generally portable across multiple systems.

4. Instructions Syntax of assembly language Examples:
Operation [operand] , [operand/number]
Examples:
instruction
Explanation
mov ah, 25
Put 25 in ah register  dh=25
inc dx
increase the value of dx by  dx=dx+1
add ax, bx
add the contents of bx into ax. The result will be in ax register  ax=ax+bx
sub cx, bx
subtract the contents of bx from cx. The result will be in cx register  cx=cx-bx

5. Instructions Syntax of assembly language Examples:
Operation [operand] , [operand/number]
Examples:
instruction
Explanation
mov dh, b
Put 5 in dh register  dh=5
add ax, b
add the 15 into ax. The result will be in ax register  ax=ax+15

6. Instructions Examples: Decrease the value of dx by 1  dx=dx-1
Explanation
dec dx
Decrease the value of dx by 1  dx=dx-1
and ax, bx
Do logical AND for ax with bx. The result will be in ax register  ax=ax && bx
xor cx, bx
Do logical XOR for bx with cx. The result will be in cx register  cx=cx ^ bx
Mov ah, [x]
Put the content of the memory variable x in ah  ah=x
hlt
Stop the processor

7. Instructions Examples: Shift all bits of dx (1 position) to the right
Explanation
shr dx,1
Shift all bits of dx (1 position) to the right
 dx=dx/2
shr dx, 2
Shift all bits of dx (2 position) to the right
 dx=dx/4
shr dx, 3
Shift all bits of dx (3 position) to the right
 dx=dx/8
shr dx, 4
Shift all bits of dx (4 position) to the right
 dx=dx/16
shr dx, 5
Shift all bits of dx (5 position) to the right
 dx=dx/32

8. Instructions Examples: Shift all bits of dx (1 position) to the left
Explanation
shl dx,1
Shift all bits of dx (1 position) to the left
 dx=dx * 2
shl dx, 2
Shift all bits of dx (2 position) to the left
 dx=dx * 4
shl dx, 3
Shift all bits of dx (3 position) to the left
 dx=dx * 8
shl dx, 4
Shift all bits of dx (4 position) to the left
 dx=dx *16
shl dx, 5
Shift all bits of dx (5 position) to the left
 dx=dx * 32

9. Instructions Examples: JUMP (Loops and if statements )
There are two : Conditional and Unconditional
Instruction
Explanation
Cmp dx,1
je lable1
cmp means compare
Je means jump if equal
If(dx==1)
Do the instruction in front of lable1
mov dx, 1
dec dx
cmp dx, 0
je xyz
add dx,5
xyz: inc dx ..
If (dx != 0) {
dx=dx-1;
dx=dx+5 }
dx=dx+1

10. ALU Operation Examples: JUMP (Loops and if statements ) Instruction
Cmp dx,1 je
jne jl
jle jg
jge
Instruction
jmp
Unconditional jump used at any time without CMP Instruction
Conditional jump are used after CMP Instruction

11. Instruction types Data transfer instructions:
They move data from one register/memory location to another.
2. Arithmetic instructions:
They perform arithmetical operations.
3. Logical instructions:
They perform logical operations.
4. Control transfer instructions:
They modify the program execution sequence.
5. Input/output (I/O) instructions:
They transfer information between external peripherals and system components ( CPU/Memory)
Processor control instructions:
They control processor operation.

12. Example of : Arithmetic instruction
Add register1, register2
Flags
ALU Operation [ A ]

13. Examples
What will be the value of DX register after executing the following assembly code
mov DX, 12
shl DX, 1
Add DX, 5
Mov CX, 40
Shr CX, 2
Add DX,CX

14. Examples How many times the following code block will execute
mov DX, 12
XYZ:
Sub DX, 02
Add DX, 04
Mov CX, 34
And BX, 03
Xor DX, DX
Cmp DX, 0
je XYZ

15. Examples
Write the assembly instruction that clears bit # 1,2,4,7 of CL Register
Solution
clear means make the bit value is 0
Remember
X . 1 = X
X . 0 = 0 CL x
and 1 CL x
and CL, b

16. Examples
Write the assembly instruction that sets bit # 1,2,4,7 of CL Register
Solution
Set means make the bit value is 1
Remember
X + 1 = 1
X + 0 = X CL x OR 1 CL 1 x
Or CL, b

17. Examples
Write the assembly instruction that changes bit # 1,2,4,7 of CL Register
Solution
Change means if value is 0 make it 1 and if value is 1 make it 0
Remember
X + 1 = X’
X + 0 = X CL x
XOR 1 CL x
xor CL, b