Computer Architecture CST 250 Assembly Language Prepared by

Computer Architecture CST 250 Assembly Language Prepared by: Omar Hirzallah

Contents • Assembly Language • Instruction Types • Introduction to Programming With Assembly

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.

Instructions • Syntax of assembly language • 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

Instructions • Syntax of assembly language • Operation [operand] , [operand/number] Examples: instruction Explanation mov dh, 00000101 b Put 5 in dh register dh=5 add ax, 00001111 b add the 15 into ax. The result will be in ax register ax=ax+15

Instructions Examples: instruction 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

Instructions Examples: instruction 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

Instructions Examples: instruction 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

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

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

Instruction types 1. 2. 3. 4. 5. Data transfer instructions: They move data from one register/memory location to another. Arithmetic instructions: They perform arithmetical operations. Logical instructions: They perform logical operations. Control transfer instructions: They modify the program execution sequence. Input/output (I/O) instructions: They transfer information between external peripherals and system components ( CPU/Memory) 6. Processor control instructions: They control processor operation.

Example of : Arithmetic instruction Add register 1, register 2 Flags ALU Operation [ A ]

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

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

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 and CL, 01101001 b CL x x x x and 0 1 1 0 0 1 CL 0 x x 0 0 x

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 Or CL, 10010110 b CL x x x x OR 1 0 0 1 1 0 CL 1 x x 1 1 x

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 xor CL, 10010110 b CL x x x x XOR 1 0 0 1 1 0 CL x x x x