Lab 3LEA INSTRUCTION, JMP, CMP, CONDITIONAL JUMP, LOOP

LEA Instruction LEA

Unconditional Jumps – JMP Instruction

JMP destination_lable

LABEL1:

Conditional Jumps – Signed Jumps

Symbol Description Condition JG / JNLE jump if grater than

jump if not less than or equalZF = 0 & SF = OF

JGE / JNL jump if grater than or equaljump if not less than

SF = OF

JL / JNGE jump if less thanjump if not greater than or equal

SF <> OF

JLE / JNG jump if less than or equaljump if not grater than

ZF = 1 or SF <> OF

Conditional Jumps – Unsigned Jumps

Symbol Description Condition

JA / JNBE jump if abovejump if not below or equal

CF = 0 & ZF = 0

JAE / JNB jump if above or equaljump if not below

CF = 0

JLB/ JNAE jump if belowjump if not above or equal

CF = 1

JBE / JNA jump if below or equaljump if not above

CF = 1 or ZF = 1

Conditional Jumps – Single Flag Jumps

Symbol Description ConditionJE / JZ jump if equal/ jump if equal to 0 ZF = 1JNE / JNZ jump if not equal/ jump if not 0 ZF = 0 JC jump if carry CF = 1JNC jump if no carry CF = 0JO jump if overflow OF = 1JNO jump if no overflow OF = 0JS jump if sign negative SF = 1 JNS jump if nonnegative sign SF = 0JP / JPE jump if parity even PF = 1JNP / JPO jump if parity odd PF = 0

CMP InstructionCMP destination, source

Just like SUB but the destination does not change.

Changes the Flags

Used with conditional jumps

Example – IF, THEN, ELSE•Suppose AL and BL contain extended ASCII characters, Display the one that comes first in the character sequence

Example – AND condition Read a character, and if it’s an uppercase letter, Accept it

Example – OR Condition•Read a character. If it’s 'y' or 'Y', display it; otherwise, terminate the program.

LOOP InstructionLOOP destination_Label

Display a row of 80 stars

Example – While Loop Count number of characters entered and terminate if carriage return is entered.

Example – Repeat Loop Read characters until a blank is read terminate.

Exercises Read characters from user and count the number of characters if they reached 30 display a message “The Program Cannot Accept anymore characters.”

org 100h MOV AH,1 ;PREPARE function TO read MOV CL,0 ;clear the register to count GO_TOP: INT 21H ;execute function INC CL ;increment to count the number of characters entered CMP CL,30 ;compare if CL equals 30 to break out the loop JE DISPLAY_MSG ;jumping to display to show JMP GO_TOP DISPLAY_MSG: MOV AH,9 LEA DX,MESG INT 21H ret MESG DB 0DH,0AH,"The Program Cannot Accept anymore characters$"