What is the function of 09h of INT 21h?

INT 21h – The general function despatcher

Action:	Writes a string to the display.
On entry:	AH = 09h DS:DX = segment:offset of string
Returns:	Nothing
Notes:	The string must be terminated by the $ character (24h), which is not transmitted. Any ASCII codes can be embedded within the string.

What does 09h mean in assembly language?

Instruction Statement The contents of the AH register are used to specify the function to be invoked. When INT 21h is involved, it directs program flow to that function, and then return to the program after the function is done. Example: DOS function 09h: display a string of characters whose offset is specified by DX.

What is function of MOV A 21h?

What is the function of MOV A 21H?

Function number	Description
01h e.g. mov ah,01h int 21h	Keyboard input with echo: This operation accepts a character from the keyboard buffer. If none is present, waits for keyboard entry. It returns the character in AL.

Which DOS INT 21h command is write a character to output?

2
INT 21h / AH=2 – write character to standard output. entry: DL = character to write, after execution AL = DL.

Why do we use INT 21h and 4CH at the end of every program?

We always have to put some number(number of the function) into ah register when we are using an interrupt. on ah=4ch int 21h , the program will terminate control to the operating system. (end the program) And int 21h is a dos interrupt.

What is int 21h in assembly language?

int 21h means, call the interrupt handler 0x21 which is the DOS Function dispatcher. the “mov ah,01h” is setting AH with 0x01, which is the Keyboard Input with Echo handler in the interrupt.

What does CMP do in assembly?

The CMP instruction compares two operands. It is generally used in conditional execution. This instruction basically subtracts one operand from the other for comparing whether the operands are equal or not.

What is the use of mov ah 4CH?

MOV AH, 4CH means store (or “move”) the hexadecimal value 4C into register AH . INT 21H means invoke the interrupt identified by the hexadecimal number 21 .

What is 0DH?

DB is one of two commonly used memory initialization assembler directives, the other being DW. Both ‘0AH’ and ‘0DH’ are bytes being stored/initialized in storage, while ‘0’ is NULL commonly used to terminate string literals.

How do you use INT 21h?

INT 21H will generate the software interrupt 0x21 (33 in decimal), causing the function pointed to by the 34th vector in the interrupt table to be executed, which is typically an MS-DOS API call. This simply means that you are using function 01h of the Interrupt type 21…

How do you use INT 10H?

To use this call, load AH with the number of the desired subfunction, load other required parameters in other registers, and make the call. INT 10h is fairly slow, so many programs bypass this BIOS routine and access the display hardware directly.

What does ” INT 21h ” mean in assembly language?

I’m new to learning assembly language, and I’m wondering what the command int 21h means. For example: Which should read a key from the user. int 21h means, call the interrupt handler 0x21 which is the DOS Function dispatcher. the “mov ah,01h” is setting AH with 0x01, which is the Keyboard Input with Echo handler in the interrupt.

What does ” MOV Ah, 01h ” mean in Assembly?

int 21h means, call the interrupt handler 0x21 which is the DOS Function dispatcher. the “mov ah,01h” is setting AH with 0x01, which is the Keyboard Input with Echo handler in the interrupt. See:

What are the function codes for DOS INT 21h?

SeeAlso: AH=02h,AH=09h AH = 06h – DIRECT CONSOLE INPUT Entry: AH = 06h DL = FFh Return: ZF setif no character available and AL = 00h

Is it bad to call DOS function 09h?

However, the approach is still far from ideal; calling DOS function 09h to print a string from within the interrupt handler seems pretty harmful. If the main thread would call DOS functions itself (not uncommon in a real-life application), the whole program could crash and burn due to DOS being not re-entrant.