What is int21h?

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.

Which interrupt called DOS interrupt?

Interrupt vectors used by DOS

Interrupt vector Description Notes
20h Terminate program Implemented in DOS kernel
21h Main DOS API Implemented in DOS kernel
22h Program terminate address Return address in calling program
23h Control-C handler address Default handler is in the command shell (usually COMMAND.COM)

What is int 21h and INT 10H?

Use INT 10H function calls to: – Clear the screen. – Set the cursor position. – Write characters to the screen in text mode. Use INT 21H function calls to: – Input characters from the keyboard. – Output characters to the screen.

How are interrupts processed inside a MS-DOS system?

Interrupts may be generated by external devices (external hardware interrupts) or by the CPU (processor interrupts). Processor interrupts may be caused by processing errors (internal hardware interrupts) such as an attempt to divide by zero or by an INT instruction (software interrupt).

What is the function of INT 10h with AH 09h?

Interrupt number 10h (INT 10h)

INT 10h Service no. 09h Inputs any
AH=09h; write Character and attribute at cursor position input AL =Character to Display. BH =page number. BL =attribute. CX =number of times to write Character.

What is INT 21h and INT 10H?

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 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

How to create a loop using INT 21h?

I tried to create a loop which compares the current time to the initial time, using int 21h, function 2Ch with the hundredths value in DL, but it seems to be too slow… I would rather use BIOS int 1Ah, which is used as source for that int 21h service any way, and this may be a bit simpler to use.

What is the function code for int 17?

SeeAlso: INT 17/AH=00h AH = 06h – DIRECT CONSOLE OUTPUT Entry: DL = character (except FFh) Return: AL = character output Notes: does not check ^C/^Break SeeAlso: AH=02h,AH=09h AH = 06h – DIRECT CONSOLE INPUT Entry: AH = 06h DL = FFh Return: