What is the function on INT 21h?

What is the function on 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 is the function of 0Ah of INT 21h?

INT 21H functions

Function number Description
0Ah String input
4Ch e.g. mov ax,4C00h int 21h Terminate the current program (mov ah,4Ch int 21h is also used.)

What is the function of INT 21h in 8086?

3 Answers. 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…

What is the function of 4Ch of INT 21h?

INT 21h function 4Ch is preferred….INT 21h – The general function despatcher.

Action: Outputs a character to the standard output device. I/O can be re-directed, but prevents detection of ‘disc full’.
On entry: AH = 02h DL = 8 bit data (usually ASCII character)
Returns: Nothing

What is the meaning of int 03h instruction?

The INT3 instruction is a one-byte-instruction defined for use by debuggers to temporarily replace an instruction in a running program in order to set a code breakpoint. The more general INT XXh instructions are encoded using two bytes.

What are the DOS function calls?

To use a DOS function call in a DOS program, place the function number in AH and other data that might be necessary in other registers. The first byte of the buffer contains the size of the buffer (up to 255). The second byte is filled with the number of the characters typed upon return.

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.

What does INT do in assembly?

INT is an assembly language instruction for x86 processors that generates a software interrupt. It takes the interrupt number formatted as a byte value.

Why do we use 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 . In MS-DOS, invoking interrupt 21h while AH = 4Ch causes the current process to terminate and uses the value of register AL as the exit code of the process.

What does int stand for?


Acronym Definition
INT Internal
INT Interest
INT Introduction
INT Integer

Are there any non functional functions in INT 21h?

INT 21h in the 512’s implementation of DOS Plus 2.1 provides 77 official functions, two of which are non-functional and return with no action. Within this range some calls have subfunctions which further extend the range of operations. In all calls, on entry AH defines the function.

Which is better INT 21h or INT 4CH?

INT 21h function 4Ch is preferred. Reads a character from the standard input device and echoes it to the standard output device. If no character is ready it waits until one is available. I/O can be re-directed, but prevents detection of OEF.

How to call program terminate routine INT 21h?

In all cases the general programming technique is to set AH to the function pointer, set up the required register contents (and the memory block if necessary) then to issue the call by the assembly code INT instruction. To call the recommended program terminate routine, INT 21h function 4Ch, the relevant parts of the code would be:

Where are the register contents of INT 21h stored?

If spawning is employed register contents which must be be preserved should be pushed onto the stack, and the stack registers themselves (i.e. SS:SI) should be saved in known memory locations for explicit later retrieval. INT 21h functions 00h to 24h are based on and are, with a few exceptions, direct equivalents to the corresponding CP/M calls.

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