What is the function of 4ch of INT 21H?
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 |
| Notes: |
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 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 are the dos interrupts?
Interrupt vectors used by DOS
| Interrupt vector | Description | Version |
|---|---|---|
| 24h | Critical error handler address | 1.0+ |
| 25h | Absolute disk read | 1.0+ |
| 26h | Absolute disk write | 1.0+ |
| 27h | Terminate and stay resident | 1.0+ |
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 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 does mov ah 4CH mean?
MOV AH, 4CH means store (or “move”) the hexadecimal value 4C into register AH . 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 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 are DOS and BIOS interrupts?
DOS and BIOS interrupts are used to perform some very useful functions, such as displaying data to the monitor, reading data from keyboard, etc. They are used by identifying the interrupt option type, which is the value stored in register AH and providing, whatever extra information that the specific option requires.
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 Dosseg?
DOSSEG is what is called an assembler directive. It is not assembly language, but a code telling the assembler to perform a certain task. In this case, it tells the assembler to use paragraph alignment for all segments.
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.
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 is the sub function of the INT 44h?
Function 44H (0x44 or 68), Sub function 0DH (0x0D or 13) I/O Ctrl –> generic I/O control for block devices This sub function provides a general-purpose mechanism for communication between application programs and block-device drivers.
What does INT 21h mean in MS-DOS?
INT 21H means invoke the interrupt identified by the hexadecimal number 21. Apparently some operating system (most probably MS-DOS, or more likely nowadays something emulating MS-DOS,) catches invocations to interrupt 21h and performs some operating-system-dependent function which is identified by the value of register AH.