MS-DOS uses INT 21H for its main API functions which provide a low-level is the assembly code to transfer data from one file to other using INT 21H?. INT is an assembly language instruction for x86 processors that generates a software interrupt. For example, INT 21H will generate the software interrupt 0x21 (33 in decimal), causing the function pointed to by the 34th vector in the interrupt. int 21h Dos Interrupt. Int 21h is a common function. The INT 21H instruction in is a software interrupt to vector 21H. It is used for input/output operations.
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INT (x86 instruction)
It is therefore entirely possible to use a far-call instruction to start the interrupt-function manually after pushing the flag register. It takes the interrupt number formatted as a byte value. This is accomplished by entering a bit value corresponding to a kernel function into the EAX register of the processor and then executing INT 0x Other INT instructions are encoded using two bytes. Thanks in advance for your answer.
assembly language int 21h Dos Interrupt
For example, INT 21H will generate the software interrupt 0x21 33 in decimalcausing the function pointed to by the 34th vector in the interrupt table to be executed, which is typically a DOS API call. This page was last edited on 8 Octoberat Sign up using Facebook. Most Unix systems and derivatives do not use software interrupts, with the exception of interrupt 0x80, used to make system calls.
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Retrieved from ” https: When generating a software interrupt, the processor calls one of the functions pointed to by the interrupt address table, which is located in the first bytes of memory while in real mode See Interrupt vector.
By calling intt with different parameters in the registers mostly ah and al you could access various IO operations, string output and more. Philip Kirkbride 7, 26 82 Sign up or log in Sign up using Google. One of the most useful DOS software interrupts was interrupt 0x Since the 21y 0xCC opcode has some desired special properties for debugging, which are not shared by the normal two-byte opcode for an INT 3, assemblers do not normally generate the generic 0xCD 0x03 opcode from mnemonics.
Abraham Jacob 51 1 1.
Depending on the context, compileror assemblera software interrupt number is often given as a hexadecimal value, sometimes with a prefix 0x or the suffix h.