INT 21H 8086 PDF

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)

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

Depending on the context, compileror assemblera software interrupt number is often given as a hexadecimal value, sometimes unt a prefix 0x or the suffix h.

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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.

assembly language int 21h Dos Interrupt

When generating a software interrupt, the 88086 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. It is therefore entirely possible to use a far-call instruction to start the interrupt-function manually after pushing the flag register.

One of the most useful DOS software interrupts was interrupt 0x By calling it with different parameters in the registers mostly ah and al you could access various IO operations, string output and more. Most Unix systems and derivatives do not use software interrupts, with the exception of interrupt 0x80, used to make system calls. This is accomplished by entering a bit value corresponding to a kernel function into the EAX register of the processor and then executing INT 21n The INT 3 instruction is defined for use by debuggers to temporarily replace an instruction in a 21u program in order to set a breakpoint.

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Other INT instructions are encoded using two bytes. Since the dedicated 0xCC opcode has some desired special properties for debugging, which are not shared by the normal two-byte imt for an INT 3, assemblers do not normally generate the generic 0xCD 0x03 opcode from mnemonics.

From Wikipedia, the free encyclopedia. INT X where X is the software interrupt that should be generated Instruction Set Reference Manual”.

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