INT 21H 8086 PDF

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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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. By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.

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 Geoffrey 6, 2 17 This simply means that you are using function 01h of the Interrupt type By calling it with different parameters in the registers mostly ah and al you could access various IO operations, string output and more.

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assembly language int 21h Dos Interrupt

Since the dedicated 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. INT X where X is the software interrupt that should be generated Stack Overflow works best with JavaScript enabled. One of the most useful DOS software interrupts was interrupt 0x Views Read Edit View history. This page was last edited on 8 Octoberat 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.

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

It comes under type 21h of various interrput tables, hence the lines of code goes like these as you mentioned. By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy 21gand our Terms of Service. I’m new to learning assembly language, and I’m wondering what the command int 21h means.

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INT (x86 instruction) – Wikipedia

Philip Kirkbride 7, 26 82 Post as a guest Name. BOSS 8 23 Other INT instructions are encoded using two bytes. INT is an assembly language instruction for x86 processors that generates a software interrupt. 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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INT (x86 instruction)

Instruction Set Reference Manual”. Retrieved from ” https: It takes the interrupt number formatted as a byte value.

Email Required, but never shown. From Wikipedia, the free encyclopedia. The INT 3 instruction is defined for use by debuggers to temporarily replace an instruction in a running program in order to set a breakpoint. 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, 21n is typically a DOS API call.