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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This is accomplished by entering a bit value corresponding to a kernel function into the EAX register of the processor and 80886 executing INT 0x 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.

Geoffrey 6, 2 17 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.

This page was last edited on 8 Octoberat Views Read Edit View history. It comes under type 21h of various interrput tables, hence the lines of code goes like these as you mentioned.

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Instruction Set Reference Manual”. Thanks in advance for your answer. Most Unix systems and derivatives do not use software interrupts, with the exception of interrupt 0x80, used to make system calls.

assembly language int 21h Dos Interrupt

I’m new to learning assembly language, and I’m wondering what the command int 21h means. Other INT instructions are encoded using two bytes. This simply means that you are using function 01h of the Interrupt type Post Your Answer Discard 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.

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For example, INT 21H will generate the software interrupt 0x21 33 in decimalcausing the function pointed to ibt the 34th vector in the interrupt table to be executed, which is typically a DOS API call. From Wikipedia, the free encyclopedia. By using this site, you agree to the Terms of Use and Privacy Policy.

Post as a guest Name. By using our site, you acknowledge that you have read and understand our Cookie Policy 8068, Privacy Policyand our Terms of Service. INT is an assembly language instruction for x86 processors that generates a software interrupt. Retrieved from ” https: Sign up using Email and Password.

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What does “int 21h” mean in Assembly? – Stack Overflow

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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.

BOSS 8 23 INT X where X is the software interrupt that should be generated 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.

It takes the interrupt number formatted as a byte 21u. It is therefore entirely possible to use a far-call instruction to start the interrupt-function manually after pushing the flag register.

int 21h Dos Interrupt

Sign up using Facebook. Sign up or log in Sign up using Google. When generating a software interrupt, the processor calls one of the 0886 pointed to by the interrupt address table, which is located in the first bytes of memory while in real mode See Interrupt vector.