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)

Philip Kirkbride 7, 26 82 This is accomplished by 21y a bit value corresponding to a kernel function into the EAX register of the processor and then executing INT 0x One of the most useful DOS software interrupts was interrupt 0x Abraham Jacob 51 1 1. INT X where X is 8068 software interrupt that should be generated Instruction Set Reference Manual”.

I’m new to learning assembly language, and I’m wondering what the command int 21h means. Stack Overflow works best with JavaScript enabled. Sign up using Facebook.

int 21h Dos Interrupt

Sign up using Email and Password. It comes under type 21h of various interrput tables, hence the lines of code goes like these as you mentioned.

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

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

This simply means that you are using function 01h of the Interrupt type 80886 Geoffrey 6, 2 17 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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This page was last edited on 8 Octoberat When generating a software interrupt, the processor calls one of the unt pointed to by the interrupt address table, which is located in the first bytes of memory while in real mode See Interrupt vector. From Wikipedia, the free encyclopedia.

assembly language int 21h Dos Interrupt

By calling it with different parameters in the registers mostly ah and al you could access various IO operations, string output and more. Views Read Edit View history. INT is an assembly language instruction for x86 processors that generates a software interrupt. It is therefore entirely possible to use a far-call instruction to start the interrupt-function manually after pushing the flag register.

BOSS 8 23 Since the dedicated 0xCC opcode has some desired special properties for debugging, which are not shared by the normal two-byte opcode for 80086 INT 3, assemblers do not normally generate the generic 0xCD 0x03 opcode from mnemonics.

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Thanks in advance for your answer. 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.

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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. 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. By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Other INT instructions are encoded using two inh. Email Required, but never shown.