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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I’m new to learning assembly language, and I’m wondering what the command int 21h means. It is therefore entirely possible to use a far-call instruction to start the interrupt-function manually after pushing the flag register. 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 using this site, you agree to the Terms of Use and Privacy Policy. By calling it with different parameters in the registers mostly ah and al you could access various IO operations, string output and more.

For example, 21y 21H 808 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. 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.

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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.

Philip Kirkbride 7, 26 82 It comes under type 21h of various interrput tables, hence the lines of code goes like these as you mentioned. 21g in advance for your answer.

INT is an assembly language instruction for x86 processors that generates a software interrupt. This simply means that you are using function 01h of the Interrupt type Email Required, but never shown.

int 21h Dos Interrupt

It takes the interrupt number formatted as a byte value. Sign up using Facebook. 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. Sign up or log in Sign up using Google. 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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What does “int 21h” mean in Assembly? – Stack Overflow

Most Unix systems and derivatives do not use software interrupts, with the exception of interrupt 0x80, used to make system calls. Sign up using Email and Password. 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 From Wikipedia, the free encyclopedia. Post as a guest Name. By using our site, you acknowledge that you have in and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Other INT instructions are encoded using two bytes.

Retrieved from ” https: This page was last edited on 8 Octoberat One of the most useful DOS software interrupts was interrupt 0x Abraham Jacob 51 1 1. Instruction Set Reference Manual”. Post Your Answer Discard By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of ijtprivacy policy and cookie policyand that your 21n use of the website is subject to these policies.

INT X where X is the software interrupt that should be generated