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Editorial Team
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Asked: 2026-06-05T09:29:57+00:00

I’m writing a piece of assembly code designed to get keyboard input using a

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I’m writing a piece of assembly code designed to get keyboard input using a BIOS interrupt, then print it to the screen with another BIOS interrupt. I am using the NASM compiler for x86 systems. At line 19 of my code (marked with an asterisk (*), I am getting the “invalid combination of opcodes and operands” error. I know this generally represents any number of syntactical errors, but at my skill level, I can’t work down to any specifics, sorry. Here’s my code chunk:


; ---------------------------------------------
; Get input (hangs on input and loops forever)
; ---------------------------------------------
GetInput:



XOR AH, AH                 ;AH = 0 for interrupt 16.0
INT 0x16                   ;Fetch the next key pressed.
MOV SI, keymap             ;Set SI to the head pointer of the keymap
ADD SI, AH                 ;Increase the pointer by the key number.
*MOV AL, [SI]              ;Load the returned key for printing.
CALL PrintCharacter        ;Print the key
CALL GetInput              ;Wait on the next key.
RET

Let me know if you need any more information, thanks!

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1 Answer

  1. Editorial Team

    I believe that that your mistake is one line before.
    You can’t mix 16 bit and 8 bit registers in x86 like:

    ADD SI, AH

    If you want to add AH register to SI than copy (zero extend) AH to AX first, like:

    MOVZX AX, AH
ADD   SI, AX
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