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Whats the HEX value for each opcode? (example: "$A1" = "MOV EAX")

Posted on 2004-09-02
Medium Priority
Last Modified: 2009-12-16
Is there any place where I can see the hex value for each or almost all Opcodes?

For example:

$A1  =  MOV EAX

Please, I need it kinda fast....
Thank you!!!
Question by:teste123
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Expert Comment

ID: 11966997
It has much to do with which processor the opcodes are for...

You could go to www.microchip.com for example, and grab the data and programming sheets for a particular device and you'll be a few steps closer.

The instruction set summary usually shows the mneumonic and the actual bit structure.

Author Comment

ID: 11967024
What I wanted I've found here:


Expert Comment

ID: 11986306
Intel's official processor guides give you nice opcode maps, too.
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Author Comment

ID: 11988672
What I really want now is something that shows me the size of each Opcode... Do you have any?
If you do, I'll increase to 450 and accept it.

Accepted Solution

aib_42 earned 600 total points
ID: 11993342
Check out the 2nd part of the 2nd volume of the Pentium 4 Software Developer's Manual:
http://www.intel.com/design/pentium4/manuals/index_new.htm#sdm_vol2b (P4 Manuals index)
ftp://download.intel.com/design/Pentium4/manuals/25366714.pdf (Direct link)

The Appendices A and B would give you all the information you would need.

Assisted Solution

adg080898 earned 600 total points
ID: 12013380
The size of opcodes can vary depending on prefixes. Intel 32-bit processors really have three operand sizes for data, and two operand sizes for addresses.

For example, if this code runs in 16-bit mode:

mov eax,0x01234567

It will have an "opsize" prefix. This tells the cpu to expect a 32-bit operand. The opposite is true in 32-bit mode:

mov ax,0x1234

...is encoded with a prefix.

The address size can also affect the size of the opcode. If this runs in 16 bit mode:

mov ax,[eax]

...it will have an addrsize prefix.  The opposite is true in 32-bit mode:

mov ax,[bp]

...will have an addrsize prefix.

16-bit addressing modes are [bx], [si], [di], [bp], [bx+si], [bx+di], [bp+si], [bp+di], or any of those with a constant offset.

32-bit addressing modes are [reg], [reg+reg], [reg+reg*2], [reg+reg*4], [reg+reg*8], or any of those with a constant offset (example: [eax+ebx+128])

The x86 instruction format is quite complex.

Expert Comment

ID: 12035124
just type in the codes you want, assemble the program and go look at it with turbo debugger. on the left side of each instruction it has the exact opcode that the proccessor runs.
like mov ax,1 would look something like  0B80100 or something like that.

Expert Comment

ID: 12035490
See http://www.sandpile.org/ia32/index.htm

It has charts for opcodes.

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