flat assembler
Message board for the users of flat assembler.

Index > Main > x86 opcode question

Author
Thread Post new topic Reply to topic
back`



Joined: 18 Oct 2007
Posts: 2
back`
does anyone understand the hex representation of x86 the opcodes
http://courses.ece.uiuc.edu/ece390/resources/opcodes.html

eg.
Code:
MOV   Reg,Imm    1011wrrr  8086   Move Data
    

so what does the wrrr mean?
Post 18 Oct 2007, 11:26
View user's profile Send private message Reply with quote
HyperVista



Joined: 18 Apr 2005
Posts: 691
Location: Virginia, USA
HyperVista
hi back' - this appears to me to be from an instructioni manual where they are trying to explain moving an immediate value (imm) (integer, etc.) to a register (reg). mov reg,imm as in mov ax,0x5.

regarding the 1011wrrr, look at the guide at the top of the spreadsheet on your link for an expaination of the meaning of rrr, mmm, sss, etc. it expains the opcodes for the various x86 instructions like mov, ret, etc.
Post 18 Oct 2007, 11:42
View user's profile Send private message Visit poster's website Reply with quote
MazeGen



Joined: 06 Oct 2003
Posts: 975
Location: Czechoslovakia
MazeGen
Bit w means operand size. w=0: 8-bit, w=1: 16/32-bit
Bit field rrr means 3-bit register code, from 0 through 7.

Example:

Code:
1011 0 000 MOV AL, imm
1011 1 111 MOV eDI, imm
    
Post 18 Oct 2007, 12:32
View user's profile Send private message Visit poster's website Reply with quote
bitRAKE



Joined: 21 Jul 2003
Posts: 2915
Location: [RSP+8*5]
bitRAKE
Attached is program by Svin that lets you play with encoding and see direct translation in mnemonic. It removes all confusion on the matter.

Please, look at the bottom of this page for other such useful tools by Svin.


Description: Small reference tool by Svin on instruction encoding.
Download
Filename: movrimm.rar
Filesize: 3.97 KB
Downloaded: 135 Time(s)

Post 18 Oct 2007, 23:58
View user's profile Send private message Visit poster's website Reply with quote
MazeGen



Joined: 06 Oct 2003
Posts: 975
Location: Czechoslovakia
MazeGen
[OFFTOPIC]
Hello bitRAKE! You're still around here? Good to see you again. I doubted you gave up assembly since long time ago. I still remember your great posts at asmcommunity Smile
[/OFFTOPIC]
Post 19 Oct 2007, 06:56
View user's profile Send private message Visit poster's website Reply with quote
Display posts from previous:
Post new topic Reply to topic

Jump to:  


< Last Thread | Next Thread >
Forum Rules:
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


Copyright © 1999-2020, Tomasz Grysztar. Also on YouTube, Twitter.

Website powered by rwasa.