Author Topic: Missing opcodes ?  (Read 920 times)

Offline ldelabre

  • New Member
  • Posts: 1
Missing opcodes ?
« on: May 23, 2020, 10:07:53 AM »
Hi,
I'm working on a 8086 emulator (for fun) and I'm using NASM to generate my test-cases.
According to the Intel manual of 1978, the ADD instruction exists as opcode 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x80, 0x81 as well as 0x82 and 0x83 (kinda redudant with 0x80 & 0x81 but anyway).

So good for my test cases :p

What's more of a concern, is that the disassembler seems also to not recognize those opcode : 0x82, 0xc0, 0x00 (add al, 0) is view as a DB sequence whereas Visual Studio disassembly get it right:
0000001B  82                db 0x82
0000001C  C0                db 0xc0
0000001D  00                db 0x00

Is this on purpose ?

Sincerely,
Ludovic.

Ps : https://software.intel.com/en-us/forums/watercooler-catchall/topic/309628