Emulating unofficial opcodes

Discuss emulation of the Nintendo Entertainment System and Famicom.

Moderator: Moderators

Post Reply
User avatar
Posts: 642
Joined: Sun Mar 19, 2006 3:06 am
Location: Gothenburg/Sweden

Emulating unofficial opcodes

Post by oRBIT2002 » Wed Apr 07, 2021 12:38 pm

Some of these are doing two things at once. RLA rotates memory and AND's result with accumulator.
I'm trying to emulate this behaviour in my emulator but it's a bit confusing how to handle the CPU status flags. I have to emulate these behaviour with two 68k instructions (I'm on an Amiga atm), but how do I know which flags to use (the ones created from the memory shift or the and-operation)?
Hope you understand my problem.

EDIT: Here was the answer, well documented behaviour: https://www.pagetable.com/c64ref/6502/?tab=2#RLA

Post Reply