6502.org

It's possible to test some of the undocumented instruction in Visual 6502.

Here's an example showing that document 2 is correct wrt the behaviour of AAX:

http://visual6502.org/JSSim/expert.html ... 0&steps=40

Thanks John, great link! That document is new to me.

I note that visual6502 is linked within, and is generally quite good for answering low level questions (as hoglet has just noted!), but unfortunately the visual6502 wiki is presently offline: please see the cached pages at archive.org for now.

Some time ago, Drass made a short list of the "illegal" NMOS 6502 instructions.

Couldn't find a post about it yet and just in case you don't already know: No More Secrets reached V0.99 last christmas (no Wham pun intended)
https://csdb.dk/release/?id=248511

Don't forget the classic pagetable.com article:

https://www.pagetable.com/?p=39

groepaz released his updated documentation No More Secrets V1.0 today: https://csdb.dk/release/?id=258111