[that_jojo]

I've been writing to 65816 lately, so it may be that they're extended mode instructions. But does the 6502 not have PHX and PHY?

[jroesner]

The 65C02 does (as well as AFAIK the 6510) if one compiles VASM with the according flags. Ben decided not to do so, neither did I for the feeling of good old times. Why make it easy ;)

[jimsmart]

The 6510 is what’s in the C64 - PHX and PHY definitely aren’t supported there (source: I was programmer on multiple published games, back in the day).

The NES is similar family too, and doesn’t have those opcodes - but the Atari Lynx has them (being 65C02).