Here's another 65816 gotcha. The mx flags are set to the opposite of what I'd expect when using XCE to switch into native mode.

My best guess is that the designers wanted to save a little silicon, so they have the XCE instruction blindly swap E and C without much awareness of what the values actually are, and not try to be convenient by clearing mx. (Surely it's not that it's actually more common to be processing 8-bit data than 16-bit data on a 16-bit processor.)

And since m and x have to be set in emulation mode, they just happen to stay that way when switching to native mode.

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

IMO, having x and m initially set =1 when switching to Native Mode makes things a little more friendly for 6502 folks who want to experiment with the '816.

When they first enter Native Mode, they'll find it's actually very much like Emulation Mode (ie, much like 6502). Then later, after they've gotten used to Native Mode with m and x =1 they can experiment with m=0 and/or x=0.

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html