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65816 to Z80 switch - how to?

I experimented with MultiCPU utility.
It's based on IRQ exchanging CPUs and its modes:
8502 @2MHz
8502 @1MHz
Z80
65816 native mode @20MHz

All is working correctly if I have disabled SCPU (65816) - then is change between 8502 1/2MHz and Z80 ok, of course switch to 65816 is not available so this is skipped.
When I enable SCPU (65816) then it works at all except switch to Z80 - so 8502 1/2MHz uses 65816 emulated mode @1MHz and switch 1/2 MHz is done by 8502 clocking, then switch to 65816 native mode @20MHz is working too. But when I want to switch to Z80, it works not and real switch is skipped (better wrong written) when is leaving control to Z80 and then is used RTS to continue in IRQ after Z80 code execution.

So, I know and everybody too how to switch 8502 to Z80 - BUT HOW TO DO THE SAME WITH 65816 emulated mode to Z80?
65816 emulated mode = same as 65xx/8502 except Emulation status and opcode XCE
65816 native mode = full power of 16-bit CPU
Thank you for every help!
 
Miro

Any interest in doing more

Any interest in doing more modern processors?  I would imagine that ARM's run a magnitude faster.  
We looked at the 816 way back when and we got stuck on things like very limited register arrays, an X and Y was 14 or 30 less than the other 16bit.
 
Bil

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