65816 instruction set


Warning! Strictly "IMHO" kind of reply without any flame war intended: Sorry, but I often see the opposite. Ie C64 coders wants SuperCPU (equipped with 65816) just for a "faster 6502" (minus the illegal opcodes though), and not so much using the other inventions of 65816, only the speed. And especially because C64 and C65 were 8 bit designs, I can't see why to move to 65816, where no Commodore machine was released with that CPU for real. Yes, it would be NES whatever, not so much a CBM-like machine then (so then it can be a Mega-NES project, but not a C65-Mega65 project). It's an interesting question, since if you feel that "easy programming" is the main factor, you can even find some more modern 32 bit CPU to do then, with FPU built-in, linear addressing of Gbytes of memory, multiple CPU codes, whatever. But I'm sorry, nothing offensive attitude from me here, just I can't see your point. Mega65 after all is an "greatly enhanced" C65, by definition, what do you expect exactly then? But to be fair, Mega65 has already great capabilities to break the barriers of a typical 65xx 8 bit design, like the ability to address the whole memory space with a specialized addressing mode. Also, already the 4510 in the C65 had some 16 bit math support, can be kind of useful (like INW, DEW opcodes). I could even demonstrated, that on Mega65 it's possible to software emulate an intel 8080 CPU kinda well, and running CP/M applications, which exploits the features discussed above (without this it would be ten fold slower, or even more ...). And maybe more comes with helps even math integer unit, etc. And who knows, as far as I know, since it's planned to have multiple "CPU personalities" maybe 65816 opcodes can be accessed anyway for a software requesting it. But since the major point of Mega65 (starting with the case design already!!!) is being a "mega"-"C65", and C65 is a kinda well defined machine, just replacing everything without a totally different specification would undermine the whole project, by its very roots and basic goals.


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