josephoswaldgg@hotmail.com wrote:
I'm not clear on what version of the II you are trying to implement. It might be best to go for (at least start with) one of the II/II+ models, with 48k RAM because all the logic was synthesized with pure TTL, and you can get schematics from various sources (someone has the old 1978 "Redbook" reference manual scanned into a PDF).
I started with the ][ but quickly moved on to the ][+. I can see that the IIe was more complicated so I'm sticknig with the earlier models first. And yes, I found the redbook pdf, but reading the schematics doesn't readily reveal what parts *must* be there for the ROMs to run BASIC properly, for example.
The softswitch behavior got more complicated with later models as well. DOS 3.3 games like Lode Runner usually can run in a 48K original II just fine.
I 'crippled' MESS last night to a point where only the keyboard function for C00X & C01X were included, plus the sceen mode switches at C05X. Everything else was gone and Applesoft BASIC still ran fine. So it seems I have a problem with my design, rather than not having something critical implemented.
I don't have a reference manual handy, but I believe the INTCxROM softswitch is used to control whether $c100..$cfff was mapped ROMS on expansion slots or the expanded ROM space in a IIe that contained, as I recall, diagnostic routines, 80 column firmware support, and maybe some other miscellaneous code. Yet another way, along with its built-in language card & 64k expansion support, readable soft-switches, VBLANK connections, etc., that a IIe is more complicated than a II/II+. About the only thing simpler in a IIe is the lack of memory config jumpers.
OK, thanks, that's useful to know! Thanks again for taking the time to reply! Regards, -- | Mark McDougall | "Electrical Engineers do it | <http://to be announced> | with less resistance!"