Incompatibilities between the 64 mode & a real C64

[Blacklord]

These are what I know of, are there others ?

- Programs that write to $D030, used for clock frequency & a test bit for the VIC on the 128, but unused on a real C64
- $D02F is used for the extra keyboard matrix on the 128, this one shouldn't cause any problems when written to in C64 mode
- SID mirror registers don't exist on the C128
- Bit 6 at $01 on the 128 is used to tell whether the CAPS LOCK/ASCII DIN/ASCII CC key is pressed or not. On a poorly written C64 program this will cause it to crash if the location isn't masked properly
 - /EXROM on some cartridges causes problems

Any others ?

[Andrew Wiskow]

I'm not sure if this fits... but the "sparkling background" on some C64 programs when run in 64 mode on a C128 comes to mind...  I'm not sure what the technical term for this phenomonon is...

-Andrew

[einaroh]

I have no idea why, but the game Hawkeye never ran on my C128 in 64 mode.