Posted By
gerliczer
on 2009-02-08
08:54:42
|  Re: Need help with telephone program
Zero checking 53280 ($D020) is not a reliable way to determine if the program runs on a C64 or Plus/4. Large programs or BASIC programs that use a lot of variables may overwrite that RAM area in a Plus/4. Without initializing (reset) it should be considered to be in indetermined state.
It would be better to check something like reset vector ($FFFC/&FFFD) or IRQ vector ($FFFE/$FFFF) or KERNAL jump table (from $FF81) or KERNAL vector table data or BASIC vectors around $300 or maybe the processor port data direction register ($00).
Actually, even these methods could be seen as unreliable because they don't consider possible system expansions.
|
