> A related issue: are the 16C62x parts plug-compatible with 16c61? I
> understand they have extra comparators, but if I just program a 16c620
> with object built for the 16C61, will it work the same?

The 16C62x and 16C61 have slightly different memory maps; in addition, you
must explicitly enable PORTA digital inputs if you intend to use them for
anything.  Converting your source file to be 16C62x compatible should be
very easy, but loading object code directly will not work.