#6809
Are you aware that the Hitachi 6309 (CMOS 3 Mhz 6809) has a bunch of
un-documented new and nifty features? Things like trapping illegal
opcodes, more 16-bit registers, and a few more cool things that I
can't remember at the moment. We tried them and they seem to work.
The story we got is that Hitachi implemented the features and
documented them in Japan but never released any info in the states
due to some issue with Motorola.