In one of my first companies, InformAsic, we developed and shipped a small ASIC that implemented encryption for serial communication. The control was handled by AT-commands. And the parser and rest of the control functions was actually implemented in SW on the 6502 core in the chip. We clocked the chip at 33 MHz, making it one of the fastest 6502 clones in the early 2000s.
Nope. Most modems used in the '90s using the Rockwell chipset used a 6502 derived controller which was clocked at over 60 MHz. The NDA we had to sign to get access to the source code (to just modify some strings) was from another world and that's probably why it is not a very known fact.
