The 68k was unique in that it included in its design the ability to act as a Harvard Architecture processor (where instructions and data have separate signal pathways rather than being together in the same address space [1])
It did this via the function code pins, which signaled differently depending on whether the chip was requesting instructions or data, in supervisor or user mode. No other consumer-grade chip had this as far as I know.
Sega's System 16 was also 68000 based (as was the Megadrive/Genesis), but I don't know anything about their protection scheme.
The 65816 has valid data address (vda) and valid program address (vpa) pins which are essentially the same as fc0/1/2 , minus the supervisor/user mode support.
vda vpa
0 0 internal operation, address bus may be invalid
0 1 valid program address, may be used for program cache control
1 0 valid data address, may be used for data cache control
1 1 opcode fetch, may be for program cache control and single step control
No other consumer-grade chip had this as far as I know.
The 8086/88 has status outputs which provide similar information, including which segment register is being used (CS, DS, ES, SS) and the type of bus cycle (interrupt acknowledge, read I/O, write I/O, halt, opcode fetch, read data, write data).
IIRC Sega’s System 16 did something similar. Was that board’s encryption cracked in the same way?
Was this style of anti-piracy measure widely used at the time, or was it only on a few 68000-based systems?