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?
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.
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 controlThe 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).