3 ms·
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 pa
by kstenerud 1y ago
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.
[1] https://en.wikipedia.org/wiki/Harvard_architecture https://en.wikipedia.org/wiki/Harvard_architecture
- ksherlock 1y agoThe 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
- userbinator 1y agoNo 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).