That is what they seem to be labeled. I had always assumed that these "banks" were on 020+ but when I went back and reread the book it said 68000 and I didn't believe it until I looked up a Pin diagram of a 68000 and there were the pins. :eek:
I had figured that out. It seems they work differently from good old C64 banking out the ROM to get at the RAM underneath. But nevertheless my documentation says they are usable.
All I know is, the first 680x0 Asm book I ever bought (1985?) described this as separate usable banks of RAM that could be wired separately to literal different banks of RAM. But it says you can't use all 8 banks (don't know why, maybe because they were "reserved").
I reread it a few hours ago. Its all in there. It is of course possible that he did not word things quite right or that I am misunderstanding something....
But what is the purpose of the pins on 68000. u r saying they are like for an external MMU to write protect the CODE bank and that would be about it.
I say if the pins exist on an 060 then they can be wired up on the ram card as extra address lines. And the MMU could still do its thing. I don't see any reason why one must conflict with the other.
FC0-FC2 are used for systems that separate user data, user instruction, supervisor data and supervisor instruction into separate memory banks. In theory this expands your capacity and could prevent buffer overflow attacks somewhat like DEP on newer x86.
It's not user accessible though, it's fully controlled by the CPU involuntarily. When it fetches an instruction, those pins would bank select the user instruction bank, then when it fetches the data for that instruction, they toggle to the user data bank. In supervisor mode, it selects the supervisor banks instead.
These are just set by the CPU along with the address strobe, no user intervention is even possible, so the hardware and operating system have to be designed from the beginning to work this way or ignore them and have one big chunk of memory.
By the time the 060 was made it was pretty clear nobody was using them so they just went away.
