816 in C64? too tricky for now!

Ed re-discovered his C64 (or, the box which claims to contain it) so we had a bit of a think about putting a 65816 in as a replacement for the 6510.

First off, the Level1B doesn't simply take all 40 pins of the host CPU socket into the CPLD, so it turns out we'd need an adapter simply because the power supplies are on different pins. Then we noticed that we connect the address bus directly to the 65816 - this has been OK for the Beeb, because it contains a transceiver and won't react to the address bus (running at 8MHz) unless the CPU needs a host access. And for a host access, we slow down to host speed.In a C64, the address bus is more of an actively shared resource, and we'd have to stay off the bus when we're not supposed to be using it. We'd need to react to AEC, so we need a 16-bit transceiver as well.

Finally, the 6510 has 6 i/o ports - we'd need to connect them to our general purpose I/O expander.

All in all, our Level1B would need a non-trivial adapter board to substitute for the 6510 in a C64. Probably this sub-project will have to wait for a Level2 board, or for some FPGA experiments, or maybe we'll attack the cartridge port instead.So Ed won't have to open that box after all.