I was working on an infocus projector unit that used coldfire microprocessors. but ill save that for another day another topic another forum. hehe.
As far as the idea i had, i was going to use the internal flash of the ATmega to hold the ROM images instead of an external chip, that way i can use less chips as possible. probably use a simple mainloop subroutine that looks at the address, does some simple address math and fetches the databyte on a read call. then the ports are switched on and outputted on the ports during an OE=true request. and anytime the OE is false, i tri-state the port outputs of the AVR into a high-Z state, probably not necessary but ill do it anyway. if i ran the atmega at 18 or 20mhz, it wouldnt really be a bottleneck for address/data fetches as the macintosh is running a mere 8mhz.
As far as the idea i had, i was going to use the internal flash of the ATmega to hold the ROM images instead of an external chip, that way i can use less chips as possible. probably use a simple mainloop subroutine that looks at the address, does some simple address math and fetches the databyte on a read call. then the ports are switched on and outputted on the ports during an OE=true request. and anytime the OE is false, i tri-state the port outputs of the AVR into a high-Z state, probably not necessary but ill do it anyway. if i ran the atmega at 18 or 20mhz, it wouldnt really be a bottleneck for address/data fetches as the macintosh is running a mere 8mhz.