Re: How much?
Most of the pins stayed the same (all the data lines, address lines, power, and I think interrupts are in the same place on the 6800 and 6502) - what changed were the area around the clock (the 6800 required a two phase non-overlapping clock, the 6502 was driven from a single clock signal and generated ) and bus controls (e.g. the 6800 has a tristate control, valid memory address signal and data bus enable that are lacking on the 6502). Unless you were using a DMA controller that needed to take over the bus, the changes probably made the 6502 a little easier to design for than the 6800.
The 6501 bus interface was closer to the 6800 version - and too close for Motorola's liking.
Biting the hand that feeds IT
