How similar were the MC6800 and MOS 6502?

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When reading about the history of the 6502 CPU, it is regularly pointed out that Chuck Peddle had previously worked on the MC6800 CPU at Motorola. As well, it is stated that the goal when creating the chip was to produce a cheaper alternative to the 6800, and that was achieved when you compare that the 6800 cost $300 versus the 6502's $20 introductory price. On further reading, there are also mentions of the rare 6501 chip which was actually pin compatible with the 6800 and thus presumably could be a drop-in replacement, though not binary compatible.

So the question is how similar were the two competing microprocessors? Was the performance the same? How [dis]similar were the instruction sets? As well, could a 6501 be dropped into a 6800 socket and work with an existing motherboard despite not being binary compatible?

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