is an eight-bit microprocessor
, the first sold by MOS Technology
. The 6501 is the first member of the 65xx series
of microprocessors. It was the first microprocessor to be sold for $25 in unit quantities. It was created by several ex-members of Motorola's design team and was pin-compatible with the Motorola 6800
microprocessor. It was not software-compatible, offering several addressing modes not available on the 6800.
The 6502 is a 6501 with the pins re-arranged following a lawsuit by Motorola over the 6501's pin arrangement. As a result of the lawsuit, MOS was forced to pay the legal costs and promise to destroy every 6501 they had manufactured. The 6502 also added a two-phase clock generator, so it only needed a single phase clock input, simplifying system design.