The MCL65 is an open source, cycle accurate, microsequencer-based FPGA core which can be used as as an embedded processor or as a drop-in replacement for the MOS 6502.

The core uses a 16-bit microsequencer which allows it to be cycle acurate and structurally compatible with the MOS 6502 microprocessor. Both the bus interface and the ALU are implemented in microcode which results in an extrememly small core that leaves the majority of the silicon available for other logic.

It has successfully been used in a Commodore VIC-20, Apple II+, Apple IIe, and Atari 2600.