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Cycle-exact 6502 processor clone fits in 0.77% of a Spartan-7 (and Spartan-3) FPGA, powers VIC-20 PC

Xilinx Employee
Xilinx Employee
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In the 1970s, nearly every low-end microcomputer and video game from the Apple II to the Atari 2600 ran the opcodes of one immensely successful 8-bit microprocessor: MOS Technology’s 6502. Ted Fried at MicroCore Labs has created a cycle-accurate clone of the 6502 processor called the MCL65 and instantiated it in FPGAs. First up, Fried instantiated a version of the MCL65 in a $109 Digilent Arty S7 dev board containing a Spartan-7 S50 FPGA. The 6502 processor core consumes a mere 0.77% (that’s 0.0077) of the device so, presumably, if you really felt like it, you could stamp more than 100 of these processor cores into a low-cost FPGA, assuming you knew what you wanted to do with that many 8-bit processors.


Here’s a photo showing a most unlikely bridging of old and new technologies: a MicroCore MCL65 processor core instantiated in a Spartan-7 FPGA on an Arty S7 dev board plugged into the 40-pin MOS Technology processor DIP socket of a Commodore VIC-20 running Commodore Basic.



MicroCore Labs MCL6502 processor on an Arty S7 board running a Commodore VIC-20.jpg 


MicroCore MCL65 processor in a Spartan-7 FPGA on an Arty S7 dev board plugged into a Commodore VIC-20 running Commodore Basic




Commodore introduced the VIC-20 in 1980. That’s 37 years ago.


MicroCore Labs then instantiated the same core in a Spartan-3 S250E FPGA, using 490 LUTs and just 10% of the device.




MicroCore Labs MCL6502 processor on a Spartan3.jpg 



MicroCore MCL65 processor in a Spartan-3 FPGA plugged into a Commodore VIC-20

Old technology running even older technology






According to a recent LinkedIn post, Fried plans to release the core as open source. Contact him directly for more information.



For more stories and tall tales about the MOS Technology 6502 processor, see Tekla S Perry’s great article from IEEE Spectrum titled  “Atari Alumni Talk About the Tall Tales They Told to Launch an Industry,” which chronicles a meeting in 2016, sponsored by the IEEE Silicon Valley History Committee, that included Atari founders Nolan Bushnell, Al Acorn, and Owen Rubin with Chuck Peddle, who designed the 6502 at MOS Technology, chiming in from the audience.





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