650X Schematic Notes

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Notes on the original 650X schematics from MOS Technology.



Donald F. Hanson, Ph.D., had written a 1995 paper based in part on the 6502 blueprints. His original work was to reverse engineer a detailed block diagram of the processor. At the time he received the blueprints from MOS Technology in 1979, he had agreed to keep them confidential, except for educational use. Earlier this year (2011), visual6502.org contacted Dr. Hanson. After some negotiations, he agreed to provide scans of the original blueprints, for educational use only. The blueprints he received were labeled Rev. C and contained a preliminary design. Since the complete and error-free design (which we refer to as Rev D) is already known through the work of visual6502.org, Dr. Hanson felt that he could provide the Rev. C blueprints to visual6502.org for their historical value, provided that they be used for educational use.

ID from sheet 1 "bottom half" (bears the date 11-74)
ID from sheet 2 (bears the date 8-12-75)


Description and images of the two sheets, which will contain side text 'Courtesy...'

Mention the dates on the ID labels, the very close correspondence to chip layout.

Pin Names

Mention at least SYNC and SO pin names, also the names on unbonded pins.

Image of SO/C.P.S pin, and link to an account of 'Chuck Peddle Special'

Chip Versions: 6501 and 6502

Describe and illustrate the X/O boxes (around top edge of diagram)

Mention the 6501/6502 differences including the SYNC pin.

Also mention the 6504 (?)

Chip Revision C, ROR Bug, Other Errors

Mention and illustrate the missing/extra transistors in the PLA which give rise to the ROR bug

Also mention the other discrepancies in the PLA

Any other Rev C versus Rev D observations

Schematic Errors


Logic gates and Transistors

Mention and illustrate the presence of gates and transistors, the transistor sizes and die sizes in mils (thousandths of inch) and the presence of internal signal names - use the cross-coupled D1x1 latch to illustrate. Compare with Balazs' schematic.


Thanks to the following for their observations and assistance

  • Edgar F
  • Segher Boessenkool
  • Michael Steil
  • Donald F Hanson, for making the scans of the 6502 available to us, and
    • Department of Electrical Engineering, University of Mississippi, University, MS, for supporting Prof. Hanson’s work on the 6502 including the drafting of the block diagram.


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