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The 8th bit was never ignored, it was for phase, and for example determined if you saw green or orange. Probably the best ref for this is from '83, Gayler's "The Apple II Circuit Description."

edit: corrected below, rev 0 non RFI (without the aux vid pin) ignored DL7



Actually, the very first Apple IIs only supported 4 colors in hi-res mode. The 8th bit was ignored.

A later revision added support for 6 colors, using the 8th bit to shift the pixels and change the pallet.


Thank, I just consulted appendix B of my copy, you are correct. DL7 is unconnected in nonRFI rev0 though every later Apple II RFI or not could do 6 color HIRES.




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