6502 datapath control timing fix
This odd structure appears several times in the 6502 datapath.
In the picture below, there are yellow rectangles to show the North and South ends of the poly where the shape shows possible contact cut positions. At the North end a contact cut is visible, but not at the South ends.
That is, the gates were originally laid out so they could be clocked by not-phi1 but in fact are clocked by phi2. They control the X and the Y driving onto SB (special bus). There's another pair like them further along, which control the driving of the A onto the SB and the IDB. Seems like a fix for a timing marginality?
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