byuu mentioned that 512 mode double-pumps the DAC - I assume that means the pixel clock goes faster for those lines so you have twice as many pixels per master cycle.
ETA: Alternatively the pixel clock is always fast enough for 512 but they normally feed each pixel twice. Either way we know it doesn't impact the actual H or Vsync timing or else the screen wouldn't sync when you did a split like that.
Last edited by R. Belmont; 08/17/09 08:15 PM.