The loop and wait idea is just not exact enough to keep the screen from jittering. As I said, it works with the HS setting, but is not quite fast enough.If the PLL really stops and starts accurately enough, it should give me the speed to update the pixel registers without losing a horizontal line. Right now, the characters have a one line space between each pixel. It's still very legible, but I'd like the letters in solid blocks. The character generator runs in machine language,currently on a '819. The update is performed by a seperate PIC using PBP with a shiftout subroutine.