Thanks Jpanhalt, i read your kind offering....it seems like if a PIC has LAT registers then RMW problems are less likely but still not avoided completely.
I must admit i am grateful Jpanhalt, because your article there is the first time i have had any inkling of understanding of what RMW is....its about the changing voltages in there , and it being read before the voltage had chance to change.
I am now thinking we need to use some sort of emulator and step through our code....the non working ones just dim to 75% and wont respond to DALI dimming commands.