ok, thanks.
it is ever the same : first i don't find anything and think this must be a new problem (because trisa=0 makes all i need)! and then when i know there is a mistake at me, i find the informations very quick... ;-)

adcon1 = 7 ' switch from analog to digital

nice description :
http://www.picbasic.co.uk/forum/showthread.php?t=561