The pull-up resistors keep the state high until you pull it down with the action of the switch, otherwise the port is floating and un predictable results may occur.   

I am new to this ListServ, and out of the microcontroller world for about 8 yr's. I just read some stuff on the STAMP and find it a lot easier to deal with than the Motorola chips I use to work with.  

   Joe

-----Original Message-----
From:   TORRENS SR [SMTP:r139a@SMSERVER2.ULST.AC.UK]
Sent:   Monday, March 16, 1998 5:14 PM
To:     PICLIST@MITVMA.MIT.EDU
Subject:        buttens

cheers.

P.s what are the pull up resisters all about, should I be using them
?