Quote Originally Posted by biggej View Post
DT is on the right track but maybe for not exactly the right reason. The DS18S20 does not have to run with parisitic power but it can if needed.
The DS18S20 doesn't, but the DS18S20P also called DS18S20-PAR, only uses "Parasitic Power".

The datasheet ...
http://datasheets.maxim-ic.com/en/ds/DS18S20-PAR.pdf