This is digitemp (http://www.digitemp.com) for mips based devices.
This version is from http://www.lecad.uni-lj.si/~leon/other/wlan/wrt54ow/
The schematic is very simple, only a schotky diode and a resitor (but 3 wire):

+3,3V -----------+---------o 3
                 H
                 H 4,7K
                 H
RX --------------+---------o 2
                 |             DS18S20 
TX ---|<---------+

GND -----------------------o 1

Please note: RX/TX are the AD5120 pins. NO RS232 level converter !!

A schemativ for parasite power comes later.