85 deg. C is the default power-on state of the temperature reading.
If you get 85 deg. then you are successfully reading the device.
If it stays at 85, then a conversion is not being performed.

Your program works here in the simulator, so it probably comes down to this.

Check the part number on the DS18B20.
If it is followed by a "P" or "PAR", then it's a parasitic power ONLY device.

A parasitic power only device will not perform a conversion if powered like a normal DS18B20.
You must drive the DQ line high for the duration of the conversion for it to complete.