Lick detection and reward control occurs over "Byte C" of the 25-pin D didgital IO port on the TDT RZ6.
The RC circuit that manages these input pins can be seen for example in page "Digital IO" of "JansCIpulses2withGround.rcx". Pins C0, C2, C4 are set as inputs for the left, center and right spout respectively.
Pins C1, C3, C5 control the opening of the respective reward spouts. C6 goes high when the program is ready to detect a lick. It can be used for visual feedback with an LED.
Python module TDTspouts.py takes care of interfacing the RCX file to python.