On the software level, the rising and falling edges are independent channels. In the Graphical User Interfaces, Time Tagger Lab, the rising and falling edges are marked explicitly with a pictogram. In the software libraries, the number of a falling edge channel is a negative number of the physical input. For example, the rising and falling edges of the physical input 2 correspond to the software channels 2 and -2, respectively. You can also use the method getInvertedChannel() to find the inverted channel number for your specific hardware revision.
*Time Taggers delivered before mid-2018 had different channel labeling scheme.