The information here is mostly obsolete. Easiest way to check this is opening the MachineDataFile in a text editor. Dev1 is the auxiliary board, PCIe-6323 controlling the Piezo and the Pockels cell, receiving external trigger. Dev2 is the imaging board, PCI-6110 controlling the scanners and receiving PMT output.
Our single NI 6110 S series board is connected via a BNC2110 to the various inputs and outputs required to control, synchronise and acquire data on the 2P system.
The details from the ScanImage docs are here but I always find them indigestible.
For triggering, there are 2 modes: external and internal. In either case a wire has to relay a signal to a digital input pin on the DAC board. For internal triggering, ScanImage generates a pulse on one of the digital outs (which must therefore be connected to an input port – usually just by a little patch wire). For external triggering, the trigger must be connected to a BNC on the board, which in turn must be “patched” with some wire to a digital input.