If you are doing digital input, you do not need to distinguish between counter lines and digital lines. You can read from any line by using the digital read functions. DIG_In_Line, DIG_In_Prt, DIG_Line_Config, DIG_Out_Line, DIG_Out_Prt, and DIG_Prt_Config all work with the 6602, the port parameter should be '0' and possible lines to use are 0 to 31, the directions of the lines are configurable on a per line basis.
If you want to use the programmable function input (PFI) lines for digital output, then you can configure them for digital output on a line-by-line basis.
In the C application programming interface (API), you can use the DIG_Line_Config function to configure the lines individually as output, and you can use the DIG_Out_Line function to perform the ou
tput.
Make sure you have the port set to 0. If this does not work, let me know.
Brian