Dear Lyn
The your NI 6025E board has 32 digital I/O lines - 8 of which are provided by the DAQ-STC chip found on the board (DIO0-7) and the rest (DIO8-31) by an additional 8255 chip on your card (these are the DIOs found on the extended DIO cable.
The DIO lines are conveniently grouped into 8-bit ports such that port 0 = DIO0-7, port 1 = DIO8-15 and so on. Given the number of DIO lines on your board it follows that you have 4 ports, numbered 0 to 3. It's simply a more convenient way if you need to read/write to multiple inputs/outputs. You can make best use of the ports by considering how many inputs and outputs your system will require and group as many like signals on the same port e.g. port 1 contains all inputs. That way when you read port 1 yo
u will get a number relating to the state (HIGH/LOW) of each of the eight DIO lines in the that port. It is a more efficient process than individually reading each line in turn.
A word of caution however. The 8 DIO lines provided by the DAQ-STC can be configured as either an input or an output or mixed e.g. DIO0,1,2,7 = input DIO3,4,5,6 = output. With the ports provided by the 8255, all lines on a single port must be either inputs or outputs - you cannot mix signal direction within a port.
As for the multiple DGNDs, all these pins are taken back to a single reference point on the DAQ board. Therefore you do not necessarily need to use DGND pin corresponding to your signal pin. The multiple DGND pins are there to make your life a bit easier when it comes to wiring!
Jeremy
