What ground to use for +5V

[pp42]

I have a NI6601 and I need to use the 5V output to drive an Optocoupler but I cant figure out what to use as ground. Can somebody please help me?
Per

[AnalogKid2DigitalMan]

If you are referring to the PCI-6601 timer/counter card, any of the pins marked GND will work. They are all equivalently connected to the same point within the card.

[pp42]

Sorry for being unclear Yes it is a PCI-6601.
I was confused by D GND and RG both seams to be at 0V, at first I thought that D GND was for the digital line and RG for the “power” line then I thought that D GND was ground for all and then I found some other references that just confused me so I decided to ask all you people.
If some one could explain what RG stands for I might be a little less confused 😉
Per

[AnalogKid2DigitalMan]

Per the manual:

RG: reserved ground. Pins that are marked RG on the I/O connector are
no-connects if you use the SH6868-D1 shielded cable, while they are
ground pins if you use the R6868 unshielded ribbon cable.

You may also want to look at pg 4-22 of the manual if using the SH6868-D1 cable, it talks about twisted pairs and their respective grounds for high speed signals.



Good Luck!

[pp42]

Thanks a lot that clears it up.
Can’t believe that I missed the D GND and RG thing it’s just right there when I look now. I did find the 4-22 page but it says nothing about the twisting for +5V so that is way I asked.
Per