PCB design: DO+AI ground lines?

[ZolkoW]

I'm using a 6221 multi-I/O card (PCI).

I couldn't find anything about the suggested method of connecting the DGND and AIGND lines on the PCB, and which ones to use them..

There's a shielded SCSI cable between the PCB and the PCI card, and nothing else.

Should I connect all the DGND, AIGND lines on the PCB, or only the ones associated with their AI/DO pairs (for example: I'm using the AI0 input belonging to AIGND on PIN67), or maybe it's OK to use only one AIGND and one DGND?

isn't there a risk of building a ground loop, if I connect the DGND and AIGND on my PCB - as they are connected on tha PCI card already?

thanks in advance.

Z.

[Ben_...]

Hello ZolkoW,

the DGND and AIGND are all connected to one GND on the NI PCI-6221.
you could only use one AIGND and one DGND

Best regards

Benjamin

[ZolkoW]

Thank you for the answer!

I couldn't find anything in the manuals about this.. although I suspected that these GND lines must be connected together at the card.

the PCB is under fabrication now anyway, I connected some GND lines together at the SCSI-68 connector, (for safer connection only) and then routed ONE line to the power supply connector.

(this is the method I used in the past, and it worked - I jus wanted to know if there's any better way)

thank you again!

Z.