NI DAQCARD 16XE-AI-50 misbehaves with legacy drivers

[Strangers+Friends]

I am using the NI Daqcard AI-16XE-50 with legacy drivers in LabVIEW 8.0 to do digital output. When I output four zeros on for digital output ports, four zeros are transmitted.  But when I output zeros on three lines and a one on the fourth line, there is noise coupled from the fourth line onto one of the other three lines, which should receive zeros only. What happens is one of these lines, aserial clock input, that should receive a clean zero signal is instead receive spikes on top of the zero. Is this due to inherent noise in the Write to Digital Port.vi, so that whenever a one is output on a digital line, the zero to one transition on the one line causes noise on the other lines to appear as ones temporarily? I have a serial clock input to a DAC that should be quiet, but is picking up ones when a zero to one on another digital line is asserted. Can this problem be alleviated by using twisted pairs, or by choosing another line out of the eight of the digital output port, with another line being isolated more from the digital line that I am making the zero to one transition on? Right now, I am using a six inch multiline cable to transmit digital signals from the  laptop PCMCIA slot to a multipin connector block.  Then from the connector block I run ground and four untwisted, unshielded wires for my four digital outputs over a length of about three feet to a MAX534 serial DAC with inputs of Chip Select NOT, Digital In, and Serial Clock, and a fourth line used to turn on and off an analog switch, with this fourth line having a zero to one transition that is apparently be coupled to the Serial Clock line.  Do you have any suggestions on ways I can shield my digital serial clock line from picking up noise?

[CharlesD]

Hello I will try to address some of your issues 1 by 1 as such I've copied your post

I am using the NI Daqcard AI-16XE-50 with legacy drivers in LabVIEW 8.0 to do digital output. When I output four zeros on for digital output ports, four zeros are transmitted. 

But when I output zeros on three lines and a one on the fourth line, there is noise coupled from the fourth line onto one of the other three lines, which should receive zeros only. What happens is one of these lines, aserial clock input, that should receive a clean zero signal is instead receive spikes on top of the zero.

1.Is this due to inherent noise in the Write to Digital Port.vi, so that whenever a one is output on a digital line, the zero to one transition on the one line causes noise on the other lines to appear as ones temporarily?

I doubt that this is the cause, it is more likely an issue on the hardware and less likely a problem with the driver call or Labview Function.

I have a serial clock input to a DAC that should be quiet, but is picking up ones when a zero to one on another digital line is asserted.

2. Can this problem be alleviated by using twisted pairs, or by choosing another line out of the eight of the digital output port, with another line being isolated more from the digital line that I am making the zero to one transition on?

There really isn't any other line that will be "more isolated" than the other.  They are all on the same port and therefore should all behave similarly.  Let's try connecting the signal to another digital line and try to isolate the issue to one single digital line.  It is possible that one of the lines is defective.

Twisted pair wires would help if you are experiencing noise from the environment.  This looks like the noise is coming in from another digital line on the card and not from the environment itself.

Right now, I am using a six inch multiline cable to transmit digital signals from the  laptop PCMCIA slot to a multipin connector block.  Then from the connector block I run ground and four untwisted, unshielded wires for my four digital outputs over a length of about three feet to a MAX534 serial DAC with inputs of Chip Select NOT, Digital In, and Serial Clock, and a fourth line used to turn on and off an analog switch, with this fourth line having a zero to one transition that is apparently be coupled to the Serial Clock line. 

3. Do you have any suggestions on ways I can shield my digital serial clock line from picking up noise?

Has this application ever worked properly?  if so what has changed since then? 

Have you tried a different board?  Does it behave the same way?  Let's try different Lines and see if the noise goes away.

The following article has very good information relating to noise considerations.  I suggest reading through it and seeing if anything applies to your particular situation: https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...