Differences between PFI and RTSI synchronization.

[jtipton2]

I'm new to LabVIEW and am trying to sort out some confusion.

I am attempting to simulatenously collect 32 separate voltage measurements. I have at my disposal 2 PCI-6013 cards. After perusing the NI website I came to the conclusion that I needed a RTSI bus in order to synchronize the data collection between the two cards. Unfortunately, I later discovered that the PCI-6013 cards do not support RTSI connection.

I have now found example files in the NI Developer Zone to "Synchronize Two E Series Boards Using PFI or RTSI". One of the files specifically allows one to "synchronize acquisition on both boards using PFI line 7 to share a scan clock signal".

Could someone please help me understand the differences between synchonizing data collection between two cards using PFI and RTSI? I'm hoping that PFI will work since that's all I've got!

Thanks! ~jtipton2

[Hal_L]

Hi

RTSI is an internal timing bus used to share and exchange timing and control signals between multiple boards through the use or parallel digital lines. With RTSI, you can internally connect the two cards with a RTSI cable and you can route the signals in software. RTSI is designed to route internal signals between cards while PFI lines are used to connect cards to external signals. These external signals can include outputs from PFI lines on other cards.

Since your cards do not support RTSI, you can connect the PFI lines externally. You will need to physically connect the PFI lines. You can synchronize your analog inputs by using the same analog input sample clock for both acquisitions. That is what the example on the web is doing.

Regards,
Hal L.

[jtipton2]

Thank you for your reply.

Just to make sure I understand what you are saying, please consider this... I have two NI-6013 cards. Each card has a guaranteed sampling rate of 200 kS/s. I am taking 16 single-ended voltage measurements on each card for a total of 32 measurements.

Is it correct to say, then, that I could achieve a maximum of 400/32 = 12.5 kS/s per channel with RTSI synchronization (if the card supported that) while a PFI synchronization would only allow me 200/32 = 6.25 kS/s per channel?

Thanks! ~ Joe T.

[Hal_L]

Hi Joe,

You will actually have a 12.5kS/s maximum sampling rate per channel with your setup with RTSI or the PFI lines. The 200 kS/s maximum sampling rate is for each individual card. Using the same analog input sample clock to synchronize your acquisition will not affect the maximum sampling rate of the individual cards.

Regards,
Hal L.

[jtipton2]

Hal,

Thanks so much for your help!

Here's one more question and I promise I'm done 🙂 I would like to convince myself that the master device is indeed exporting its timing signal over PFI7. When using an oscilloscope for this test, where should I connect ground? I've already tried the digital ground pins and end up receiving no signal.

~ Joe

[Hal_L]

Hi Joe,

When you are using PFI 7 as the AI sample clock, you will need to use pin 38 (PFI 7/AI sample clock). You can connect this and the digital ground to you oscilloscope to recieve the signal. Another way to verify the sample clock is to connect pin 38 to to an analog input channel and connect the digital ground to the analog input ground. You will then be able to read the AI sample clock on that analog input channel.

Regards,
Hal L.