PXI advantage

[levin.hua]

Does anyone know the advantage of PXI system, is there any difference from PC system? or please give some hint for PXI programing.

[Jeff Plotzke]

Does anyone know the advantage of PXI system, is there any difference from PC system? or please give some hint for PXI programing.

A PXI backplane is essentially a PCI bus with added signals for dedicated timing and synchronization. I'd use PXI if you're specifically looking for synchronization between cards. Other than that, and being different form factors, there's nothing else largely different between the two.

PXI systems run either with an embedded controller (which typically run Windows, but could also run an Real-Time OS) or can be linked to a PC using an MXI cable. You'd program in LabVIEW the same you would on a desktop.

Here's a page that describes PXI: http://zone.ni.com/d...a/tut/p/id/4811

[David Wisti]

One advantage PXI has over PC is support for new products. NI always seems to release new products for PXI and may or may not release PCI versions of those products. A perfect example is the R-Series Virtex-5 FPGA cards. There are still no PCI versions of these cards yet

Edited July 8, 2009 by David Wisti

[crelf]

I'd use PXI if you're specifically looking for synchronization between cards. Other than that, and being different form factors, there's nothing else largely different between the two.

That's a really good point. I'm not against PXI (I use it *a lot*), but I've often quizzed engineers on why they are using PXI over PCI, and the blank "because NI says it's better" stares I get back make me shake my head. It's a good form-factor (can get cards in and out more easily than a PC, depending on your access to the PC - think rack builds) and the synchronisation kicks arse - if you don't need either of those features, then you're probably wasting your money. Also, there are some cards that are only available in PXI or PCI format, so that's a factor to consider too... In that case, it might be wise to consider a PCI-based PC with an MXI link to an external PXI chassis (we do that a lot too).

One advantage PXI has over PC is support for new products.

I already mentioned MXI, but there are carriers out there that allow you to put PCI cards in PXI chassis, and PXI cards in PCI PCs. I've done the former with great success before, but only ever tried the latter with an MXI link.

[Jeff Plotzke]

...the synchronisation kicks arse...

Another note is that you can take most PCI DAQ cards and use a RTSI cable between them to add the synchronization layer that PXI provides. It's the poor man's PXI and doesn't give you the convenient form factor PXI provides, but allows you to do synchronization between your DAQ cards on a desktop.

What is RTSI: http://digital.ni.com/public.nsf/allkb/A120195AAAA9222A86256C69007C8B27

[crelf]

It's the poor man's PXI and doesn't give you the convenient form factor PXI provides, but allows you to do synchronization between your DAQ cards on a desktop.

Yes and no - it allows for synchronisation, but doesn't have things like the common-length trigger paths that PXI has. It's not a direct replacement for PXI sunchronization functionality, but it's pretty good at what it does.

[JustinThomas]

PXI based hardware is available from a large number of vendors. The official PXI system alliance website www.pxisa.org

[crelf]

PXI based hardware is available from a large number of vendors. The official PXI system alliance website www.pxisa.org

That's a really great point - we generally used NI hardware because we know it works and it integrates well with our development environments and established architectures. If a particular need for a card outside of NI's range comes up, we're okay with using a 3rd party vendor's PXI cards, as long as integration is relatively straight forward (eg: Pickering have some great switch cards that are IVI compatible, so they work with NI-Switch). Another thing to remember is that CPCI (Compact PCI) cards will work in PXI chasses too (eg: the PXI-GPIB card from NI isn't actually PXI, it's cPCI), so as long as you have the drivers, you're golden.

[Gary Rubin]

There are still no PCI versions of these cards yet

I agree with that frowny-face. We were looking at a Flex-RIO card for an application. The card's capabilities would be perfect, but the fact that we'd have to add a PXI box is a problem.

CRelf, can you point to any of these PXI-to-PCI adapters you're talking about? I think I've seen such things for 6U cPCI, where the card cPCI card sticks up like a double-height PCI card (and you can't put the lid on the compuer). Is that what you're talking about?

[crelf]

CRelf, can you point to any of these PXI-to-PCI adapters you're talking about? I think I've seen such things for 6U cPCI, where the card cPCI card sticks up like a double-height PCI card (and you can't put the lid on the compuer). Is that what you're talking about?

I knew someone was going to ask! I don't remember where I got it from, but I remember it took me days to find it Sorry I don't have any details - it was several years ago...

As a side note, whenever I needed to put PCI cards into a PXI chassis, I've used 6U PXI carries inside of the NI 3U/6U PXI Combo chassis. I don't think a 3U PXI PCI carrier exists (I'm happy to be proven wrong).

[JohnRH]

Does anyone know the advantage of PXI system, is there any difference from PC system? or please give some hint for PXI programing.

Bottom line for us is often just the physical requirement of how many cards we need to fit in a chassis. If it is more than 2-3, then PXI is once of the simplest options.

(although I have used 20 slot PCI rackmount PC's as well, saving a pretty penny when using over 50 chassis for one test system)

[crelf]

...using over 50 chassis for one test system...

I'd love to see a photo of a 50 chassis system!

[JohnRH]

I'd love to see a photo of a 50 chassis system!

It was something like 19 racks. It took up almost an entire room. (not to mention 50kW of power)

It was also a sore point for NI because they REALLY wanted us to use PXI.

Edited July 9, 2009 by JohnRH

[levin.hua]

In my little brain, i just feel PXI is expensive one and most of them can be replaced by PCI. A stupid question, if we use MXI to connect PXI to PC, should PXI system install OS? Is there any special requirements for PXI system install OS, like driver, configuration......?

[i2dx]

In my little brain, i just feel PXI is expensive one and most of them can be replaced by PCI. A stupid question, if we use MXI to connect PXI to PC, should PXI system install OS? Is there any special requirements for PXI system install OS, like driver, configuration......?

no. MXI is more or less "just" a extension of the PCI-Bus of your host-system. If you want a OS on your PXI (and write RealTime applications) you need a controler.

[memoryleak]

I don't know what the "official" word is, but here are some thoughts from a hardware design perspective. They may not be good reasons, and they may not even necessarily be correct.

1) There are requirements on how much power we're allowed to draw from a PXI slot (I'm unsure how it compares to power from a PCI slot, but I would assume it is more because some PCI/PCIe cards require an extra power plug that their PXI cousins do not). Additionally, there are requirements on the chassis as to how much power they *must* be able provide to us.

This means that when you drop $10k for a brand spankin new top-of-the-line oscope, you know that you wont have to worry about whether or not the overburdened power supply in your dusty 5 year old dev machine can handle it.

2) There are some requirements as to how much cooling each slot in a PXI chassis will get, whereas PCI slots are more of a crapshoot. It's possible to design a computer tower to have a rediculous amount of cooling for your PCI slots, but more likely you have an 80mm fan or two nowhere near your cards.

Some devices, like high resolution DMMs, are heavily affected by the ambient temperature.

3) I'm pretty sure PXI is slightly wider, allowing for more space for components and such.

4) You can buy an 18 slot PXI chassis. Just try and find a motherboard with 18 PCI slots

5) RTSI cables are great for synchronization, but I believe there is a limit (due to signal integrity) of how many devices you can chain together. I'm also pretty sure that limit is less than 18.

I'm sure there are more reasons than this, but these came to mind. That said, I currently own two NI PCIe cards and I love them to bits.

Hugs,

memoryleak

Full disclosure: I'm sitting at my desk on the 6th floor of NI building C right now.

P.S. surely there is a way to tag myself as being someone who is "drinking the koolaid"

[crelf]

Full disclosure: I'm sitting at my desk on the 6th floor of NI building C right now.

Welcome Blake - great to have you here!

P.S. surely there is a way to tag myself as being someone who is "drinking the koolaid"

I've added you to the NI group - should show up as such soon.