TRIG IN and TRIG OUT on VXI-MXI-2

[gberry]

It appears from the register definitions on the VXI-MXI-2 board there is no way to route TRIG-IN and TRIG-OUT to the same internal trigger line. Is this correct?
What about if you use 2 chassis with 2 VXI-MXI-2 cards?

[Dustin_W]

What is it that you are trying to accomplish? TRIG-IN is used only as an input, and TRIG-OUT is used only as an output. The internal trigger line can only go one direction, so it makes sense that it can only be connected to one or the other. If you use 2 chassis, you could concievably read the trigger input on one chassis, and then write to the output of the other chassis, but you cannot connect them to the same internal trigger line still.

[gberry]

I am trying to route triggers through a system with multiple chassis. What I had imagined was that the TRIG-IN and TRIG-OUT had seperate multiplexer circuits, such that each could attach to any trigger line. The idea being if you set TRIG-IN to say TTL0 and TRIG-OUT to TTL-0, the VXI backplane would get the trigger pulse as well as echoing it to the TRIG-OUT. It looks like the PXI-6653 has this ability, which is where I originally got the idea...

As for the two chasis configuration, on chassis A, I could set TRIG-IN to TTL0. On chassis B, I would set TRIG-OUT to TTL0. I would then route TTL0 "out" on the MXI bus on the chassis A VXI-MXI controller, and route TTL0 "in" on the MXI bus on the chassis B VXI-MXI controller. I was wondering if this would work..
.

[Josh_KNH]

Hi gberry,

Just to clarify your situation, you want to share an externally generated trigger between two VXI chassis that are connected via MXI-2? Is this correct?

In this situation, the easiest setup may be to bring the trigger in through Trig-In on the VXI-MXI-2 in chassis A, and then route the trigger across the MXI bus to chassis B. MXI-2 routes both the data bus and VXI signals like triggers and interrupts, so you don't necessarily need to bring the trigger signal out of the system again. If we're still not understanding each other, please feel free to clarify. Otherwise, you can setup the routing from one chassis to another in Measurement and Automation Explorer.

KnowledgeBase 2BUEGE58: How to Map Triggers Using VXI-MXI-2 and NI-VXI

Best Regards,
Josh Hernstrom
PXI/VXI Product Support Engineer
National Instruments

[gberry]

Hi Josh,

Yes you are correct. I already plan on routing the triggers across the MXI bus. The design involves three chassis, not just two. Not only that, I need to trigger non-VXI products too. I have more than one external trigger source I need to use. I hoped to use the TRIG-INs and TRIG-OUTs to multiplex my external trigger sources. This way I could steer the chosen external triggers to the non-VXI products. This is why I wanted to get the TRIG-OUT and the TRIG-IN on the same line internal trigger.

This poses another question about the trigger routing through the MXI bus. Since it is directional, if I have a trigger source on chassis A and a trigger sink on chassis B, then I am going to have to reroute the trigger if I have a tri
gger source on chassis B and a trigger sink on chassis A? I assume the answer expands to the three chassis case as well...

-Greg

[Josh_KNH]

Hi Greg,

Thanks for the additional explanation on your situation. I noticed in your first post that you are basing your conclusions off the the register map for the VXI-MXI-2. Are you doing register level programming, or are you planning to use one of the existing NI-VXI drivers?

If you use NI-VXI, it already contains support for what you would like to do. For example with the VXI API, using the function MapTrigToTrig(), you can simply route from Trig-In to a TTL line. Calling the function again, you can route from that same TTL line back to Trig-Out. This should work, but it may not be evident simply by reading the register map for the VXI-MXI-2 because it's possible that the registers used in this situation are not document
ed in your reference (what register map reference are you using?).

Josh Hernstrom
PXI/VXI Product Support Engineer
National Instruments

[gberry]

Hi Josh:

I am using NI-VISA drivers, but I wanted to map the MXI triggers and TRIG-IN and out from software calls. I started looking at the following documents:

VXI-MXI-2 users manual: http://www.ni.com/pdf/manuals/321003b.pdf (chapter 5)
Specifically registers: VTCR, VUCR, VMCR, VLAR, VTDR, VTMSR, VMTCR

High Level Register access example:
ftp://ftp.ni.com/contrib/epd/B45EACE3DA7056A4E034080020E74861/High_Level_Register_Access_with_NI_VISA.zip

and later I found:
http://www.ni.com/pdf/manuals/370132c.pdf
But I was concerned about the "Note" on page 5-63 (253 of 423) Since the registers only enable and have a direction, this seems to indicate I could map multiple signals to TRIG-IN or TRIG-OUT, but never bot
h at the same time.

I am in the process of writing some test code. I might attempt the TRIG-IN/TRIG-OUT from the VISA call, but this still leaves me wondering how to map the MXI trigger lines without using a GUI.

-Greg

[Josh_KNH]

Hi Greg,

On the first issue, for routing from TRIG-IN -> backplane and backplane -> TRIG-OUT, this should work with NI-VISA as you plan to test. The "Note" you pointed out in the NI-VISA Programmers Reference Manual on page 5-63 refers indirectly to certain obsolete products. One example is the older VXI-MXI-1 products. VXI-MXI-2 should work fine for what you are trying to do.

On the second issue, you can programmatically route triggers across the MXI bus to a second chassis using one of the registers you noted above. Use register VTCR to perform this programmatically. VTCR, VXI TTL Trigger Configuration Register, is a VXI-6 compliant register. The other registers may expose similar functionality in differe
nt ways, but VTCR is part of the VXI spec. and thus much less likely to ever change.

Cheers,
Josh