USB-6346 SPI and PWM?

[MichaelBoyte]

I am having to find an alternative to a cRIO system and I think I may have found what I need in the USB-6346, but I am having trouble finding direct answers to some questions I have. I need to know if the USB-6346 can communicate with several modules over SPI and can it send out at least two PWM signals to control some motors? If not, are any of the other USB-63## modules more suited to this task? In all, it needs to communicate with four SPI modules, read two analog voltage inputs, output two PWM signals, and preferably have a couple general use DIO pins left over.

[santo_13]

Implementing SPI on 6346 is not easy as you would have to do bit-bang implementation on the software, instead, it is easier to use the USB-8452 to do the SPI communication and use the 6346 just for PWM/DO/AI/AO.

[MichaelBoyte]

Thank you for the quick response. This will be a closed-loop system in which the PWM signal will be directly related to the data received from the SPI modules. Would using two USB modules be a problem? Sorry if these are basic questions.

[santo_13]

If this is supposed to be closed-loop systems, using a Windows-based DAQ system will add delay in the loop speed compared to something implemented on cRIO with RT+FPGA.

IMHO, I would reconsider going back to cRIO if this is going to be a closed-loop system. Please provide more information about the application and what is your expected response time for the loop so that other forum users can weigh in their perspectives.

[MichaelBoyte]

I can't go into too much detail, but the system will be dampening out movement oscillating at frequencies less than about 100 Hz. The SPI modules detect the movement and the PWM controls a motor to cancel out the movement. I need to be able to receive SPI data and send out the corresponding required PWM in about 200 us.

Unfortunately for reasons outside of our control cRIO is no longer an option for us.

[santo_13 · Accepted solution]

200us resolution guaranteed response time is NOT POSSIBLE on a Windows OS. Just the driver layer overheads are going to be more than 200us. You might have to re-evaluate your options.

[RIObotics]

Just curious, why is the CompactRIO no longer an option for you?  Availability?  Price?  Functionality?

[MichaelBoyte]

Availability. We wouldn't be able to get it for about a year.

[RIObotics]

Hmm, makes sense.  Seems like there are CompactRIO shortages everywhere.  Have you considered migrating your application to sbRIO?  Usually there is a matching sbRIO product for each cRIO CPU and FPGA gate size.  As long as you weren't using a specialty cRIO module, most I/O functionality can be reproduced on the sbRIO.  For the SPI and PWM signals you need, you can use the DIO lines on the sbRIO, and NI provides LabVIEW FPGA shipping examples for implementing these interfaces.

[MichaelBoyte]

Thank you! I had not heard of sbRIO and so far it looks like it might be exactly what I need.