I would like to use a NI 9871 module with NI veristand to communicate with some devices over RS485 using modbus protocol. I know that this device can be used in scan mode and VISA commands, but will not work with the EtherCat Scan Engine custom device. I am wondering the best method to modify NI veristand. 1. Create custom FPGA personality and write the drivers to directly interface with the ports on the device by modifying cRIO Modbus.lvproject http://www.ni.com/example/31166/en/. Expose the commmands as channels passed from the FPGA personality to the workspace and command those from the workspace.Current limitation, I am unsure how to modify this into a custom device or model due to the FPGA IRQ in the RT application used for timing. Can this be included in the custom device? 2. Use the 9871 in scan-mode and write a custom device to interact with it using VISA command. Deploy Modbus I/O servier in custom device and send commands to shared variables from workspace. This would be easier and more robust driver, but I am unsure how to implement if my other 7 modules are using the scan engine custom device. I cannot implement this one in scan mode and the other seven in FPGA because of only 3 DMA. 3. Modify the Scan engine custom device to support 9871? Not sure if this is possible. Thanks, Mike 4. Not use the NI 9871, and use the serial port on the Crio with a custom modbus device. This leads to a timing issue as I have five devices that I would like to interact with from one port. May reduce functionality.

An update, since I found a method that worked pretty well and was easier than I expected. If you are using the cRIO in scan mode with the scan engine custom device, the ports will show up in MAX for the 9871 module. I didn't realize this when I initially started the post above. From there you can utilize all the functions of the ports similar to the rs232 port that is included on the NI 9074. I wrote a custom device that opened a VISA session to my port and then was able to implement the code I needed to communicate with my rs485 device. I was using modbus protocol and all of the functions worked inside of my custom device with no modification. I could also adjust the VISA settings in MAX and could run a VI from my pc that would send/recieve data to the ports. This will be useful as an additional way to test/change parameters on my rs485 devices outside of NIVS. One thing to note from my last post, deploying a Modbus library did not work. The shared variables from Veristand would not work correctly with the variables as they were configured in the modbus library that I deployed. I was able to manually set them from the distributed system manager. I could also make the variables standard shared variables and they would update from the NIVS workspace in the distributed systems manager, but would not change the value in the modbus server. I decided to ditch this and create a custom device that just used VISA vs. the shared variables.

VeriStand

NI 9871 best way to create customization to veristand

Solved!

Hi ARLROB,

This thread is more than a year old. Please post your question in a new thread, and I'm sure our community will have some ideas.

Message 11 of 11

(1,142 Views)

VeriStand

NI 9871 best way to create customization to veristand

Re: NI 9871 best way to create customization to veristand