BLV: modbus test/setup help

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BLV: modbus test/setup help

Postby om_tech_support_JT » Fri Jan 04, 2013 1:01 pm

Q: I intend to use modbus RTU protocol with your BLV brushless series through RS485 for a new machine design that uses several axes of motion. But before I do that, I need to set up some testing just to prove the concept. I will have to do this test without a master controller/PLC device that can send the modbus commands. Do you recommend any free software I can use on my PC to test the modbus protocol? I'm also having trouble looking for the pin-out diagram of the RJ45 connector. Can you help me set up my initial test?

A: Sure. We have an easy-to-follow guide in our BLV series manual regarding the setup of RS485 communication. Make sure the cover of the manual is labelled, "USER MANUAL (RS-485 Communication Mode)", and the guide starts on page 6 / Chapter 4.

We would suggest a freeware called "ComTest Pro" from Baseblock Software to test your modbus communication. It has worked for us for simple tests. However, since most PCs do not have RS485 communication ports, we use a RS485 to USB converter. If you need one, we would suggest the following converter which has also worked for us in the past: ... B_v1_0.pdf

Here's how you should wire the RJ45 connector for RS485 communication (this is also on page 11 of the same manual):
BLV modbus setup - RJ45 connector pin-out for RS485.jpg
BLV modbus setup - RJ45 connector pin-out for RS485.jpg (202.59 KiB) Viewed 4697 times

Here's a summary of the steps you'll need to complete to successfully communicate with the BLV system:
1. Check the installation and connection - You'll need to connect the motor, the power supply, and the communication (in this case, your PC instead of a master/host controller or PLC).
2. Make sure the dip switches are set properly. In this example, every SW2 switch should be OFF except for #5. Turn #5 on to enable modbus protocol.
BLV modbus setup step 2 set the switches.jpg
BLV modbus setup step 2 set the switches.jpg (125.49 KiB) Viewed 4697 times

3. Turn on power and set communication parameters. Normally, you would set this to match the communication specifications of your host controller/PLC.
4. Cycle the power to update communication parameters.
5. Try a command and test.

If it doesn't work, or if you receive communication errors/alarms, then please verify your wiring, COM port, and communication parameters.
BLV modbus setup - communication specifications.jpg
BLV modbus setup - communication specifications.jpg (143.54 KiB) Viewed 4697 times

Please let us know if you have any questions.

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