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AdisharrAdisharr Posts: 6 Apprentice
Hi All,

I'm currently using a WAGO Modbus TCP fieldbus coupler (750-352) with a UR5e robot and am seeing some strange behavior. I current have (2) 8 pt input modules and (2) 8 pt output modules attached.

I'm using 15 inputs with Modbus addresses 0-14

I'm using 9 outputs with Modbus addresses 0-5 and 8-10

It mostly works fine but the outputs seem to interfere with each other. One example, when the system boots up, the output on Modbus address 2 is 'on' but not actually on. It will not actually turn on unless I go into the I/O screen and turn it off and then on again. That's of course not ideal asking my customer to do that when they start their robot.

I think I have the addressing correct - that seems fairly straight forward. Anything I might be missing?

P.S. I have most update rates set at 5 or 10 Hz but two things set at 25 Hz to get a bit faster response from them.


  • matthewd92matthewd92 Founding Pro, Tactile Sensor Beta Testers Posts: 1,267 Handy
    Do you mean when you boot-up the robot or boot the WAGO unit?
  • AdisharrAdisharr Posts: 6 Apprentice
    edited August 2019
    Hi Matt,

    Generally the main panel boots up (with the WAGO unit) and then the robot is powered on with it's front panel pendant button. I can reboot the robot, reload the robot program and still see the same behavior. I'll still need to go into the I/O screen (where it shows that output being on) and manually toggle it off and then on for it to actually go on.

    I've heard historically that the Modbus client interface is a big buggy. I'm not sure if I need to set up the bus coupler in a slightly different configuration.
  • matthewd92matthewd92 Founding Pro, Tactile Sensor Beta Testers Posts: 1,267 Handy
    Yes, that is a true statement but I’ve never seen this behavior. We haven’t used a WAGO bus coupler since 2014 but I don’t recall having that issue. We use the Turck TBEN multi-protocol IO blocks and have never seen that issue with them. I’d check to see if there are any settings on the WAGO you can change. Is it just that output or any of them?
  • David_GouffeDavid_Gouffe Vacuum Beta tester Posts: 56 Handy

    I do not have a WAGO remote IO Modbus fieldbus coupler. 

    But I think I can guess what happened to you:
    The I/O are probably at the last value they had the last time they changed. This viewed by the WAGO Module. 

    The idea is that at boot you probably need to update all your remote IO to really control the actual state of each of them. 

    Not ideal but can occur if the master is not refreshing the output at boot. Might be normal behaviour for Modbus. 

    Hope this helps a little.  


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  • matthewd92matthewd92 Founding Pro, Tactile Sensor Beta Testers Posts: 1,267 Handy
    @David_Gouffe not sure what you mean, we use Modbus on most cells and do not need to toggle outputs at bootup of the robot or modbus unit to get them to be correctly represented on the modbus unit. I think this may be a setting in the WAGO unit itself. 

    @Adisharr I would recommend making sure that you are not using watchdog timers on the WAGO unit. I know the Beckhoff and Automation Direct units use them and that causes a lot of issues until they are disabled. 
  • AdisharrAdisharr Posts: 6 Apprentice
    Thanks for your help Matthew and David. I actually misread the Modbus addressing. Turns out the outputs should start at 512. Interestingly enough, the WAGO unit still mostly functioned with some bizarre behavior. Something to keep in mind should you ever use one. Seems to run just fine now.

    I also checked the watchdog timers and they were off. I completely disabled all ports and the other features in the unit just in case something else was interfering at the time but it was the addressing.
  • matthewd92matthewd92 Founding Pro, Tactile Sensor Beta Testers Posts: 1,267 Handy
    edited August 2019
    @Adisharr now that you say that I remember that from when we used the WAGO unit, only one I’ve ever used that had to be addressed that way.  Glad you were able to work it out. 
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