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Click PLC Will Not Communicate Across Data Tap

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  • Click PLC Will Not Communicate Across Data Tap

    The scenario is we have a bar code scanner, Click PLC(c0-00dd2-d), wireless serial device server, and cnc control. The wireless serial device server has two serial ports. One is used for communication with the cnc control. The other is used for communication with the Click PLC and bar code scanner. The bar code scanner and Click PLC are connected with a data tap. Now I have wired the connections for the PLC and bar code scanner to use different sets of pins so that the devices can't interfere with each other and wired the out on the tap to combine the transmit pins.

    The problem I have run into is when both the bar code scanner and the Click PLC are connected to the tap only the bar code scanner communications are received. The Click PLC shows that it is transmitting but nothing is ever received by the wireless serial device server. I have tried switching the devices around to verify that both ends of the tap work. Also I have tried only connecting the Click PLC to see what happens and it works when it is connected by itself from both ends of the tap.

    So what I can't figure out is why the Click PLC communications do not get through when both devices are connected. Any suggestions would be much appreciated.

    I could switch to using a modem data splitter, but those cost twice as much.


  • #2
    I'm not sure that I'm understanding exactly how you have it wired, But I would guess that the problem has to do with one of the transmitters pulling the data line high or low relative to the other, and so the device with the least amount of resistance is taking over the data line.
    If you post an actual drawing of how the wiring is hooked up, I/we may be able to help you make it work.

    I think by the time you get this figured out, you will probably understand why the other device costs more.
    Circumstances don't determine who we are, they only reveal it.
    Jason Wolthuis

    Comment



    • #3
      Data Tap Wiring

      Port 1
      pin 1 = nothing
      pin 2 = transmit
      pin 3 = nothing
      pin 4 = nothing
      pin 5 = nothing
      pin 6 = nothing
      pin 7 = nothing
      pin 8 = nothing
      pin 9 = nothing

      Port 2
      pin 1 = nothing
      pin 2 = nothing
      pin 3 = nothing
      pin 4 = nothing
      pin 5 = nothing
      pin 6 = nothing
      pin 7 = nothing
      pin 8 = transmit
      pin 9 = nothing

      Tap
      pin 1 = nothing
      pin 2 = jumped to 8
      pin 3 = nothing
      pin 4 = nothing
      pin 5 = nothing
      pin 6 = nothing
      pin 7 = nothing
      pin 8 = jumped to 2
      pin 9 = nothing

      Comment



      • #4
        The modem splitter costs more, because there is more to it than I need.
        It allows two way communication but isolates each port with diodes so there is no interference between devices.

        I already talked to tech support at the company I bought the tap from so I could try to figure out why this isn't working.

        As long as both devices do not use the same pins the communications should get to the wireless serial device server. However this is not the case so far. Even though they are completely separated only one device's communications get through.

        Comment



        • #5
          You need a gnd. (Signal Ground) terminal connected to both devices somewhere.
          Circumstances don't determine who we are, they only reveal it.
          Jason Wolthuis

          Comment



          • #6
            What pin on the Click PLC do I use for that? Pins 1 and 6 are listed as ground but neither one says signal ground.

            If I need a ground why does one device work?

            Comment



            • #7
              Basically the receiving device is measuring the voltage difference between the signal ground and the receive line. Right now that signal ground is "floating" so when the click transmits, the device trying to read the signal never sees a enough of a difference between the two lines to interpret an "on" signal. When you unhook the scanner, the signal ground drops low enough that it will work.
              I believe that either 1 or 6 can be used for the ground (if in doubt check the manual).
              Circumstances don't determine who we are, they only reveal it.
              Jason Wolthuis

              Comment



              • #8
                Manual is no help. Just lists both as ground. I can try one then the other if the first one doesn't work.

                Comment



                • #9
                  Ok. Tried both grounds and still had the same problem.

                  Comment



                  • #10
                    Please post a link to the Data Tap.
                    If it is one like B&B sells, then what you are doing is trying to reverse what it is designed for, and it won't work like that
                    Circumstances don't determine who we are, they only reveal it.
                    Jason Wolthuis

                    Comment



                    • #11
                      http://www.blackbox.com/Store/Detail...ors-MFM/FA149A

                      Says it's straight through from port 1 to port 2 all pins. Then the tap listens. No communications can go back through the tap to the bar code scanner or PLC, one way only. They don't provide a wiring diagram for the internals.

                      Comment



                      • #12
                        the tap you linked to is a tap... i,e, it will allow you to parallel data flow to a monitoring device. It's not a splitter...

                        Comment



                        • #13
                          Pins 1 and 6 are the same physical ground point inside the PLC. Either will work.
                          If you have an urgent issue, please contact AutomationDirect's Technical Support team.

                          AutomationDirect.com Technical Support: 1(800) 633-0405 or (770) 844-4200 Email Tech Support

                          Comment



                          • #14
                            scott.lawrence that is exactly what I want to do. I want to get data from two devices on one serial port. Data only goes from the devices to the port. I wired the two devices on separate sets of pins then combined them on the other side of the tap. This should allow both devices to use the same port without interfering with each other on the other side.

                            However, only one devices communications are getting through when both are connected to the tap.

                            Comment



                            • #15
                              Thanks for the info ADC App Assist.

                              I will try calling tech support tomorrow. I put in an email already, but I haven't gotten anything back yet.

                              Also, thanks to plcnut for your suggestions.

                              If anyone else has something for me to try or some info I am subscribed to this thread and will be checking my email frequently.

                              Comment

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