adccommunitymod (AutomationDirect) asked a question.
Created Date: December 11,2013
Created By: jayjohnsonuga
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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.
Created Date: December 11,2013
Created by: plcnut
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. ;)
Created Date: December 11,2013
Created by: jayjohnsonuga
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
Created Date: December 11,2013
Created by: jayjohnsonuga
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.
Created Date: December 11,2013
Created by: plcnut
You need a gnd. (Signal Ground) terminal connected to both devices somewhere.
Created Date: December 11,2013
Created by: jayjohnsonuga
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?
Created Date: December 11,2013
Created by: plcnut
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).
Created Date: December 11,2013
Created by: jayjohnsonuga
Manual is no help. Just lists both as ground. I can try one then the other if the first one doesn't work.
Created Date: December 11,2013
Created by: jayjohnsonuga
Ok. Tried both grounds and still had the same problem.
Created Date: December 11,2013
Created by: plcnut
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
Created Date: December 11,2013
Created by: jayjohnsonuga
http://www.blackbox.com/Store/Detail.aspx/Data-Tap-DB9-3-DB9-Connectors-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.