adccommunitymod (AutomationDirect) asked a question.
Created Date: April 28,2005
Created By: Guest
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Here is my setup: PLC450 #1 w/ Ecom PLC450 #2 w/ Ecom EZ-Touch w/ Ethernet Ethernet Switch PLC #1 has an Rx and Wx code to communicate with PLC #2 every other scan. PLC #2 has no rx or wx. EZtouch has read/write for both PLCs. The above is the setup of the PLCs and HMI. Looking at the Ethernet switch and the ECOM modules they are ALWAYS active, blinking crazy. Also, when I hook up the laptop to the ethernet switch, the network card on the laptop goes blinking crazy. Is that activity normal? What's braodcasting that many packets and why broadcsting to the laptop (with the DirectSoft being off). Does this mean I have a faulty Ecom which is broadcasting crazy! I'm running TCP/IP.
Created Date: April 29,2005
Created by: marksji
Its all the EZ-Touch. It will poll your PLCs as frequently as possible.
Created Date: April 29,2005
Created by: hanziou
I understand the the ports on the switch for the PLCs and the EZTouch flashing all the time. But if it is a switch, why is the laptop network card so busy. Isn't the idea of a switch hta it only sends the packets to the ports that have the matching address?
Created Date: April 29,2005
Created by: marksji
yep, but for some reason the EZ-Touch cards seem to broadcast just about everything...
Created Date: May 02,2005
Created by: Guest
I thought the same; if the "Industrial Switch " from AD is a switch, it would limit communication, but that EZ TOUCH is the culprit then.
Any answers from AD techs? Is there a way to limit the broadcasts from EZ Touch?
Thanks
Created Date: May 03,2005
Created by: Tech Guy
As far as I know, no. I will try to explain how the ECOM and EZ-Ethernet work, but I may not have it right.
The broadcast message has to do with the fact that it uses UDP instead of TCP for the packet delivery.
Ethernet packets are made of several 'layers ', UDP and TCP being two of these 'layers '. UDP is a lower leverl layer on top of which the TCP layer resides.
Switches look into the TCP layer in each packet to determine where to send the data. If there is no a TCP layer then the switch is forced to send the packet out as a broadcast message.
Hopefully I have this correct. If not then perhaps HOST Engineering will correct me.
Created Date: May 06,2005
Created by: marksji
I'm pretty sure that your confusing routing with switching... To the best of my knowledge a switch forwards packets based on MAC address; it has nothing to do with TCP/IP/UDP/etc. A router switches data based on IP address, but not MAC address.
Created Date: May 09,2005
Created by: jackson
Why do you say it's broadcasting? I just sniffed my EZ Ethernet to a 405 ECOM and it appears to be unicasting to me.
Granted, it would be nice to have a poll rate option because it is definitely hammering the ECOM really fast.
Ahh...now I see. If you do RX/WX from the 405 ECOM, it is broadcasting.
Created Date: May 09,2005
Created by: Tech Guy
I'm pretty sure that your confusing routing with switching... To the best of my knowledge a switch forwards packets based on MAC address; it has nothing to do with TCP/IP/UDP/etc. A router switches data based on IP address, but not MAC address.
I told you I would get it wrong somehow...
You are correct of course, but UDP is a broadcast protocol. (at least as far as I know)
Created Date: May 09,2005
Created by: marksji
I don't think UDP has to broadcast every packet; I thought it was selectable, broadcast or unicast. It would appear that the EZ-Touch ecoms broadcast everything though (just looking at network traffic).
Created Date: May 09,2005
Created by: jackson
Your EZ Touch Ethernet module is broadcasting? Meaning it is sending packets to a destination IP address of 255.255.255.255?
Mine is not. Mine is unicasting to the specified IP address.
BTW: UDP has nothing to do with broadcast. It is a "connection-less " transport method as opposed to TCP. TCP guarantees that the data gets there. UDP does not.
I believe that the reason you see your switch LED's blinking on all the ports is because of the ECOM's RX/WXs.