You are not registered yet. Please click here to register!

plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
Try our online PLC Simulator- FREE.  Click here now to try it.

New Here? Please read this important info!!!

Go Back - Interactive Q & A > - Interactive Q & A > LIVE PLC Questions And Answers

Thread Tools Display Modes
Old April 19th, 2007, 08:46 AM   #1

Gher.aphelion is offline
Join Date: Apr 2007
Location: Barcelona
Posts: 1
Exclamation TSX Premium MODBUS TCP Messaging

Hi all,

I’m developing a critical application in a TSXP574634M Premium Telemecanique processor (With Unity Pro and native Ethernet port). The Ethernet network contains two PLC’s and two PC supervisors with OpenVMS OS.

Both Supervisors are redounded, thus only one supervisor will be active every moment.

The PLC application consists on:

The PLC sends a MODBUS TCP message using WRITE_VAR function to the first Supervisor making sure that previous WRITE_VAR exchange has finished. If first Supervisor is passive, its Ethernet socket is closed, so it does not answer and WRITE_VAR report is 16#0001 (Timeout). Then, the PLC switches the destination of the message in order to send a message to the other Supervisor changing the WRITE_VAR function parameter called Address (Address of the destination entity of the exchange). Then, the second Supervisor is active and answers the MODBUS Request correctly.

Provoking the toggle of both Supervisors, the PLC detects the problem with current Supervisor and switches to the other… and so on.

But, without apparent cause, after a toggle of a Supervisor, sometimes the report of WRITE_VAR sent to the active Supervisor is 16#08FF (i.e. Message Refused / Destination Application error according to Telemecanique technical documents). After that, the PLC tries to send the message to the other Supervisor but it is passive and the WRITE_VAR report is 16#0001 (Timeout). Then, the PLC tries again with active Supervisor and the report is 16#08FF again… this loop never ends and the link between PLC and the active Supervisor is never established.

I used an Ethernet sniffer called ETHEREAL to analyze the Ethernet traffic and I realized that the messages reported as 16#0001 (Timeout) were really sent because appeared in ETHEREAL but the messages reported as 16#08FF did not appear, they did not exit from PLC’s Ethernet port. Somehow or other, it seemed like WRITE_VAR function did not allow to send a message in that moment.

I tried to re-download the project and the application returned to work correctly until another unknown event… then restart the anomaly performance.

I solved the problem updating the PLC Ethernet port firmware. I did dozens of tests with the new Ethernet port firmware and the application became stable… But… three weeks later… the problem has appeared again.

¿Have someone suffered from this kind of problem?

¿Someone knows where is the problem and how can I solve it?

Thanks a lot.

  Reply With Quote
Old July 17th, 2007, 09:42 PM   #2

mjduffy is offline
mjduffy's Avatar
Join Date: Jul 2007
Location: Wollongong
Posts: 3
I had a related problem. The READ_VAR didn't time out so the channel looked like ot was always busy. I ended up having to have my own timeout timer for a transmitted messaged and used a CANCEL instruction to reset the READ_VAR so i could retry.
To err is human, to really foul things up requires a computer.
  Reply With Quote
Jump to Live PLC Question and Answer Forum

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
Mitsubishi Q Series Modbus TCP module QJ71MT91 set up help req'd... Pocko LIVE PLC Questions And Answers 0 July 30th, 2006 03:45 AM
Conection beetwen TSX Premium & PanelView chcortes LIVE PLC Questions And Answers 1 August 5th, 2005 02:15 AM
MODBUS TCP gurus cjh LIVE PLC Questions And Answers 1 August 19th, 2004 07:18 AM
Profibus - Modbus TCP translator ewm3 LIVE PLC Questions And Answers 5 May 7th, 2004 12:31 AM

All times are GMT -4. The time now is 04:58 AM.