I'm currently working on a project that entails polling an Emerson ROC 809 from a Prosoft MNET module (Modbus TCP). The issue I am having is that even though I have setup Modbus communications over the Emerson ROC's ethernet port and setup some points with various conversions, I receive nothing but zeroes (0) at the MNET module. Both systems indicate that they are communicating correctly. Would anyone know if I might be overlooking something? I've also used Modscan but nothing shows up there either. Thanks for the help.

 

I don't know the solution to your problem, but be aware that Modbus (all varieties) begin counting their registers at 1 (one), not zero. If you ask for the values at register 0, you will not get an error, but you will get a zero value register.
Dick Caro

===============================================================
Richard H. Caro, CEO, CMC Associates
Certified Automation Professional (ISA)
Buy my books at the ISA Bookstore:
Wireless Networks for Industrial Automation
Automation Network Selection
Consumers Guide to Fieldbus Network Equipment for Process Control
===============================================================

 

Expanding on Dick Caro's comment - if the Emerson docs talk about a register 40001, it might be they really are talking about register #0, with the 40,000 indicating NOT the offset, but that function #3 is used to access the holding register area.

Modbus is a garbage-in-garbage-out system. Asking for the wrong offset can get you zeros, FF's or utter garbage.

 

I assume you use the ROC809 as a slave. You have to configure registers in the ROC. In the Roclink software go to 'Configure', 'Modbus'. Go to the Registers TAB. For digital values use table 1 and/or 2, for analog table 3, 4, 16. These tables are the modbus commands you are using. Fill in the start and end register and assign device parameter. Use a high enough start register. I know '0' as a start register will not work. I normaly use a start register from 100.

For example to assign SFP3,DATA1 up to SFP3,DATA10 to modbus registers 300300-300399 go to table 3, Start register=300, end register=339, Device Parameter SFP3,DATA1, Indexing=Parameter, Conversion=65, Comm Port= All Comm Ports. If you use Indexing=Parameter you will use Device Parameter SFP3,DATA1, SFP3,DATA2, SFP3,DATA3, ... Indexing=Point will give you SFP3,DATA1, SFP4,DATA1, SFP5,DATA1, ... Use conversion=65 for real values. Comm Port can be limited to Ethernet.

 

Thank you all for your input. I believe Koen has pointed out something that I was not aware of. That is the various tables which are available. I'm not at the job site right now but not sure if i had the option of picking which table I need information from. I will check in the morning. If other tables are available, then most likely, this is has been my problem. Again, thanks to all for you time and input.

 

Not sure if you are aware but Emerson offers free tech support for its ROC800 product. You can contact them at [email protected] or you can call 1-800-537-9313.

 

> Not sure if you are aware but Emerson offers free tech support for its ROC800 product.

Prosoft has online and 800 number help too. They are good products.

 

Is there any ROC 809 Simulator?