Modbus TCP
Modbus TCP
(OP)
I am working on a SCADA system upgrade and the owner wants to use Modbus protocol on an ethernet radio network. I am having trouble finding any useful information on Modbus TCP protocol. Does anyone know of any good websites/documents which could help me out? I'm mostly looking for a list of features, specifically whether it supports multiple masters, peer to peer operations (submasters), time stamped events or unsolicited messaging.
I know modbus RTU does not support a lot of these things, but I am looking specifically at modbus TCP.
Thanks for your help!
I know modbus RTU does not support a lot of these things, but I am looking specifically at modbus TCP.
Thanks for your help!





RE: Modbus TCP
zapsib
RE: Modbus TCP
Modbus plus does support multiple masters but is limited to those vendors who license the technology.
Modicon and Schneider supports Modbus Plus.
http://www.modicon.com/opennetworking/modbus/
RE: Modbus TCP
I base my impressions on the fact that the commands that were transmitted and received were standard Modbus RTU and they used a combination of ethernet switches and ethernet - rs485 converters for the devices that only supported rs485.
RE: Modbus TCP
RE: Modbus TCP
Try Software Toolbox's TopServer or Wonderware's Modbus ethernet
RE: Modbus TCP
The limitation comes from your choice of radios. Some radio transceivers only support one master on the network. Others work in a peer-to-peer fashion allowing any station to initiate a conversation. In the former, you can still setup any of your stations to generate a master poll but this all depends on how 'mastering' is implemented in the device in question.
I know of some native Modbus PLCs that are setup as 'masters' in the logic. As a result, you can have multiple of these PLCs polling each other, in effect having a multiple masters in your Modbus network. Even with radios that do not support multiple mastering, these PLCs were still able to poll each other.
Klaus
RE: Modbus TCP
I have actually long since solved this problem, but hopefully other people can benefeit from the later posts.
What I used was Modbus TCP using MDS iNet radios transmitting to a MDS 5 series redundant backbone ring. I used all SCADAPack RTUs and front end and the multiple master, unsolicite dmessaging, and peer to peer communications is working like a charm, it turned out I didn't use the time stamping, but I'm sure I could have programmed something if I wanted to. The SCADAPack MSIP function allows pretty much all of this functionality, as long as the correct timing and error checking is set up to ensure there is not too many connections to one RTU.
Using the ethernet radios makes things so easy, doing this over serial would have been possible, but a fair bit more work.
RE: Modbus TCP