Modbus question

Got a PM from a user "shwe", thought it should be a thread instead:

I need a help from you
As i am beginner please help me in understanding Modbus TCP/IP v/s UDP

Why do we need to convert RS485 to TCP

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RS485 conversion is completely different to the TCP vs UDP question. What are you trying to do?

RS-485 is one of the physical links used by Modbus RTU. RS-233 is the other.

Modbus/TCP is widely used over Ethernet.

There are few, if any commercial implementations of Modbus/UDP.

If you want to experiment with Modbus UPD, see this link
http://jamod.sourceforge.net/kbase/modbus_udp.html#Protocol+&+Speci

Don't expect support, because Modbus UDP is not the standard.

sorry... just had to...

Came across this, seems appropriate

I am surprised to hear all these Modbus UDP conversations lately and not just in this forum, I hear that from other sources.
Is this all coming forum the same user (or company) who is trying to push something?
As pointed above, this is not something standard.
It’s not a big deal to write transport from TCP to UDP, there is a bigger issue.
While UDP will reduce overhead of handshaking, my big concern is how implementer should handle timeouts?
For example, with EtherNet/IP it’s clearly defined as 4x RPI and minimum 100ms. Both devices will monitor and enforce that.
How this will be handled with ModBus UDP since there is not standard?
It means that every vendor will try to make it’s own..
So what will happen when devices start talking?

I think your conclusion is correct - every vendor different.


My, what a joy! ! !


Dan

There is no such animal as Modbus UDP. Just about any serial protocol can be encapsulated in UDP (or TCP). Typically you have a terminal server on each end to encapsulate and unencapsulate the serial data, but that's not required.

KirkC said:

There is no such animal as Modbus UDP.

Click to expand...

The link I had posted above has source code for such.

Yes, there is no 'Standard' for Modbus/UDP, and for reasons I don't comprehend, people seem to want to mess with it; hence the questions that pop up.

Me - I stick to conventional. No time to mess proprietary diversions.