Modbus TCP node regarding points

General
1

Hello,

I have few queries as below.

  1. How many numbers of Modbus TCP slave devices we can connect to Modbus TCP Client node?
  2. How much data size/parameters can we read/write in Modbus TCP node?
  3. Can we configure multiple read command in single Modbus read node? (pls give a count size).
  4. If we configured multiple read commands will it affect on poll rate/response?

I got some information on this topic issue - Sending multiple modbus data values to SQL Server (Azure) in one stored procedure - #2 by Steve-Mcl

Br,
Devendra

2

Google is your friend (but for the benefit of readers: there is no limit to the number of ModBus TCP devices - apart from IP address space)

Around 100 WORDS (200 bytes)
I wrote up the reason for this in another post - but for simplicity sake, dont poll more than 100 WORDS

Dont think so

Yes, but over TCP that is less of an issue that Serial/RTU

3

The Flex Getter node is passed the address to read in the message, so it can be used to read from different addresses.

4

Hello,

Thanks for your response.

Around 100 WORDS (200 bytes)
I wrote up the reason for this in another post - but for simplicity sake, dont poll more than 100 WORDS
-- Do you mean we can read only 100 words in single Modbus read node or overall Modbus application. because I want to read 10000+ tags.

Br,
Devendra

5

Max 100 words in any single modbus read operation. Also see my post above about the flex getter node, in case you missed it as we both posted at the same time.

6

Hello,

So do you mean 1 single Modbus read node support 100 words only, then If we want to read next 100 words in that case I have to add 2nd Modbus read node is correct? and same if we want to read more 100 words so I need to add 3rd Modbus read node correct? e

Because data is too much more than 10000+ words.

Br,
Devendra

7

It depends what you mean by 'modbus read node'. If you mean the node type Modbus Read
image
Then yes, you would need multiple read nodes. However, as I have said several times, if you use the Flex Getter node
image
then you can pass the address in the message, so you can use the same node to get as many different addresses as you want by polling it multiple times with different addresses.

8

ModBus has this limitation (not-node-red)
The limit is actually 125 WORDS read, 123 WORDS write (but I generally tell people to stick with 100 WORDS

What PLCs are you communicating to?

Are modbus devices connected to PLCs or do you intend on accessing the actual devices individually? I ask many modbus devices only have a handfull of useful (runtime) addresses anyhow.

9

Thanks for your supports to clarifying my doubts.

Br,
Devendra

10

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