Thank you for your time.

Hello,

CezarAdrian

Hello everyone,

I want to use the Modbus TCP function to achieve communication between 4 (S7 -1214C PLCs ) with one in the center (like a brain). I need to read all the information from the other 3 PLC's and send commands to the other 3 PLCs.

What function should I use on this PLC to define all communication at the same time? Client block or server block?

Thank you for your time.

both, logically On your 'brain' Client PLC you need use CLIENT block and at all other PLCs SERVER block. I expect you'll step to quite complex cfg (as connections,...) I recommend for first improve knowledge about TCP networks and especially Modbus protocol.

Hi Cezar,

In this case your "Brain" CPU will act as Client and other three PLCs will act as servers. The client will be initiating the communication and will be able to read and write data to servers. So you need to add MB_Client block in your main (Brain) PLC (Separate MB_Client block required for individual devices, you need to add 3 MB_Client blocks in your main PLC for the 3 servers). In the other PLCs, you need to add MB_Server blocks.

And as Duris said gather some knowledge about Modbus TCP before start working, which will help you with future projects. Attached Siemens Modbus TCP manual for your reference.

Regards

Hello,

possibilities are existed because all depends to actual free connection resources at actual HW and requirements about exact direct HWs connection. It is not common to do inter HWs MB TCP/RTU connections that each station has conenction to only one other device on network. Phantasy

Hello,

if you look carefully at help to your block, there is clear info about MODE parameter where is clear 0 -> Read and 1 -> Write procedure. Other modes are available also with specific functions, all is described what MODE you can use with what function.

Hello,
I know about this mode code but that was the question - in order to do a read and write at the same time, it is very important not to lose the communication - I can't just change these parameters from 0 to 1 - I repeat I want to have a permanent active communication both on read and write - should I use 2 server-client block for each PLC ? Of course with other parameters - according to the examples and information in the help.
Or did you use another possibility ? 

Edit: From what I remember on Modbus tcp you can't read and write on the same block at the same time - that's why I couldn't find a code for read and write in the same time.

Thank you for your time. 

Hello,

eeeehm sry, your idea is looks like some missunderstanding and not fully understanding of system and functionality. Modbus is generally half duplex protocol so you can start next transmission/request only after previous finish or error occured. Next idea, you want read and write to Server at same time so you can also understand that 2 different procedures can have conflict at same time, I mean important read and write from right same register logically not expected and dangerous. What data are correct? That readed or writed at that time? Generally communications have own rules what are logical and required to be safe because data are important, correct data.

It's very hard to help if some knowledge is missing. This areas are not easy and therefore some mistakes occures and problems.

Pls describe better what exactly you want to do.

Update: one procedure what i see as correct is at my attachment, I did this picture to better understand what is possible and safe.

Hello,

pls understand one important thing as is in my attachement n.2

This is possible but potentially dangerous as I mentioned in my previous post, depended to your code data share for processing, as example. next important is to understand that this situaion isn't available generally on any Server because next free connection/Port is required at Server side. This is available on PLCs but not generally at standard HW devices acting as Sensors, only if it is clear that it can offer this feature. This is very important to understand.

So if you want still implement this option, your Server need have 2 independed Server blocks with different Port value, logically one for Read and one for Write from Client. What you do then in your code (data share as security mentioned) is up to you. One example can be read some process data like Power, state of HSC or any temperature data. At same time you can write some commands to process control like START/STOP or any other.

Again pls!

All my recomemndations here are with use of read and Write at same time from Client side!