Can i connect Delta PLC with Siemens PLC with modbus

[HamzaAhmed]

Hello guys,

I have a siemens PLC and i want to add a new preocess without touch the Siemens code, so i am going to add Delta PLC, this PLC will take values from Siemens PLC via Modbus, is that possible?

in other words: Can i connect Delta PLC with Siemens PLC with modbus?

Thanks,

 

[JesperMP]

What Siemens PLC ?
Modbus RTU or Modbus TCP ?

 

[mk42]

Pretty much regardless of which Siemens PLC it is, they don't have Modbus activated by default, and it isn't typical for them to be using it in most systems.


You'll very likely have to touch the Siemens PLC to add the Modbus instructions, at a minimum. If you want Modbus RTU, you'd need to add the serial module as well.

 

[HamzaAhmed]

What Siemens PLC ?
Modbus RTU or Modbus TCP ?

I want to use Modbus TCP, i can add a special module to the PLC siemens to allow it to communicate with Modbus, no problem with that

 

[HamzaAhmed]

Pretty much regardless of which Siemens PLC it is, they don't have Modbus activated by default, and it isn't typical for them to be using it in most systems.


You'll very likely have to touch the Siemens PLC to add the Modbus instructions, at a minimum. If you want Modbus RTU, you'd need to add the serial module as well.

I can add a special module to the PLC siemens to allow it to communicate with Modbus, no problem with that, but is it possible to write and read from it and the Delta PLC at the same time?

 

[HamzaAhmed]

up

 

[goghie]

Only thing you need to be aware that Siemens does not support Modbus request 23, and that is read and write holding registers at same time, so you need to use separate commands for reading and writing. As usually Siemens had to do some shi**y implementation of Modbus protocol.

 

[HamzaAhmed]

So i have to forget this thing

 

[danw]

i want to add a new preocess without touch the Siemens code,

Modbus is never plug & play.

During Modbus operation, a slave is essentially passive, just doing its Modbus task of fulfilling requests for data or commands to update data from writes to it from the master. But some code is needed to create a set of Modbus registers which defines which data is in which Modbus register. This coding effort violates the "not touching the Siemens code" requirement.

I'm not sure that any comm protocol implementation is hands-off/no-programming because the purpose of communications is to do something with the data being transferred and the task to do something requires some kind of programming.

so i am going to add Delta PLC,
in other words: Can i connect Delta PLC with Siemens PLC with modbus?

Probably, after executing an implementation project, that involves hardware comm connections and some programming on both ends.

 

[Peter Nachtwey]

I would buy a Red Lion Data Station if it supports both protocols and use Ethernet.
https://www.redlion.net/protocol-converters/data-station
Yes, it costs money but in the long run it will be far cheaper.

I hate anything to do with Modbus because of all the support it requires because people think they can roll their own. Those that use Modbus RTU rarely get the timing right because their computers don't have the ability to measure 1.5 or 3.5 character lengths.
Modbus TCP is OK as long as the data is only 16 bits but more projects like motion control require 32bit reals. There is no specification for 32 bit data transfers so often the byte or word order is all screwed up. Since there is no specification for 32 bit transfers we used the ability to communicate 32 bit values with a Modicon/Schneider PLC the standard.
https://modbus.org/docs/MBConformanceTestSpec_v3.0.pdf
Notice there is nothing about 32 bit transfers. This has caused our customers, and us, a lot of problems since the 32 bit values are not transferred correctly so the data must be swapped around in the PLC or motion controller.

On control.com it seems that every 5th post is a question about Modbus RTU or TCP. This is an indicator of poor design or documentation.

 

[goghie]

So i have to forget this thing

No, you don't have to forget it, you need to adapt to the possibilities of hardware. Program the Siemens by adding Modbus slave function and then program the Delta by reading and then writing registers cyclically. Also if you have operator panel, you can use it to do it for you. Connect HMI to Siemens using S7 communication or Profinet, connect HMI to Delta using Modbus and put script inside the HMI that copies data. In that way you will not need to program S7. Most of HMI s have that capability.

 

[HamzaAhmed]

No, you don't have to forget it, you need to adapt to the possibilities of hardware. Program the Siemens by adding Modbus slave function and then program the Delta by reading and then writing registers cyclically. Also if you have operator panel, you can use it to do it for you. Connect HMI to Siemens using S7 communication or Profinet, connect HMI to Delta using Modbus and put script inside the HMI that copies data. In that way you will not need to program S7. Most of HMI s have that capability.

I will try, thank you