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PROFIBUS AND MODBUS

Thread Starter: Gourav   Started: 12/3/2010 8:35 AM   Replies: 7

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  12/3/2010, 8:35 AM
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HELLO,

whats the difference between Profibus and Modbus ?

Are the hardware topology for both the protocols same ?

what to do with the software (SIMATIC Manager) for communicating on MODBUS ?

I know that I have to connect extra modbus module for it. Can anyone give me some idea about MODBUS ?
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  12/3/2010, 10:00 AM
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Gourav wrote:
HELLO,

whats the difference between Profibus and Modbus ?

Are the hardware topology for both the protocols same ?

what to do with the software (SIMATIC Manager) for communicating on MODBUS ?

I know that I have to connect extra modbus module for it. Can anyone give me some idea about MODBUS ?


Hi Gourav,

Have a Look on the Modbus Link,

If you want to used the Modbus then you have to used the CP341 for S7-300 Series PLC,

SIMATIC S7-300/S7-400 Loadable Driver for Point-to-Point CPs: MODBUS protocol, RTU format, S7 is master

SIMATIC S7-300/S7-400 Loadable Driver for Point-to-Point CPs: MODBUS Protocol, RTU format, S7 is Slave

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Ammy

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  12/3/2010, 11:20 AM
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Dear Gourav,

just to add one point. If you have MODBUS as Network STEP 7 has no direct access to it. The only thing you can do is to configure the MODUBUS interface (CP 341) and program the Master or Slave function used with this CP.

Just as an add on information.

Best regards
J_Bell
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  12/5/2010, 9:14 PM
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Dear Gourav,

Also a CP441-2 may be used for MODBUS RTU, an ET 200S SI-module can also be used for MODBUS.

Physically both networks have a master and slaves, they use both RS 485 as layer. PROFIBUS is much faster then MODBUS, there are 1000's of slaves for PROFIBUS. The PNO have also now PROFINET, that is on ethernet base and working fast on layer 2.

I hope that the answer will help, if you have still questions, don't hesitate to ask me.

All the best, Late
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  12/6/2010, 8:32 AM
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hello,

I am working on ET200S modules.
I have a modbus module to communicate on modbus.
 
Now I want to know that as we connect the profibus to profibus connector. Is it same for the modbus ?
If its different than how ?
Also profibus communicates in ring topology. So even modbus do the same ?
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  12/6/2010, 12:34 PM
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Gourav wrote:

Now I want to know that as we connect the profibus to profibus connector.
Is it same for the modbus ?

Essentially yes if you are using RS485. Profibus is just another protocol that is sent over RS485.
So electrically they are the same. So the connections are the same.
I have even used profibus cable for modbus comms in the past with no issues.

Gourav wrote:

Also profibus communicates in ring topology. So even modbus do the same ?

It is feasable for modbus RS485 to work in ring topology, but it is not recomended (as is star topology as well).
The recomended topology for modbus RS485 is bus.
The two most extreme nodes on the network (physically) should have line terminators fitted (120 Ohm).

Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots.

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  12/7/2010, 7:23 AM
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THANKS.

I THINK THIS WILL HELP ME A LOT

ALSO IN SIMATIC MANAGER WHILE ADDING THE MODULE, WILL I HAVE TO INSTALL THE GSD FILE FOR THE MODBUS MODULE ?
IF YES THEN FROM WHERE CAN I GET THE GSD FILES ?




=== Edited by Gourav @ 12/7/2010 7:26 AM [GMT ] ===


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  12/7/2010, 4:00 PM
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Hello Gourav;
Please download and have a good look at the manuals proposed earlier by Ammy.
You will see that there are no gsd files used in Modbus communications.


When you setup a Profibus-DP link, you configure data from each slave through its gsd fiile, and then determine its data exchange caracteristics (address and amount of data exchanged between master and slave) once, before launching communications. Each profibus slave is then polled cyclically by the master, based on the determined configuration.

In Modbus, you have to program (or configure) the Modbus Function required for each spoecific exchange between master and slave, specifically the slave address, the location of data in the slave and the amount of registers exchanged, for every Modbus job. In the Siemens communication functions for Modbus, you define these parameters in the DataBlocks you must develop for every Modbus Function request.

Please study these in the recommended manuals, and the program examples in the Modbus Master document, so you have a clear idea of what you need to establish Modbus comms on a Siemens CPU. Then come back to the forum with more detailed questions, we will try to help.

Hope this helps,
Daniel Chartier



=== Edited by dchartier @ 12/7/2010 4:05 PM [GMT ] ===


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