5/18/2014 3:17 PM | |
Joined: 11/21/2007 Last visit: 8/12/2024 Posts: 2325 Rating:
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Hello Titas Yes you can !! Basically you need to use the ASCII Communication mode of the PtP port and add your own CRC Evaluation logic in the STEP7 program. Besides you need to format the Modbus Send / Receive packets on your own. There is no standard Modbus library available from Siemens for PtP ports. We use PtP routinelyto communicate with Energy Analysers on RS485 using Modbus RTU Protocol. These have been in operation for a long time without any issues. If you google, you will find a few third party libraries for Modbus Communication using PtP port. I cannot vouch for their quality as I have never tried them. Hope this helps Cheers Navnag |
There is no such thing as the last bug in a program |
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5/19/2014 2:01 PM | |
Joined: 11/21/2007 Last visit: 8/12/2024 Posts: 2325 Rating:
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Thanks smiffyfor sharing your experience. We have actually followed a different way of implementation. We had prepared a few building blocks and we combine them to create standard Modbus communication blocks for various type of devices . e.g. by now we have a library of Functions for most of the Modbus devices with which we regularly communicate e.g. Energy Meters / Energy analysers of various manufacturers including SIEMENS PAC 3100 / SIMEAS-P50 , Temprature Scanners, Electro Static Precipitators, PID Controllers, Non Siemens Drives etc. ) These are module blocks which need to be called once per device with the Device ID. The Block reads all the required parameters from the device andtransfers them to a DB / UDT after preprocessing / scaling etc. Thick allows us tokeep the code size to a minimum andallowes us to easily re-use the block when same device is used in another project /PLC. Even Junior programmers can easily use them in their projects. The blocks are independent ofthe CP ( We can use CP 340, CP 341, PTP Port, ET200S 1SIASCII / 1SI Modbus ) . In case of 1SI Modbus, we de-activate the CRC in program as same is handled by the module. Currently our blocks do not support TCP, but we are in the process of updating them. In factI believe that Siemens Modbus Master Driver for CP341 is a complete waste of money asit hardly provides any functionality ( Except perhaps CRC checking ). On the other hand the MODBUS TCP/IP library provides good functionality. I am sharing this, so that other users can adopt the method most suited to their specific needs. Hope this helps Cheers Navnag |
Last edited by: Navnag at: 5/19/2014 2:03 PMThere is no such thing as the last bug in a program |
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