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Hello,
I am having/expect to have a problem reading historical data from a flow computer. The vendor of the flow computer specifies that historical records can be read using Modbus FC20 but the PLC i am currently working with does not support FC20. As a work-around the vendor says that historical data can be read also using FC3, although only by reading one individual entry at a time. So far so good, the catch is that when doing it using FC3 the two bytes in the modbus message that specify the number of registers requested must have a preset value (index of the historical entry). This will probably cause a problem seeing as my readings will only be 20 words of length for each query but the index will vary. I am expecting the modbus function to return an error code.
I am using a Beckhoff CX2020 PLC (actually not a PLC as it runs Windows CE).
This being said, does anyone know a work around for this issue? Is it a safe bet to assume that the solution will be to resort to low level programming of the serial interface?
Any help or advice is greatly appreciated!
I am having/expect to have a problem reading historical data from a flow computer. The vendor of the flow computer specifies that historical records can be read using Modbus FC20 but the PLC i am currently working with does not support FC20. As a work-around the vendor says that historical data can be read also using FC3, although only by reading one individual entry at a time. So far so good, the catch is that when doing it using FC3 the two bytes in the modbus message that specify the number of registers requested must have a preset value (index of the historical entry). This will probably cause a problem seeing as my readings will only be 20 words of length for each query but the index will vary. I am expecting the modbus function to return an error code.
I am using a Beckhoff CX2020 PLC (actually not a PLC as it runs Windows CE).
This being said, does anyone know a work around for this issue? Is it a safe bet to assume that the solution will be to resort to low level programming of the serial interface?
Any help or advice is greatly appreciated!