CPU313c-2DP and CP341 slave

dilipan_c

hi

we are using CPU313c-2dp and CP341 modbus slave along with dongle

We are going to communicate with DCS. DCS acts as modbus master

DCS needs to read the data from our PLC, DCS uses Function code 3

As per CP341 slave manual, Function code 3 reads the data block DB800 from the PLC

But CPU313c-2dp can have maximum DB number is 511, in that case is it possible to change the DB800

Or what is thesettings we have to do in CPU313c-2dp

regards

dilipan

dilipan_c

hi

we are using CPU313c-2dp and CP341 modbus slave along with dongle

We are going to communicate with DCS. DCS acts as modbus master

DCS needs to read the data from our PLC, DCS uses Function code 3

As per CP341 slave manual, Function code 3 reads the data block DB800 from the PLC

But CPU313c-2dp can have maximum DB number is 511, in that case is it possible to change the DB800

Or what is thesettings we have to do in CPU313c-2dp

regards

dilipan

• Transmission rate, parity

• Slave address of CP

• Operating mode (normal, interference suppression)

• Multiplication factor for character delay time

• Address areas for FC01, 05, 15

• Address areas for FC02

• Base DB number for FC03, 06, 16

• Base DB number for FC04

• Limits for write-only access

Please note the possible selection of the Base DB number for Modbusfunctions 03, 04, 06 and 16. Using these parameters, you do not need to use DB800 as Base DB Number, but anyone that fits your CPU or uyour program.

Hope this hellps,
Daniel Chartier

fritz

Dear dilipan_c

no need to worry, its just a simple matter of misreading the "example" in the CP341 Modbus Slave manual (which is just what the name suggest: An example. Mind you, one could argue that Siemens would create examples that use DB numbers which are supported in all CPU's).

You can use ANY DB as the so called "Base DB" for the Modbus Function codes 3 (Read multiple Registers), 6 (Write single Register) and 16(Write multipleRegisters).
Which DB you want to use as the "Base DB" isdeclared in the Poin to Point parameterisation of the Modbus Slave Driverfor the CP341 and the attached screendump hopefully "saysmore than a thousands words" (DB100 is declared as the Base DB for Modbus FC 3,6&16 in this "example").

I hope this helps

P.S:Apologiesfor the German in the screendumps, my installation is in English but this is not the first time Siemens "forgot" to translate screens.

Fritz is right you use any DB, as long as you declare it on the point to point marameterization. I dont think you would face any issue after doing that.