Simatic Holding Register Mapping with DB

Hello Everyone...

I need to some details about the Modbus Mapping with DBs

for example in a project Holding Registers from 40001 to 40523 are mapped to many DBs like
40006 to 40007 are in DB14
40008 to 400010 are in DB17

likewise there are many DBs assigned for holding register 40001 to 400523...i dont know how to find the link between the Holding address and the DBs...and i have no idea how they have mapped the Modbus Holding address to many DBs, were i can find the details of register in the program ?

Please provide some details or any document refer...

Thanks
Macs

Hello Everyone...

I found some details...and still digging the project..

In my case, Holding register 40001 is DB197.DBW0 as per the bitmap, but i want to know how that is assigned/linked, what kind of logic or connection or configuration must be there in the program... and is there a way to find the assignment of Modbus holding register vs DB ?

Thx....

There should be a MODBUS communications block in the program. One of the inputs is for the holding registers (something like (MB_Hold_Reg), which typically points to a DB, often with an array in it. When you send a modbus command to read/write a value in the holding register, it refers to to that DB. THis is true for both Modbus RTU and Modbus TCP.

My guess is that the program in the PLC copies each of the values into the holding register DB before it calls the modbus block, and then it copies them back out afterwards.

Thank you for your support, i tried to find in the program, but no luck.