Another siemens modbus question

I have a Siemens S7-200 plc I am using port 0 as a modbus port.

The address I am trying to read are "VW*****" in the Siemens program.

I read the help section and they state "V" addresses start the modbus 400000 register.

What i don't get is how this helps me determine the mod bus address for my data I need to read.

Is their a calculator or spread sheet that let's you put in the Siemens address and gives you a equivalent modbus address.

OR can someone give me a little more info on how to cross the addresses over.

THANKS

I am assuming you are setting the Siemens port as the Modbus SLAVE as you make reference to 'reading from the Siemens port'?

What address have you allocated in the MBUS_INIT block? This will determine the registers that will map to the corresponding 40000, 400001 etc

So for example (as per screen shot), the start address is VB2000, so to read 40001.0 (bit level) you would examine V2001.0 in your S7200 code...

Also, i'm sure (and i need to dig out the code i did for this) that you need to do some byte swapping (Siemens side) Hi>Lo etc...

Hope this helps.

Rob