You need to set up the slave device (Modbus Slave ID Number is always relevant) first in whatever software is used (see page 6 of document from B+B), then switch to the S7 master and give it a go.
First , thanks for the help.
I assume the IDEC software is free somewhere and you propose to work around Siemens just to change the slave address. While this gets the job done, it sort of lets Siemens off the hook.
A part of me realy wants to force them to face thier own documentation and software with me. I am beyond just trying to work something out. I want someone at Siemens to receive my feedback and possibly add it to others and actualy bring a better product to us or at least a revised manual.
The Siemens software should be able to change the slave address.
If not, it needs to be fixed so it can.
And the documentation needs to be more concise and more clear.
Hopefully, after I get to a good point , I can organize everything I have been through with this S7 adventure into a tutorial or maybe even a book.
A book , unlike Hern Berger's book and the Siemens docs, that is easy to follow.
Today a Siemens rep tells me I need the dongle and a license to use the CP341 to communicate as a Modbus slave.
Then he says, "I do not believe the RS232 CP 341 alone will communicate Modbus"
Not sure what he means by this.
I am still digging and will return here for suggestions and to update if I find more information.
Thanks again.