Best way to poll for Modbus RTU slaves through a Modbus TCP gateway
There are no guaranteed addresses or registers with ModBus; that's one of its biggest failings (or one if it's greatest strengths, depending on how (in)experienced you are in the field). There have been numerous attempts to generate some kind of standard for common devices but ultimately there is no way to do this since there is no standards body oversight for such a thing to succeed.