Some modbus devices use 1-based addressing, others use 0-based addressing. When master and slave have different address base, the "shift" occurs. The fastest way to identify this issue is indeed by trial and error, since not all manufacturer state this in the modbus device manual. ... View more

Hello Richard,   You can use READ_VAR and WRITE_VAR functions to communicate to other subnets  through a router/IP forwarding.  If you like to use IO-scanner for this purpose, the BMENOC0301/311 modules support IP addresses on a different subnet. Minimum version of BMENOC firmware should be 2.05 (latest =2.16).     ... View more