PLC / Industrial Networks & PLC Communications
Check the Modbus function and data table before changing addresses
The same-looking reference number can belong to coils, discrete inputs, input registers or holding registers with different access semantics.
Environment and inputs: Industrial PLC / automation guidance · Verify the exact controller, module, firmware, engineering tool and machine documentation. Linked vendor examples apply to their stated products and library versions; observation, state changes and physical work require distinct authorization.
Observe and record
Compare the exact device's register map, client function selection, data width and approved read or write permissions.
Interpret the evidence
Protocol address fields and human-readable register notation are different conventions. A successful response can still be the wrong table.
Resolve and verify
Correct the configured read mapping using the manufacturer's documented notation and validate a known non-actuating value against the device.
Machine and data safeguards
Do not try write functions on a production device merely to discover which table or address is correct.