Shared application model, different transport
Modbus is an application protocol for exchanging device data through requests and responses. RTU uses serial-line framing; TCP transports messages over TCP/IP. Wiring or network settings do not explain the meaning of individual data fields. Determine function codes, address mapping, read/write permission and update intervals from the documentation for the actual device and firmware.
Example: numeric response, incorrect weight
If an example device returns 12345 and its documented scale is 0.01 kg, the interpreted result is 123.45 kg. Displaying the raw number as kilograms may pass a connectivity test while corrupting operational records. That scale is illustrative. For multi-register values, verify word order, signed/unsigned interpretation and address numbering against the manufacturer’s map and known test values.
Failure handling and access control
Define timeouts, retry counts, invalid responses and how long a previous value remains usable. Repeating a write must not inadvertently trigger an operation twice. A standard Modbus endpoint should not be exposed directly to the internet; design network separation and authorised access. Modbus Security is a separate specification and cannot be assumed to be supported by every Modbus device.