A coupler maps sixteen field input states as discrete inputs beginning at protocol address 0. The linked sandbox opens the exact unit, function, address, quantity and value so the reader can verify the PDU rather than copy an unexplained hex string.
Follow the workflow
This Remote-I/O digital-input module example uses Modbus function 02. Select the function from the documented object type and whether the operation is a read or write—not because two register names look similar.
Do this in the product
Open the preconfigured request and confirm the function-code label before running it.
Open the exerciseThe request transmits protocol address 0. Human-facing 0xxxx, 1xxxx, 3xxxx and 4xxxx references are notation, not values to paste blindly into the 16-bit address field.
Do this in the product
Compare the address field with the expected PDU 02 00 00 00 10.
Open the exerciseThe request quantity is 16 and the training value is 0. Multiword data, signed values, enums and decimal scales remain application-map concerns beyond the core Modbus frame.
Do this in the product
Run the server grader and read each function-specific limit check before copying the request.
Open the exerciseA normal Modbus response proves that a server accepted the request format. It does not by itself prove that a motor moved, a valve reached position or a process value is correctly scaled.
Do this in the product
Save the known-good request, then use a paid project to retain later fault and commissioning evidence.
Open the exerciseCore concepts
The simulator creates a repeatable result; these concepts make that result transferable to real vendor software and supervised practical work.
The transmitted address is a zero-based 16-bit field unless the specific device manual states a different table convention.
The expected request begins 02 00 00 00 10; TCP adds MBAP framing while RTU adds unit address, timing and CRC.
Function, address and response can be valid while units, signedness, scale or machine permissions remain wrong.
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Run the foundation exercise publicly, then use a subscription for advanced challenges, saved configurations, full attempt history, sharing, assigned paths and team reporting.
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