Register notation is not the wire address
A manual may label a holding register 40001, but the Modbus application data unit normally carries address 0. Confirm whether a vendor table is one-based or zero-based before blaming the network.
Protocol workbench
Modbus Simulator
Run real Modbus request exercises before you connect a PLC, drive or meter.
Run before signup Server-graded Save, share and fork
Open the workbench industrial-lab / modbus
MODETRAINING
GRADERSERVER AUTHORITY
EVIDENCECHECKS + SCORE
First challenge
Read two holding registers
Poll unit 1 for the first two holding registers using the protocol data address.
Real Modbus simulator footage
See this exact skill in the working simulator.
Watch the real browser product respond to the task on this page, then try the same practical workflow yourself. No slides, concept mockups, install, or credit card.
Try this in the browserRead the request from wire to application
Prove the Modbus map before blaming the network.
Modbus troubleshooting becomes predictable when you separate transport, unit identity, function, protocol address, data representation and application behavior. These views follow the same sequence used in the interactive workbench.
Interactive request lab
Configure. Run. Read the evidence.
Foundation
Read two holding registers
Poll unit 1 for the first two holding registers using the protocol data address.
Evidence appears here
The backend calculates the expected result and returns individual checks, a score and reproducible evidence. Client-supplied scores are ignored.
Your run is free. Keep the evidence when it matters.
Create an account only when you want saved attempts, projects, sharing and progress.
Training outcomes
More than a calculator.
Each run teaches a transferable industrial workflow and produces evidence you can inspect, repeat and discuss.
01
Translate 4xxxx register notation into the zero-based address carried on the wire.
02
Choose function 03, 06 and exception responses without vendor-specific software.
03
Save a register-map fixture, share it with a class and fork a colleague’s setup.
04
Build evidence from graded attempts instead of relying on a self-marked worksheet.
Field method
How to reason through the lab
Start with one known-good request
Prove the unit ID, function, address and quantity with the smallest possible poll. Expand the block only after the device returns a normal response.
Read the exception byte
An exception response is useful evidence. Function 83 with code 02 means the device understood a function-03 request but the requested address range was not mapped.
Continue from a single exercise to a complete training record.
Guided scenarios, saved progress, fault diagnosis and instructor reporting are built into the main platform.
Technical practice library
Load a real job, not an empty calculator.
Each reference explains a distinct industrial task and links back to an exact grader preset with server-owned acceptance evidence.
Variable-frequency drive
Read VFD Output Frequency With Modbus Function 03
Compose a Modbus request for a VFD output-frequency holding register and verify the zero-based address and quantity.
Energy meter
Read an Energy Meter With Modbus Function 04
Build a two-register input-register poll for a 32-bit energy-meter value and retain word-order evidence.
Panel temperature controller
Read a Temperature Controller Process Value Over Modbus
Compose a function-03 poll for a scaled temperature process value at protocol address 200.
Remote-I/O coupler
Read 16 Remote-I/O Coils With Modbus Function 01
Build a packed 16-coil function-01 poll and verify the bit quantity and zero-based start address.
Remote-I/O digital-input module
Read 16 Remote-I/O Inputs With Modbus Function 02
Compose a Modbus function-02 request for 16 read-only remote-I/O inputs and verify the address, quantity and packed-bit evidence.
Pump controller
Write a Pump Run Coil With Modbus Function 05
Encode an ON command as FF00 for a documented pump run coil and verify the function-05 request.
Temperature controller
Write a Temperature Setpoint With Modbus Function 06
Compose a single-register setpoint write and preserve the distinction between engineering units and the scaled register value.
Alarm annunciator
Write an Alarm Reset Block With Modbus Function 15
Build a packed eight-coil function-15 write and check quantity, byte count and ownership boundaries.
Technical review
Primary references used for this lab
Reviewed 7 August 2026. The simulator teaches a repeatable training method; always use the exact module and instrument manuals for live commissioning work.
Modbus Simulator questions
What learners and instructors ask.
The exercises teach the shared Modbus application protocol used by both. The request grader covers unit IDs, function codes, data addresses, quantities, values and exceptions; the tutorials explain TCP transaction framing and RTU serial timing separately.