What are you using? (e.g., Arduino, PLC, Python script) Are you trying to read data or control a device?
The core instruction containing the Function Code and Data . This is the same across all Modbus versions.
The "envelope" that changes based on the network type. It adds the Address and Error Check . Common Function Codes 01: Read Coils 03: Read Holding Registers 05: Write Single Coil 16 (0x10): Write Multiple Registers ⚠️ Common Pitfalls & Limitations
Some systems use "1-based" numbering (1-65536) in manuals, but the actual protocol uses "0-based" addressing (0-65535). If your data is "off by one," check this first!
Despite its popularity, Modbus has specific quirks that can frustrate newcomers:
Uses a 16-bit Cyclic Redundancy Check (CRC) to ensure data integrity.
General purpose data storage (e.g., setpoints, configurations). Reads external values (e.g., temperature from a sensor). ⚡ Variants of Modbus
