Modbus Function Codes Explained (Embedded Developer’s Guide)
This lesson explains Modbus Function Codes from an embedded developer’s perspective.
We break down how function codes define the action a Modbus master requests, how different data types are accessed, and how normal and exception responses are structured.
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In this lesson, we cover:
• What Modbus function codes are and why they matter in master–slave communication
• How the master uses function codes to read or write coils and registers
• Bit-access vs 16-bit register access function groups
• The common function codes every embedded developer should know:
01 Read Coils
02 Read Discrete Inputs
03 Read Holding Registers
04 Read Input Registers
05 Write Single Coil
06 Write Single Register
15 Write Multiple Coils
16 Write Multiple Holding Registers
• How Modbus RTU request frames encode function codes (example: 07 03 00 0D 00 01)
• How normal responses echo the function code and return data
• How exception responses modify the function code (FC + 0x80) and include an error code
This video is part of the Modbus RTU playlist created for embedded developers implementing Modbus on MCUs.
🧩 Modbus RTU Playlist (Embedded Developer Perspective):
• Modbus RTU Explained (From an Embedded Dev...
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