Modbus Function Codes
Each command starts with an address followed by a function code. These are used to read data from discrete inputs and input registers. They can also read/write data on coils and holding registers of each Modbus device you address.
The following is a table of object types provided by a Modbus slave device to a Modbus master device:
The frame format is composed of an Application Data Unit (ADU), which encloses a Protocol Data Unit (PDU):
Most used Function Codes
All Modbus Function Codes
The various reading, writing and other operations are categorised as follows. The most primitive reads and writes are shown in bold. A number of sources use alternative terminology, for example Force Single Coil where the standard uses Write Single Coil. Prominent entities within a Modbus slave are:
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