General Modbus slave functions. More...

Data Structures
struct	modbusSlaveUserFunction
	Associates user defined parser function with the function ID. More...

struct	modbusSlave
	Represents Modbus slave device's status and configuration. More...

Typedefs
typedef struct modbusSlaveUserFunction	ModbusSlaveUserFunction
	Associates user defined parser function with the function ID. More...

typedef enum modbusRegisterQuery	ModbusRegisterQuery
	Represents register callback function. More...

typedef uint16_t(*	ModbusRegisterCallbackFunction) (ModbusRegisterQuery query, ModbusDataType datatype, uint16_t index, uint16_t value, void *ctx)
	Type representing a pointer to the user-defined register callback function. More...

typedef struct modbusSlave	ModbusSlave
	Represents Modbus slave device's status and configuration. More...

Enumerations
enum	modbusRegisterQuery { MODBUS_REGQ_R, MODBUS_REGQ_W, MODBUS_REGQ_R_CHECK, MODBUS_REGQ_W_CHECK }
	Represents register callback function. More...

Functions
ModbusError	modbusBuildException (ModbusSlave *status, uint8_t function, ModbusExceptionCode code)
	Builds an exception frame and stores it in the ModbusSlave structure. More...

ModbusError	modbusParseRequest (ModbusSlave *status)
	Interprets incoming Modbus request frame located in the slave structure. More...

ModbusError	modbusSlaveInit (ModbusSlave *status)
	Performs initialization of the ModbusSlave structure. More...

ModbusError	modbusSlaveEnd (ModbusSlave *status)
	Frees memory used by slave structure, previously initialized with modbusSlaveInit. More...

static ModbusError	modbusBuildExceptionErr (ModbusSlave *status, uint8_t function, ModbusExceptionCode code, ModbusFrameError parseError)
	Handles Modbus parsing errors. More...

Detailed Description

General Modbus slave functions.

Note: This header file is suitable for C++

Typedef Documentation

◆ ModbusRegisterCallbackFunction

typedef uint16_t( * ModbusRegisterCallbackFunction) (ModbusRegisterQuery query, ModbusDataType datatype, uint16_t index, uint16_t value, void *ctx)

Type representing a pointer to the user-defined register callback function.

See also: User-defined Modbus register callback function

Parameters

query	A register query (see ModbusRegisterQuery)
datatype	Modbus data type
index	Address of the register
value	Value of the register (only used with write access queries)
ctx	User's context data (passed from ModbusSlave::registerCallbackContext)

◆ ModbusRegisterQuery

typedef enum modbusRegisterQuery ModbusRegisterQuery

Represents register callback function.

Note: Requires REGISTER_CALLBACK or COIL_CALLBACK module (see Building liblightmodbus)

See also: User-defined Modbus register callback function

◆ ModbusSlave

typedef struct modbusSlave ModbusSlave

Represents Modbus slave device's status and configuration.

◆ ModbusSlaveUserFunction

typedef struct modbusSlaveUserFunction ModbusSlaveUserFunction

Associates user defined parser function with the function ID.

Note: Requires SLAVE_USER_FUNCTIONS module (see Building liblightmodbus)

See also: user-functions

Enumeration Type Documentation

◆ modbusRegisterQuery

enum modbusRegisterQuery

Represents register callback function.

Note: Requires REGISTER_CALLBACK or COIL_CALLBACK module (see Building liblightmodbus)

See also: User-defined Modbus register callback function

Enumerator
MODBUS_REGQ_R	Requests callback function to return register value.
MODBUS_REGQ_W	Requests callback function to write the register.
MODBUS_REGQ_R_CHECK	Asks callback function if register can be read.
MODBUS_REGQ_W_CHECK	Asks callback function if register can be written.

Function Documentation

◆ modbusBuildException()

ModbusError modbusBuildException	(	ModbusSlave *	status,
		uint8_t	function,
		ModbusExceptionCode	code
	)

Builds an exception frame and stores it in the ModbusSlave structure.

The exception frame is only built if the request was not broadcasted.

Updates ModbusSlave::lastException member in provided ModbusSlave structure.

This function is used by more sophisticated modbusBuildExceptionErr().

Parameters

status	The slave structure to work on
function	Function code of function throwing the exception
code	A Modbus exception code

Returns: A ModbusError error code. Unlike other library functions, this one returns MODBUS_ERROR_EXCEPTION on success as a form of information that exception had been thrown. If the request was broadcasted, returns MODBUS_ERROR_OK

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◆ modbusBuildExceptionErr()

static ModbusError modbusBuildExceptionErr	(	ModbusSlave *	status,
		uint8_t	function,
		ModbusExceptionCode	code,
		ModbusFrameError	parseError
	)

inlinestatic

Handles Modbus parsing errors.

This function causes an exception frame to be built by modbusBuildException, but additionally stores the more verbose error code in the provided slave structure. This routine should be used for handling parsing errors, whilst the modbusBuildException() should be used for building exception frames with no side effects.

Parameters

status	The slave structure to work on
function	Function code of the function throwing the exception
code	Exception code to be thrown
parseError	More specific error code

Returns: An ModbusError error code. Unlike most library functions, this one returns MODBUS_ERROR_PARSE (when exception frame is not supposed to be built) or MODBUS_ERROR_EXCEPTION (when exception frame has been successfully built) on success. This is because, these are the values that shall be returned by a parsing function upon facing parsing problem.

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◆ modbusParseRequest()

ModbusError modbusParseRequest ( ModbusSlave * status )

Interprets incoming Modbus request frame located in the slave structure.

Firstly, the function frees memory allocated for the previous response frame (ModbusSlave::response) (if dynamic memory allocation is enabled). Then, integrity of the frame is verified with modbusCRC function.

If the frame CRC is correct, the destination slave address is checked. Frames meant for other slave devices are discarded at this point.

Before attempting to parse the frame with one of the built-in parsing functions, the array of user-defined parsing functions is searched. It is important to mention that functions defined by user override the default ones. That is to say, a NULL pointer in the function array can disable support of specific function.

If matching function is found, it is exected and modbusParseRequest() returns the same error code the parsing function code had returned. Otherwise, an exception informing the master device of illegal function code is constructed, and MODBUS_ERROR_EXCEPTION is returned.

Parameters

status The slave structure to work on

Returns: A ModbusError error code.

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◆ modbusSlaveEnd()

ModbusError modbusSlaveEnd ( ModbusSlave * status )

Frees memory used by slave structure, previously initialized with modbusSlaveInit.

Parameters

status The slave structure to work on

Returns: A ModbusError error code

◆ modbusSlaveInit()

ModbusError modbusSlaveInit ( ModbusSlave * status )

Performs initialization of the ModbusSlave structure.

Parameters

status The slave structure to be initialized

Returns: A ModbusError error code.

Data Structures

Typedefs

Enumerations

Functions

Detailed Description

Typedef Documentation

◆ ModbusRegisterCallbackFunction

◆ ModbusRegisterQuery

◆ ModbusSlave

◆ ModbusSlaveUserFunction

Enumeration Type Documentation

◆ modbusRegisterQuery

Function Documentation

◆ modbusBuildException()

◆ modbusBuildExceptionErr()

◆ modbusParseRequest()

◆ modbusSlaveEnd()

◆ modbusSlaveInit()