SimpleReadValue

SimpleReadValue (FB)

FUNCTION_BLOCK SimpleReadValue

Short description

Used to read a Modbus value of different function codes as well as different data types up to 64-bit values. Addresses to be read are automatically expanded to up to 4 registers for values larger than 16 bits. Via an array the raw values can always be processed directly. As a parameter there is the option to scale values directly.

Representation

Evaluation of the actual values for function codes 01 (Read Coils) and 02 (Read Discrete Inputs)

When evaluating the actual values, only the output 'arwRawValue' should be considered. It is an array consisting of four variables 'arwRawValue[0]' - 'arwRawValue[3]' of type WORD ( = 16 bit ). The determination of the bits to be transmitted is primarily made by the choice of the function code ( eFunctionCode ) and the start address ( wRegisterAddr ). The number of bits to be transmitted is defined by the choice of the expected data type ( eExpectedType ). Depending on the data type, therefore, 16, 32 or 64 consecutive bits are transmitted. At least 16 consecutive bits are always transmitted. The actual values are available as follows: 16 transmitted bits: actual values in 'arwRawValue[0]' 32 transmitted bits: actual values in 'arwRawValue[0]' and 'arwRawValue[1]' 64 transmitted bits: actual values in 'arwRawValue[0]', 'arwRawValue[1]', 'arwRawValue[2]' and 'arwRawValue[3]' Task: Read the actual value of coil 17 Settings: eFunctionCode: ReadFunctionCodes.FC01_ReadCoils wRegisterAddr = 17 eExpectedType = EXPECTED_TYPE.TYPE_BYTE ( = 8 bit ) Due to the fact that at least 16 consecutive bits are always transmitted, the actual values of coils 17 - 32 are requested. After successful transmission the actual values are available in the variable 'arwRawValue[0]': 'arwRawValue[0].0': actual value of coil 17 'arwRawValue[0].1': actual value of coil 18 'arwRawValue[0].2': actual value of coil 19 'arwRawValue[0].3': actual value of coil 20 'arwRawValue[0].4': actual value of coil 21 'arwRawValue[0].5': actual value of coil 22 'arwRawValue[0].6': actual value of coil 23 'arwRawValue[0].7': actual value of coil 24 'arwRawValue[0].8': actual value of coil 25 'arwRawValue[0].9': actual value of coil 26 'arwRawValue[0].10': actual value of coil 27 'arwRawValue[0].11': actual value of coil 28 'arwRawValue[0].12': actual value of coil 29 'arwRawValue[0].13': actual value of coil 30 'arwRawValue[0].14': actual value of coil 31 'arwRawValue[0].15': actual value of coil 32\

CODESYS

InOut:

Scope	Name	Type	Initial	Comment
Input	xEn	BOOL	TRUE	Enable / disable of communication ( TRUE = enabled )
Input	byUnitId	BYTE	0	Address of the device
Input	xUpdateActual	BOOL	FALSE	Update of actual values ( on each rising edge )
Input	xResError	BOOL	FALSE	Reinitialization of the outputs 'eErrorCodeCom' and/or 'eErrorCodeDev' to the no-error state (on every rising edge)
Inout	ModbusClient	ModbusClientBase		Client of the device
Output	eExpectedTypeFb	EXPECTED_TYPE		Feedback - expected data type for the received Modbus data
Output	eFunctionCodeFb	ReadFunctionCodes		Feedback - Modbus function code for the Modbus telegram
Output	wRegisterAddrFb	WORD		Feedback - start address of the register for the Modbus telegram
Output	arwRawValue	ARRAY [0..3] OF WORD		Raw values of the registers of the Modbus telegram
Output	rScaleFactorFb	REAL		Feedback - scaling factor — formula: rValue = rawVal * rScaleFactor
Output	xBigEndianFb	BOOL		Feedback - position of the most significant element in a datum ( TRUE = lowest memory location )
Output	xSwapValueFb	BOOL		Feedback - enable/disable of the byte position swap of a register ( TRUE = swap active )
Output	rValue	REAL		Final value ( formula: rValue = rawVal * rScaleFactor ), parameters: eExpectedType, xSwapValue, xIsBigEndian and rScaleFactor
Output	xAlarm	BOOL		Collective fault ( TRUE = fault )
Output	xAlarmCom	BOOL		Collective fault - communication ( TRUE = fault )
Output	eErrorCodeCom	ModbusErrorCode		Error code - communication ( 0 = no error )
Output	eErrorCodeDev	SIMPLE_READ_VALUE_ERROR_CODE		Error code - device (0 = no error)
Output	xBusy	BOOL		Communication indicator ( TRUE = communication )
Input Const	xBigEndian	BOOL	FALSE	Position of the most significant 16 bits in a datum ( TRUE = most significant 16 bits first ) ( only relevant for 32 / 64 bit )
Input Const	xSwapValue	BOOL	TRUE	Enable/disable of the byte position swap of a register ( TRUE = swap active ) ( only relevant for 32 / 64 bit )
Input Const	rScaleFactor	REAL	1.0	Scaling factor — formula: rValue = rawVal * rScaleFactor
Input Const	eExpectedType	EXPECTED_TYPE	EXPECTED_TYPE.TYPE_UINT16	Expected data type for the received Modbus data
Input Const	eFunctionCode	ReadFunctionCodes	ReadFunctionCodes.FC03_ReadHoldingRegisters	Modbus function code for the Modbus telegram
Input Const	wRegisterAddr	WORD		Start address of the register for the Modbus telegram
Input Const	tTimeUpdateActual	TIME	TIME#3s0ms	Update interval for the processes affected by the input ‘xUpdateActual’