FB_WriteRealOnDelta

The function block enables event-driven writing of a variable of type REAL.

The function block FB_WriteRealOnDelta checks cyclically whether the value at the input fSignal has changed. The cycle time for checking is determined by the parameter tCycleTime. If 0 s is given for tCycleTime, the input signal is examined during every PLC cycle. If the comparison determines that the current value is greater by the value fUpperLimit or less by the value fLowerLimit, the value of the signal is sent to the specified ADS device. The receiver is addressed by means of the AMS-NetId and the port number (see also ADS Device Identification). The position within the receiver is specified by the index group/index offset or by the symbol name. Usually this is the input image or the flags area.

The internal representation of floating point numbers differs according to the hardware being used. While Intel uses the "little endian" format, Motorola uses the "big endian" format. The input variable bSwapLowHighWord can be used to make the necessary adjustment in order to be able to exchange floating point numbers. This is necessary if floating point numbers are to be exchanged between the TwinCAT PLC on a PC and a BC9000, for example.

If the input bEnable is set to FALSE, no further signal transmission is carried out.

Inputs

VAR_INPUT
    bEnable          :  BOOL := FALSE;
    sNetId           :  T_AmsNetId;
    nPort            :  T_AmsPort;
    nIdxGrp          :  UDINT;
    nIdxOffs         :  UDINT;
    sVarName         :  STRING;
    fSignal          :  REAL;
    fLowerLimit      :  REAL;
    fUpperLimit      :  REAL;
    tCycleTime       :  TIME := t#0s;
    bSendNow         :  BOOL;
    bSwapLowHighWord :  BOOL := FALSE;
END_VAR

Name	Type	Description
bEnable	BOOL	Enable function block.
sNetId	T_AmsNetID	AMS NetID of the ADS device to which the value is to be transmitted.
nPort	T_AmsNetID	AMS port number of the ADS device to which the value is to be transmitted.
nIdxGrp	UDINT	Index group within the ADS device into which the value is to be transmitted.
nIdxOffs	UDINT	Index offset within the ADS device into which the value is to be transmitted.
sVarName	STRING	Symbol name within the ADS device into which the value is to be transmitted.
fSignal	REAL	Variable whose value is to be transmitted.
nLowerLimit	REAL	Lower limit value.
nUpperLimit	REAL	Upper limit value.
tCycleTime	TIME	Cycle time in which the input signal is checked to see whether it has exceeded the limit values.
bSendNow	BOOL	The value is transmitted immediately by a positive edge.
bSwapLowHighWord	BOOL	The least significant WORD and the most significant WORD are swapped.

Outputs

VAR_OUTPUT
    bBusy            :  BOOL := FALSE;
    fLastSignal      :  REAL;
    bError           :  BOOL := FALSE;
    nErrorId         :  UDINT := 0;
    nErrorCnt        :  UDINT := 0;
END_VAR

Name	Type	Description
bBusy	BOOL	The transmission is active.
fLastSignal	REAL	Most recently transmitted value.
bError	BOOL	An error occurred during the transmission.
nErrorId	UDINT	ADS error number if an error has occurred.
nErrorCnt	UDINT	Number of failed transmission attempts.

Requirements

Development environment	required TC3 PLC library
TwinCAT v3.0.0	Tc2_DataExchange