FB_WriteRealOnDelta

Event-driven writing of a variable of type REAL.

The FB_WriteRealOnDelta() function block checks cyclically whether the value at the fSignal input has changed. The cycle time within which the check is carried out is specified by the parameter tCycleTime. If 0 seconds is given for tCycleTime, the input signal is examined during every PLC cycle. If the comparison establishes that the current value is greater than fUpperLimit or lower than the value fLowerLimit, then the value is sent to the ADS device that is to be specified. 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. Whereas Intel use the "little-endian" format, Motorola-based hardware employs the "big-endian" format. The input variable bSwapLowHighWord can be used to make the necessary adjustment to be able to exchange floating point numbers. This is necessary, for instance, if floating point numbers need to be exchanged between the TwinCAT PLC running on a PC and a BC9000.

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

bEnable          : BOOL := FALSE;
sNetId           : T_AmsNetId;
nPort            : T_AmsPort := AMSPORT_R0_PLC_RTS1;
nIdxGrp          : UDINT;
nIdxOffs         : UDINT;
sVarName         : STRING;
fSignal          : REAL;
fLowerLimit      : REAL;
fUpperLimit      : REAL;
tCycleTime       : TIME := t#0s;
bSendNow         : BOOL;
bSwapLowHighWord : BOOL := FALSE;

bBusy          : BOOL;
fLastSignal    : BYTE;
bError         : BOOL;
nErrorId       : UDINT;
nErrorCnt      : UDINT;