Siemens Sitrans PROBE LU Instruction Manual

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Contents

Remote Operation : PAPage 24 SITRANS Probe LU (PROFIBUS PA) ñ INSTRUCTION MANUAL 7ML19985JB02Cyclic versus Acyclic DataWhen you request data from a device via PROFIBUS PA, there are two possible datatransfer methods. Cyclic data is provided at every bus scan: acyclic data is requested andprovided as needed.Input information is always requested at every bus scan and is set up as cyclic data.Configuration information is only needed periodically and is set up as acyclic data.Cyclic DataWhen you configure SITRANS Probe LU on the PROFIBUS PA bus, there are two slotsavailable for modules.Slot 0 always transmits AIFB1 information1. Slot 1 defaults to Free Place, but can bechanged to AIFB2 information. If you do not wish to have data transmitted, then you mustuse a Free Place module in that slot.Each of the two Analog Input Function Blocks can be set up to return Level, Distance, orVolume. Within the function blocks, the values are scaled according to the userrequirements (please seeAnalog Input Function Blocks 1 and 2 on page 58 for details).AIFB1 and AIFB2 return 5 bytes of data each:The first 4 bytes are the floating point representation (IEEE) of the variable. The variablesare the outputs of the function block. The 5th byte is the status word, and the list ofpossible values is given in the chart below.The 5 bytes must be read consistently, in a contiguous chunk: they cannot be read byte bybyte, and cannot suffer an interrupt. If you are using an S7-300 / 400, you will need to useSFC14 DPRD_DAT: Read Consistent Data of a Standard PD Slave.Note: Each of the slots has to have a module defined in it.1. For more information, please seeAnalog Input Function Blocks 1 and 2 on page 58.Floating Point StatusAIFB2AIFB1 byte 1 byte 2 byte 3 byte 4 byte 5byte 6 byte 7 byte 8 byte 9 byte10byte10