Danfoss VLT HVAC Drive FC 100 Series Design Manual

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Danfoss VLT HVAC Drive FC 100 Series Design Manual Manual pdf 151 page image

7.8.9 How to Control the AdjustableFrequency DriveThis section describes codes which can be used in thefunction and data fields of a Modbus RTU message.7.8.10 Function Codes Supported byModbus RTUModbus RTU supports use of the following function codesin the function field of a message.Function Function CodeRead coils 1 hexRead holding registers 3 hexWrite single coil 5 hexWrite single register 6 hexWrite multiple coils F hexWrite multiple registers 10 hexGet comm. event counter B hexReport slave ID 11 hexTable 7.18Function FunctionCodeSub-functioncodeSub-functionDiagnostics8 1 Restart communication2 Return diagnostic register10 Clear counters anddiagnostic register11 Return bus message count12 Return bus communicationerror count13 Return bus exception errorcount14 Return slave message countTable 7.197.8.11 Modbus Exception CodesFor a full explanation of the structure of an exception coderesponse, please refer to , Function Field.Modbus Exception CodesCodeName MeaningModbus Exception Codes1 IllegalfunctionThe function code received in the query isnot an allowable action for the server (orslave). This may be because the functioncode is only applicable to newer devicesand was not implemented in the unitselected. It could also indicate that theserver (or slave) is in the wrong state toprocess a request of this type, for examplebecause it is not configured and is beingasked to return register values.2 Illegal dataaddressThe data address received in the query isnot an allowable address for the server (orslave). More specifically, the combination ofreference number and transfer length isinvalid. For a controller with 100 registers, arequest with offset 96 and length 4 wouldsucceed, a request with offset 96 and length5 will generate exception 02.3 Illegal datavalueA value contained in the query data field isnot an allowable value for server (or slave).This indicates a fault in the structure of theremainder of a complex request, such asthat the implied length is incorrect. It specif-ically does NOT mean that a data itemsubmitted for storage in a register has avalue outside the expectation of theapplication program, since the Modbusprotocol is unaware of the significance ofany particular value of any particularregister.4 Slave devicefailureAn unrecoverable error occurred while theserver (or slave) was attempting to performthe requested action.Table 7.207.9 How to Access Parameters7.9.1 Parameter HandlingThe PNU (Parameter Number) is translated from theregister address contained in the Modbus read or writemessage. The parameter number is translated to Modbusas (10 x parameter number) DECIMAL.7.9.2 Storage of DataThe Coil 65 decimal determines whether data written tothe Adjustable frequency drive are stored in EEPROM andRAM (coil 65 = 1) or only in RAM (coil 65 = 0).RS-485 Installation and Set... VLT® HVAC Drive Design GuideMG11BB22 - VLT® is a registered Danfoss trademark 7-157 7