Danfoss VLT AQUA Drive FC 202 Design Manual

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3.8.10.11 Modbus Exception CodesFor a full explanation of the structure of an exception coderesponse, refer to chapter 3.8.10.5 Function Field.Code Name Meaning1 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 devices,and 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, forexample because it is not configured andis being asked to return register values.2 Illegal dataaddressThe data address received in the query isnot an allowable address for the server(or slave). More specifically, thecombination of reference number andtransfer length is invalid. For a controllerwith 100 registers, a request with offset96 and length 4 would succeed, a requestwith offset 96 and length 5 generatesexception 02.3 Illegal datavalueA value contained in the query data fieldis not an allowable value for server (orslave). This indicates a fault in thestructure of the remainder of a complexrequest, such as that the implied length isincorrect. It specifically does NOT meanthat a data item submitted for storage ina register has a value outside theexpectation of the application program,since the Modbus protocol is unaware ofthe significance of any particular value ofany particular register.4 Slave devicefailureAn unrecoverable error occurred while theserver (or slave) was attempting toperform the requested action.Table 3.42 Modbus Exception Codes3.8.11 Access to Parameters3.8.11.1 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. Example: Reading3-12 Catch up/slow Down Value (16 bit): The holdingregister 3120 holds the parameters value. A value of 1352(Decimal), means that the parameter is set to 12.52%Reading 3-14 Preset Relative Reference (32bit): The holdingregisters 3410 & 3411 holds the parameter’s value. A valueof 11300 (decimal), means that the parameter is set to1113.00.For information on the parameters, size and convertingindex, consult the programming guide.3.8.11.2 Storage of DataThe coil 65 decimal determines whether data written tothe frequency converter is stored in EEPROM and RAM (coil65=1) or only in RAM (coil 65=0).3.8.11.3 IND (Index)Some parameters in the frequency converter are arrayparameters, for example, 3-10 Preset Reference. Since theModbus does not support arrays in the holding registers,the frequency converter has reserved the holding register9 as pointer to the array. Before reading or writing an arrayparameter, set the holding register 9. Setting the holdingregister to the value of 2 causes all following read/write toarray parameters to be to the index 2.3.8.11.4 Text BlocksParameters stored as text strings are accessed in the sameway as the other parameters. The maximum text block sizeis 20 characters. If a read request for a parameter is formore characters than the parameter stores, the response istruncated. If the read request for a parameter is for fewercharacters than the parameter stores, the response is spacefilled.3.8.11.5 Conversion FactorSince a parameter value can only be transferred as a wholenumber, a conversion factor must be used to transferdecimals.3.8.11.6 Parameter ValuesStandard data typesStandard data types are int 16, int 32, uint 8, uint 16 anduint 32. They are stored as 4x registers (40001–4FFFF). Theparameters are read using function 03 hex Read HoldingRegisters. Parameters are written using the function 6 hexPreset Single Register for 1 register (16 bits), and thefunction 10 hex Preset Multiple Registers for 2 registers (32bits). Readable sizes range from 1 register (16 bits) up to10 registers (20 characters).Non-standard data typesNon-standard data types are text strings and are stored as4x registers (40001–4FFFF). The parameters are read usingfunction 03 hex Read Holding Registers and written usingfunction 10 hex Preset Multiple Registers. Readable sizesrange from 1 register (2 characters) up to 10 registers (20characters).System Integration Design GuideMG20N602 Danfoss A/S © 09/2014 All rights reserved. 873 3