Danfoss VLT AQUA Drive FC 202 Design Manual

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Contents

7.9 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 (10xparameter number) DECIMAL.7.9.2 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).7.9.3 INDThe array index is set in holding register 9 and used whenaccessing array parameters.7.9.4 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.7.9.5 Conversion FactorThe different attributes for each parameter can be seen inthe section on factory settings. Since a parameter valuecan only be transferred as a whole number, a conversionfactor must be used to transfer decimals.7.9.6 Parameter ValuesStandard data typesStandard data types are int16, int32, uint8, uint16, anduint32. They are stored as 4x registers (40001–4FFFF). Theparameters are read using function 03 HEX "Read HoldingRegisters." Parameters are written using the function 6 HEX"Preset Single Register" for 1 register (16-bits), and thefunction 10 HEX "Preset Multiple Registers" for 2 registers(32-bits). Readable sizes range from 1 register (16 bits) upto 10 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 writtenusing function 10 HEX "Preset Multiple Registers." Readablesizes range from 1 register (2 characters) up to 10 registers(20 characters).7.10 Examples7.10.1 Read Coil Status (01 HEX)DescriptionThis function reads the ON/OFF status of discrete outputs(coils) in the frequency converter. Broadcast is neversupported for reads.QueryThe query message specifies the starting coil and quantityof coils to read. Coil addresses start at zero.Example of a request to read coils 33–48 (Status Word)from slave device 01.Field Name Example (HEX)Slave Address 01 (frequency converter address)Function 01 (read coils)Starting Address HI 00Starting Address LO 20 (32 decimals) Coil 33No. of Points HI 00No. of Points LO 10 (16 decimals)Error Check (CRC) -Table 7.19 QueryResponseThe coil status in the response message is packed as onecoil per bit of the data field. Status is indicated as: 1 = ON;0 = OFF. The LSB of the first data byte contains the coiladdressed in the query. The other coils follow toward thehigh-order end of this byte, and from ‘low order to highorder’ in subsequent bytes.If the returned coil quantity is not a multiple of eight, theremaining bits in the final data byte are padded with zeros(toward the high-order end of the byte). The Byte Countfield specifies the number of complete bytes of data.Field Name Example (HEX)Slave Address 01 (frequency converter address)Function 01 (read coils)Byte Count 02 (2 bytes of data)Data (Coils 40–33) 07Data (Coils 48–41) 06 (STW=0607hex)Error Check (CRC) -Table 7.20 ResponseNOTICECoils and registers are addressed explicit with an off-setof -1 in Modbus.Coil 33 is addressed as Coil 32, for example.RS-485 Installation and Set... Design Guide160 Danfoss A/S © Rev. 06/2014 All rights reserved. MG20Z20277