Danaher Motion s200 User Manual
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569.4 MODBUS FUNCTIONSTo simplify the communications the S200 Position Node is set up with almost all data defined as32bit values comprised of two 16-bit registers. The data type of any one of these register sets canbe defined as Long, Text, or Float data types. With a few exceptions, all communications to theS200 Position Node card will be Read Holding Registers (FC=03) or Write Multiple Registers (FC= 16).The register address of each parameter is aligned to an even register address values. Variableaddress in the GUI software is set up as 32-bit address space and is called the PDID (usingvariable browser utility). The Modbus registers, being 16 bit address space, are addressed at 2 *PDID value. Please see address table at the end of this chapter.The first register (even address) is the high word of the 32 bit value, the second register (oddaddress) the low word.Important: Although data transfer should be done using FC 16 (Write Multiple Registers,quantity 2) the Position Node does support write of a single register:1. To synchronize the write access when using single register access both registersof a parameter need to be written to starting with the high word (even address). Ifthe low word is accessed first, an error exception occurs.2. The firmware supports only a block read/write access of up to 2 registers. Bothregisters must belong to the same parameter.Each parameter has a set of attributes like minimum value, maximum value, default value, readonly, data type, etc., which can be uploaded from the option card. See tables at the end of thissection for details.9.4.1 Reading VariablesTo read a variable use the Modbus Function ‘Read Holding Registers’. As found in the Modbusdocuments the serial communication model for a variable read is presented as follows:UA=xx FC = 3 Address (16bit) Number of registers (16bit) CRCWhere:UA is the unit address of the drive as set by rotary switches S11 and S12.FC is the Read Multiple Holding Register Function Code (03).Address is the variable register address (even number).Number of registers to read should be set to 2.As defined by Modbus, the S200 Position Node product will respond with the value set in thoseregisters:UA=xx FC=3 data length data CRCWhere:UA is the unit address echoed back.FC is the function code echoed back (03)Data length will be 2 (Data count)Data will be the 32 bit value of the variable read. Variable type may be Long or Float. |
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