Communicating with the PLC
6.2 MODBUS communication
SINAMICS V20 Inverter
Operating Instructions, 07/2012, A5E03728167
115
Control data
● HSW (Haupsollwert): speed setpoint
● HIW (Hauptistwert): actual speed
● STW (Steuerwort): control word
● ZSW (Zustandswort): status word
For more information, see parameters r2018 and P2019 in Chapter "
Parameter list
(Page
117)".
Parameter scaling
Due to the limits of the integer data in the MODBUS protocol, it is necessary to convert the
inverter parameters before transmitting them. This is done by scaling, so that a parameter,
which has a position after decimal point, is multiplied by a factor, to get rid of the fractional
part. The scaling factor is as defined in the above table.
BICO parameters
The updating of BICO parameters will also be done in the parameter processing in the
background. Because of the limitations of the register value, it is only possible to write a ‘0’
or a ‘1’ to a BICO parameter. This will set BICO input to a static value of either ‘0’ or ‘1’. The
previous connection to another parameter is lost. Reading the BICO parameter will return the
current value of the BICO output.
For example: MODBUS register number 40200. Writing a value 0 or 1 to that register will set
the BICO input P0731 statically to that value. Reading will return the BICO output, which is
stored in r0747.0.
Fault
A fault (F72) should be triggered if:
● The parameter P2014 (USS / MODBUS telegram off time) is not equal to 0
AND
● Process data has been received from the master since the inverter's start-up
AND
● The time between receipts of two consecutive process data telegrams exceeds the value
of P2014.
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