Technical data

Basic functions
4.1 Encoder settings
Connection of the SINAMICS S120 to the Technology CPU
94 Product Information, 09/2011, A5E00480378-04
Cyclical actual value: Gn_XIST_1
In the "cyclical actual value" Gn_XIST_1 (n = 1 or 2, number of the encoder), the incremental
change in position of the encoder is transmitted to the PLC. The drive simply evaluates the
counting pulses of the encoder, and generates the "cyclical actual value" from them.
As soon as the drive control unit is connected to the supply voltage, the value zero is always
transmitted via the "cyclical actual value".
The "cyclical actual value" Gn_XIST_1 is always filled by the drive unit, irrespective of
whether an absolute encoder or an incremental encoder is being used.
Note
The data bits of the "cyclical actual value" Gn_XIST_1 (n = 1 or 2, number of the encoder)
must correspond to the structure of the encoder actual value that is configured in
S7T Config. Otherwise, the position information transferred from the encoder to the PLC
will be incorrectly interpreted by the technology CPU.
Absolute actual value: Gn_XIST_2
Non-cyclical encoder values are transmitted in the "absolute actual value" Gn_XIST_2
(n = ...). These values must be requested by the PLC prior to transmission.
The following values may be requested by the PLC via the axis message frame:
● Absolute value of the encoder if an absolute encoder is being used.
● Synchronization position when a synchronization mark (e.g. reference mark) is overshot,
and requested synchronization function (e.g. on-the-fly homing).
● Measurement position when a measuring input on the drive is triggered,
and a measurement function is requested.
The "absolute actual value" is not described with valid values which can then be evaluated in
the PLC until the drive has executed the requested function.