6-1
IM 178-4
C79000-G7076-C178-01
Functions of the IM 178-4
6.1
Description of the Functions
6.1.1
Cyclic Processing
The user data area of the outputs is evaluated and the user data area of the inputs
is updated cyclically (for the update rate, refer to Section A.1).
Detecting the Actual Position Value with Absolute Position Encoders
When using absolute position encoders (13, 21 or 25 bit frame), then depending on
the parameter assignment, the sensor signals are sent and normalized via a
selectable serial Gray/binary converter. By using the normalization function, you
can shift out a selectable number of bits following the sensor values. Some
sensors provide additional information in these subsequent bits, such as power
error or to indicate that a limit value has been reached. If the absolute position
encoder you are using supplies less bits than the selected frame contains, the
following bits must either be masked out in your program or shifted out by
normalization.
Gray code sensors whose frame does not begin with the MSB can only be used
when all the preceding bits (special bits such as power error) always have the
value 0.
The IM 178-4 enters the actual position value as a 32-bit value in the user data
area of the inputs. If an SSI frame error occurs, the last correct actual position
value is retained.
The Synchronization parameter is not evaluated.
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