1.0 Encoder Classification
Two device classes are defined in this profile, one Mandatory class (class 1) and
one class with Optional functions (class 2).
1.1 Device class 1
This class is Mandatory for PROFIBUS-DP Encoders, all functions defined in
this class must be supported by the Encoder. Class 2 functions can optionally
be supported by the class 1 Encoder, these functions must however be
implemented according to this specification. Interoperability is in this case only
guaranteed for the class 1 functions, not for the optional class 2 functions.
1.2 Device class 2
In this class all optional Encoder functions are defined. The class 2 Encoder
must support all class 1 and all class 2 functions.
3. Data Exchange function
3.1 Position value
The Encoder input data are only used for the position value with a mandatory
length of 32 bits, optionally the Encoder supports a position value length of 16
bits. The value is right aligned in the data field.
3.2 Preset function
The preset function supports adaptation of the Encoder zero point to the
mechanical zero point of the system. The preset function sets the actual position
of the Encoder to the preset value. The preset value is written to the Encoder as
output data in the Data_Exchange function. The preset function is used after the
scaling function which means that the preset value is given in the current
measuring units.
The MSB of the preset value controls the preset function in the following way:
Normal operating mode: MSB = 0 (bit 31, optionally bit 15)
The Encoder will make no change in preset value.
Preset mode: MSB = 1 (bit 31, optionally bit 15)
With the MSB = 1 the Encoder accepts the transferred value (bit 0 - 30) as a
preset value in binary code. The Encoder reads the current position value and
calculates an offset value from the preset value and the read position value. The
position value is shifted with the calculated offset value. When the output
position value equals the preset value the preset mode is ended and the MSB can
be set to zero by the master. The offset value can be read with the diagnostic
function and is securely stored in case of voltage breakdown and reloaded at
each start-up.
NOTE! The preset function should only be used at Encoder standstill.