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Technical Manual
Absolute Single/Multiturn Profibus Encoders
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PROFIBUS‐DP basics
This description provides information concerning the implementation of the PROFIBUS‐DP transmission protocol
in the slave mode in our devices. It should be noted that the extent of the functions described might be limited
according to the device or application. With protocol conversions in particular, as a rule fewer functions are used!
The profile required
The link between the decentralized process operation and the central control via the communication system
takes place in the lowest hierarchy level on the filed or process bus. At this level, the main requirements are a
simple protocol operation and short data transmission times for the communication. This ensures the fastest
system reaction time to the dynamic states of the peripherals. In addition to the classic data exchange, the acyclic
transmission of parameter, diagnostic and configuration data must be possible, without radically impeding the
real‐time capability of the bus. This is the only way to guarantee the achievement of good diagnostics and safe
operation.
Characteristics
The main task of PROFIBUS‐DP is the cyclic transmission of the process data from the control system to the
peripheral equipment and vice versa. The access procedure uses the Master‐Slave principle. Here in the polling
operation a Master communicates with its assigned slave devices one after the other on the bus. A data exchange
is initiated by a request telegram and ended by an acknowledgement telegram from the Slave concerned. So,
each Slave only becomes active after a call from the Master. This avoids a simultaneous bus access. The hybrid
access procedure of PROFIBUS allows a combined operation of several bus masters and even a mixed operation of
PROFIBUS‐DP and PROFIBUS‐FMS within a bus section. However the pre‐requisition for this is the correct
configuration of the bus system and the unambiguous assignment of the Slave devices to the Masters. PROFIBUS‐
DP distinguishes two types of Master. The Class 1 Master carries out the cyclic transmission of the operating data
and supplies the user data. The Class 1 Master can be addressed by a Class 2 Master using certain functions.
Direct access to the Slaves is not permitted. The functions are limited to support services such as reading the
diagnostic information of the slaves. A Class 2 Master is thus also understood as a programming or diagnostic
device.
Protective functions
PROFIBUS‐DP is equipped with many protective functions. These ensure safe fault‐free communication not only in
the harsh environment of the decentralised peripheral equipment, but also in the case of external interference or
the failure of one or more stations. Wrong parameter settings are recognized directly, in that stations having the
wrong parameters are not integrated in the operating data exchange.
The Master records the failure of any station and indicates this to the user by means of a general diagnostic
message. Any breakdown in the transmission path is detected by the Slave by means of time monitoring and
leads to the outputs being switched off.
EMV disturbances are virtually filtered out by means of the difference signal, thanks to the particularly noise‐
immune RS485 transmission system.
Data transmission errors are recognized thanks to frame and check‐sum controls and lead to the retransmission
of the telegram.
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