Profibus Introduction; Profibus Dp - Beckhoff BK3 0 Series Documentation

K-bus
The K-bus is the data path within a terminal strip. The K-bus is led through from the Bus Coupler through all
the terminals via six contacts on the terminals' side walls. The end terminal terminates the K-bus. The user
does not have to learn anything about the function of the K-bus or about the internal workings of the
terminals and the Bus Coupler. Many software tools that can be supplied make project planning,
configuration and operation easy.
Potential feed terminals for isolated groups
The operating voltage is passed on to following terminals via three power contacts. You can divide the
terminal strip into arbitrary isolated groups by means of potential feed terminals. The potential feed terminals
play no part in the control of the terminals, and can be inserted at any locations within the terminal strip.
Up to 64 Bus Terminals can be used in a terminal block, with optional K-bus extension for up to 256 Bus
Terminals. This count does include potential feed terminals, but not the end terminal.
Bus Couplers for various fieldbus systems
Various Bus Couplers can be used to couple the electronic terminal strip quickly and easily to different
fieldbus systems. It is also possible to convert to another fieldbus system at a later time. The Bus Coupler
performs all the monitoring and control tasks that are necessary for operation of the connected Bus
Terminals. The operation and configuration of the Bus Terminals is carried out exclusively by the Bus
Coupler. Nevertheless, the parameters that have been set are stored in each Bus Terminal, and are retained
in the event of voltage drop-out. Fieldbus, K-bus and I/O level are electrically isolated.
If the exchange of data over the fieldbus is prone to errors or fails for a period of time, register contents (such
as counter states) are retained, digital outputs are cleared, and analog outputs take a value that can be
configured for each output when commissioning. The default setting for analog outputs is 0 V or 0 mA. Digital
outputs return in the inactive state. The timeout periods for the Bus Couplers correspond to the usual
settings for the fieldbus system. When converting to a different bus system it is necessary to bear in mind the
need to change the timeout periods if the bus cycle time is longer.
The interfaces
A Bus Coupler has six different methods of connection. These interfaces are designed as plug connectors
and as spring-loaded terminals.
2.5

PROFIBUS introduction

2.5.1

PROFIBUS DP

In PROFIBUS DP systems a master (PLC, PC, etc.) usually communicates with many slaves (I/Os, drives,
etc.); only the master actively accesses the bus (by sending unsolicited telegrams), while a DP slave only
sends telegrams when requested by the master.
DP StartUp
Before the master and slave can cyclically exchange data, the parameter and configuration data is
transmitted from the master to the slaves during the DP StartUp phase. After the parameter and
configuration data has been sent, the master interrogates the slave's diagnostic data until the slave indicates
that it is ready for data exchange. Depending on the scope of the calculations the slave has to carry out as a
result of receiving parameter and configuration data, it may take several seconds before it is ready for data
exchange. For this reason the slave possesses the following states.
Parameter data
The parameter data is sent from the master to the slave in the SetPrmLock request telegram. The
SetPrmLock response telegram does not contain any data, and therefore consists of a single byte, the short
acknowledgement. The parameter data consists of DP parameters (e.g. the setting of the DP watchdog or
BK3xx0 Version: 4.3.0
Product overview
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