BECKHOFF BK3xx0 - Manual (Page 13)

Notes on the Documentation
Fieldbus Components 11
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 terminals can be used within one terminal strip. 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.