BECKHOFF BK3xx0 - Manual (Page 84)

Notes on the Documentation
82 Fieldbus Components
Implementation Levels of the Bus Coupler in Multi-
Configuration Mode
Structure of a production machine
Production machines often consist of a machine part that is always present in the machine and of machine
extensions that may be added as options. This division also usually applies as well both to the software (the control
program) and to the hardware (the necessary process signals via Beckhoff Bus Terminals) associated with the
machine. A machine, with machine extensions A, B and C, whose process signals are to be read or output over the
PROFIBUS DP through Beckhoff Bus Couplers BK3110, BK3120 or BK3520, could be structured as follows:
The machine illustrated consists of a controller (e.g. TwinCAT, S7-400, etc.), a PROFIBUS DP master interface (e.g.
FC3101, CP???, etc.) that sends or receives the process signals over the PROFIBUS DP, and of Bus Couplers with
Bus Terminals that form the interface to the machine process. The areas shown in grey relate to machine parts that
are always present. The machine extensions A, B and C are shown in red, green and blue. It can be seen that each
machine extension is associated both with software modules within the control program and process signals that are
connected to the controller via Bus Terminals.
Because the machine builder will not want to maintain eight different control programs for all possible combinations of
the machine extensions, it is helpful if the control program is designed in such a way that the necessary software
modules are activated according to whichever machine extensions are in fact being used. In order to create a control
program suited to all implementation levels of the machine it is however necessary for the same process signals
always to appear at the same addresses in the controller's process image, independently of which process signals
are in fact present in the relevant implementation level. For conventional DP slaves, a different configuration of the
PROFIBUS DP master interface is necessary in such cases. The following sections explain how this problem can be
solved with Beckhoff Bus Couplers, using a single configuration of the PROFIBUS DP master interface.
The advantage of this solution is that two machine configurations only differ in terms of the hardware used (machine
components and Bus Terminals), but not in terms of the software. If the machine is upgraded, it is only necessary for
the additional Bus Terminals to be inserted and wired-up, and for the relevant extension to be activated (e.g. via the
man-machine interface to the machine). Software changes are no longer required.