BECKHOFF BK3xx0 - Manual (Page 54)

Notes on the Documentation
52 Fieldbus Components
Dummy output byte
The Bus Coupler's PROFIBUS DP ASIC can only generate an interrupt after reception of a
Data_Exchange telegram if output data has been received. This means that at least one output byte must
be transferred via DP in synchronous mode. If only input terminals are plugged in, and no output data is
therefore present, a dummy output byte can be configured. It is activated in the UserPrmData, and must
be entered as the module in the CfgData. The extended GSD file for the Bus Coupler is, however,
necessary for this:
Byte Bit Value Description
3 5 1
bin
Dummy output byte activated
It is also necessary for the dummy output byte to be configured in the CfgData before the complex
terminals:
CfgData DP modules
0x20 Dummy output byte
K-Bus cycle counter
In order for the master to be able to check reliably whether precisely one (or two) K-Bus cycles are
always being carried out during one DP cycle, a K-Bus cycle counter can be transferred in the input data
from the Bus Coupler to the master. This is incremented after each K-Bus cycle (0 is omitted, so that 1
follows after 255). The K-Bus cycle counter must be activated in the UserPrmData and entered as a
module in the CfgData. The extended GSD file for the Bus Coupler is, however, necessary for this:
Byte Bit Value Description
3 3 1
bin
K-Bus cycle counter activated
It is also necessary for the K-Bus cycle counter byte to be configured in the CfgData before the complex
terminals:
CfgData DP modules
0x10 K-Bus cycle counter