Beckhoff BK3120 User Manual

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PROFIBUS DP communication

BK3xx0 55Version: 4.3.0

Fig.42: K-bus - synchronous mode with optimized input update (one cycle)

The delay time is set by means of the UserPrmData [}35] (in µs, in Motorola format). The extended GSD file

of the Bus Coupler is, however, necessary for this:

Byte Value: Description

13 Delay time (in µs) high byte

14 Delay time (in µs) low byte

Synchronous mode with optimized input update (two cycles)

In the third mode of synchronous operation, the advantages of the other two operating modes are combined.

Two K-bus cycles are carried out within one DP cycle. The first cycle begins immediately after reception of

the Data_Exchange telegram from the master, which means that the outputs are generated as quickly as

possible. The second cycle is started after a delay time that begins after completion of the first cycle has

elapsed, so that the inputs are as recent as possible. It is important here to ensure that two times the

duration of the K-bus cycle, plus the delay time, plus approx. 20% (to allow for the lower priority processes

on the coupler) is shorter than the DP cycle time (which, under TwinCAT, means the cycle time of the

associated task).

Fig.43: K-bus - synchronous mode with optimized input update (two cycles)

The delay time is set by means of the UserPrmData [}35] (in µs, in Motorola format). The extended GSD file

of the Bus Coupler is, however, necessary for this:

Byte Description

13 Delay time (in µs) high byte

14 Delay time (in µs) low byte

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 [}35], and must be entered as the

module in the CfgData. The extended GSD file for the Bus Coupler is, however, necessary for this:

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Beckhoff BK3120 Specifications

General