BECKHOFF BC8000 - Manual (Page 34)

Questions and Answers
34 BC8000
Solution
Your program takes longer than 100 ms. Because the internal K-Bus runs
synchronous with your PLC program, it is no longer triggered early enough,
and the Bus Terminal watchdog becomes active. This can be rectified by
triggering a short refresh of the K-Bus. The setting can be carried out with
the KS2000 software.
Table 1 register 17
LowByte cycle time to K-Bus refresh (<= 80 ms)
HighByte Retries
Recommendation Enter 0x0350 in table 1, register 17, i.e. three retries, all at 80 ms.
Note that this causes the Bus Terminal watchdog to increase to 240 ms
during a fault condition (this is not true in case of a K-Bus error, where the
watchdog will remain at 100 ms).