Explanation of CycleCounter monitoring

The terminal must be enabled to recognize whether it has been cyclically supplied with current data. For this PDO CycleCount Activate = TRUE and the PDO CycleCount are to be used cyclically +1. In case of a missing data packet (e.g. by LostFrame) or in case of a frame repetition the terminal increments (+1) a local 8-bit error counter (0...255) in the ESC register 0x030D. By occasionally reading this counter (and setting it to zero if necessary), the application can thus determine, e.g. every second, whether the terminal has detected transmission errors. The reading and writing of the registers must be done by ADS (acyclic communication). If necessary, the sync time of the terminal is to be shifted into a jitter-free range by changing the terminal shift time, where the data transfer from/to the EtherCAT frame is safely possible.

See the TC3 sample program LINK in FB_EL2252 in the action Output_CycleCount, it demonstrates the regular reading of register 0x030D and cumulating the values.