I have a question about the scan cycle

Time 

As per my information every plc can execute number of instructions per ms 

In case of  ob38  cycle interrupt is 3ms  and the internal logic takes longer time than the 3ms what will happen at this point 

Will the plc call ob38 again without finishing the last scan

When also the plc can execute the other ob if it execute ob every 3ms

Hi fsoliman355,

The following information can be found in the documentation:

Call of error OBs in connection with cyclic interrupt OBs

The runtime of a cyclic interrupt OB must be significantly smaller than its time interval. Otherwise, it could still happen that the time interval of a cyclic interrupt has expired but the corresponding cyclic interrupt OB is still being processed. In this case, the operating system generates a time error (calls OB 80). The cyclic interrupt that caused the error is executed later or discarded. However, only one cyclic interrupt OB for each priority can be executed later.

Kind regards
Stefan