Up counter maximum counts

Hello friends i have a question about using counters 

What is the maximum counts can the up counter count at the s7 1500 and what happens after exceeding the max 

While a maximum value of 999 holds true for the legacy counters, you can (and arguably should) use IEC counters (i.e. CTU, CTD or CTUD).

You can with these also decide to use SINT, UINT, UDINT (1200's and 1500's) or even ULINT (1500 only) as their datatype.

A 64bit ULINT will allow you count up to maximum 18446744073709551615 so you probably won't have to worry about what happens if you reach that value (it will simply stop counting though should you reach it)