TCC (Time Clock Control) functions for AC500?
You can use this simple equation for your own FB:
spring_day := (14 - (1 + REAL_YEAR*5/4) MOD 7);
aut_day := (7 - (1 + REAL_YEAR*5/4) MOD 7);
spring_day := (31-(5* REAL_YEAR/4+4) MOD 7);
aut_day := (31-(5* REAL_YEAR/4+1) MOD 7);
Be aware of different time of change, most commun in Europa are 2AM to DST at 3AM from DST.
I think oscat.de has an FB for europa.