Dear ftsolutions, thank you for your response.Actually, FTHETA is never reset. my question is that THETA itself overflow every cycle ( output voltage cycle, 5ms). why it does not lead to trap? another question is float is 32-bit variable up to 6.8*10^38, considering DELTETA,.... it should be saturated in longer time. The third question is why this kind of behavior? I mean first control of a few least significant bits are lost then higher bits and at last saturation. why not strightforward to saturation? I am confused!!!