Will covered call strategy also entails interest


I read that I can pledge my stock and trade in derivatives. However, it is mentioned that I can only use 50% of the margin required for taking position in an option contract. I really fail to understand why this is so because the value of pledged shares even after the haircut will be far more than the margin required for position in options contract. Be that as it may, I request someone to confirm if this 50% restriction applies even to covered call. For example can I take a position in SBI 290 or 300 call after pledging 3000 shares of SBI (One lot) without bothering about the cash margin? Many friends tell me that they are doing this without interest implications from other brokers including discount brokers.