I'm not interested in bitcoin mining , I just want to generate sha256 hash of all possible input string of 64 characters length , can I use bitcoin mining hardware just to generate just sha256 hash for my personal use?
Most bitcoin ASICs take as input a SHA256 chaining value and a 480-bit block, and they try every possible 32-bit suffix to check if SHA256(SHA256(block + suffix)) begins with sufficiently many zero bits.
So, it won't be easy to do what you want to do (crack a password?).
There are use cases where this limited functionnality is sufficient though, see the 3SUM-pool for instance (disclaimer : it's mine).