NIT Trichy is a prominent Indian institute matching the world standards in the group of NIT'S. I think you can get the seat in nit with this this percentage in sc/st category. It may depend on others percentage also. For suppose some other people also got 80 percent as like you, but there's  a difference in the rank. So they compare the two ranks and take the highest rank. For other categories u must need to score 93 percent above.