Hi Abhishek 

ISAT  was conducted to get admission in IIST. But from 2013 it was scrap and now scores of jee advance are basis of  admissions. 

Candidates who are desirous to join B.Tech Programs in IIST must appear for the Joint Entrance Examination Main conducted by Central Board of Secondary Education ( CBSE ), New Delhi to qualify themselves to appear for Joint Entrance Examination Advanced conducted by IITs and secure the minimum prescribed category-wise marks in JEE Advanced 2018 as given below :

General Candidates ( GEN ) : At least 20% ( i.e.73 marks out of 366 ) marks in aggregate and at least 5% ( i.e. 6 marks out of 122 ) marks in each of the three subjects ( Physics, Chemistry and Mathematics ).

Other Backward Community – Non Creamy Layer ( OBC-NCL ) Candidates: At least 18% ( i.e. 65 marks out of 366 ) marks in aggregate and at least 4.5% ( i.e. 5 marks out of 122 ) marks in each of the three subjects ( Physics, Chemistry and Mathematics )

Scheduled Caste ( SC ), Scheduled Tribe ( ST ) & Persons with Disabilities ( PD ) Candidates : At least 10% ( i.e.36 marks out of 366 ) marks in aggregate and at least 2.5% ( i.e. 3 marks out of 122 ) marks in each of the three subjects ( Physics, Chemistry and Mathematics )

Thanks 

All the Best