Are you asking for B.tech programme? if yes then IIST takes the admission through JEE Advance. IIST admission rank list will be prepared on the basis of JEE Advance Marks. You can check the further information with the given below link.

https://www.iist.ac.in/sites/default/files/admissions/BROCHURE-2018V6.pdf

In case you have any other query then let me know.

Good Luck!