cutoffs of JEE 

For General caategory - 250 to 300 AIR

for SC and OBC NCL - 7000 to 8000 AIR

for ST - somewhere around AIR 40000 

for KM(kashmiri migrant) - AIR 5000 to 6000

for PwD - AIR 5000 to 6000

you can also apply through JEE Mains (AIRs)

General category - No admission through JEE Mains

OBC NCL - 5000 to 8000

SC - 5000 to 6000

ST - around 40000

KM - 5000 to 6000

PwD - 5000 to 6000

(All ranks mentioned are not category ranks)

All the best!

To get into IISC you require a rank under 250 if You belong to general category, With relaxation to other categories as per rules. For other categories, it is as follows

OBC 6000

SC 8000

Note that this are all India ranks not Category ranks , So You need to work really hard to get into IISC.

For general category 

Your rank should within 1 - 250 to get admission into IISC .