I used R9 280 and R9 270 for cross fire. Actually both cards ware detected by system but crimson system showed master card(280) is enable but second one(270) is disable!? I want to turn on cross fire option from Radeon Settings > Gaming > Global Settings but found nothing!! even i exchange two cards also the same. Always second card disable. by the way i used one cross fire line.
Board: Giga GA-970A-D3P