You could use the schedule below. But note that if teams A to H are division 1 and teams I to P are division 2, then every meeting is interdivisional. You don't necessarily have to tell the teams of this structure, but if you can assign teams so that the average ability of the divisions is about the same, then you will make the tournament more fair.
G1 G2 G3 G4 G5 G6 G7 G8
round 1 (P A) (N F) (L B) (J E) (M C) (O H) (I D) (K G)
round 2 (N E) (P B) (J F) (L A) (O G) (M D) (K H) (I C)
round 3 (L D) (J G) (P C) (N H) (I B) (K E) (M A) (O F)
round 4 (J H) (L C) (N G) (P D) (K F) (I A) (O E) (M B)
round 5 (M G) (O D) (I H) (K C) (P E) (N B) (L F) (J A)
round 6 (O C) (M H) (K D) (I G) (N A) (P F) (J B) (L E)
round 7 (I F) (K A) (M E) (O B) (L H) (J C) (P G) (N D)
round 8 (K B) (I E) (O A) (M F) (J D) (L G) (N C) (P H)