If teams A to G are the first group, and teams H to N are the second group then you could use the following schedule where the 7 rounds are the rows and the 7 games are the columns.
G1 G2 G3 G4 G5 G6 G7
R1 (A H) (L M) (K I) (C F) (N J) (B G) (D E)
R2 (E F) (B I) (M N) (L J) (D G) (H K) (C A)
R3 (D B) (F G) (C J) (N H) (M K) (E A) (I L)
R4 (J M) (E C) (G A) (D K) (H I) (N L) (F B)
R5 (G C) (K N) (F D) (A B) (E L) (I J) (H M)
R6 (I N) (A D) (L H) (G E) (B C) (F M) (J K)
R7 (K L) (J H) (B E) (M I) (A F) (C D) (G N)
Pairs of teams within the same group all play each other once, while each team has exactly one between-group game (the 7 games on the main diagonal). If you don't want the inter-group games, then just give these teams a bye.
