Sean “P. Diddy” Combs and NBA Hall of Famer Earvin “Magic” Johnson will be launching networks on cable TV systems in the next two years.

Diddy’s network, called Revolt, will have programming fueled by music and pop culture, influenced by the nonstop chatter of social networking Web sites. It is the latest of several challenges to MTV and BET, both owned by Viacom.

Johnson’s channels, named Aspire, will target African-American families with positive, aspirational programming.

These networks and six more as-yet-unannounced channels will be carried by Comcast.