Method and apparatus for prioritizing outbound data transfers across a serial data transmission interface to a connected device. An interface circuit includes a memory block in which outbound frames are temporarily stored pending transfer to the connected device, the outbound frames characterized as single frames having a command word payload and data frames which include a user data payload. A port successively establishes connections with corresponding ports of the connected device in response to connection requests associated with the outbound frames in the memory block. A prioritization circuit places single frame connection requests into a first queue and data frame connection requests into a second queue. Single frame connection requests are further placed into the second queue when the port fails to establish a successful connection. The connection requests in the first queue are forwarded to the port before the connection requests in the second queue.