A serial transmission protocol and architecture are provided that can be used to transmit uncompressed multimedia (e.g., video/audio/control data) over a high speed serial forward communication channel. A backward channel is also provided, for communicating control data. The protocol is implemented with a flexible packet format that supports all different modes of video data, and also supports 24 bit and 30 bit video data (or higher). An example application where the architecture and protocol can be used is a home entertainment multimedia system. A mechanism to implement EDID pass-through and protocols such as HDCP is also provided.