Systems, methods, and apparatus are described that enable a serial bus to be operated in multiple modes that employ additional wires for communicating data such that the bus width may be dynamically extended to improve bandwidth and/or throughput. One method includes transmitting a set of frames or sequences of symbols configured to carry up to a maximum number of data bytes over the serial bus, transmitting control signaling over a first data lane and the clock lane after the set of frames or sequences of symbols has been transmitted, and transmitting a first signal over a second data lane while transmitting the control signaling that may indicate whether the set of frames or sequences of symbols includes padding. The first signal may indicate a number of valid bytes or words in the set of frames or sequences of symbols.