1. A speculative command decode serial interface device comprising: a command decode register configured to decode a high-order portion of command bits input on a serial input pin coupled to the command decode register and speculatively produce a non-memory read command; at least one data register for retaining data associated with a corresponding non-memory read command; an interface logic block configured to produce a selection of non-memory read data and enable output of non-memory read data from the serial interface device, the interface logic block coupled to the command decode register and the at least one data register; a data multiplexer configured to provide read data from a selected one of the at least one data registers, the data multiplexer coupled to the at least one data register and the interface logic block; a data sequencer configured to queue read data, the data sequencer coupled to the interface logic block and the output of the data multiplexer; and an output register configured to output read data based on an enabling indication from the interface logic block, the output register coupled to the data sequencer and the interface logic block.