Daisy chaining of serial I/O interface on stacking devices

摘要

A bottom die and a top die stacked on the bottom die are configured to provide a daisy chain function. Both die include an input/output function control bonding pad ( 20 G), a first bonding pad ( 20 C) controllable to function as either an input or an output, and a second bonding pad ( 20 E) controllable to function as either an output or an electrically floating pad in response to a corresponding input/output function control signal. The top die ( 30 ) is stacked on the bottom die ( 20 ) and the first bonding pad ( 20 C) of the bottom die ( 20 ) is wire bonded to the first bonding pad ( 30 C) of the top die ( 30 ). A first reference voltage (VDD) on the function control bonding pad of the bottom die configures its first bonding pad as an output and its second bonding pad as electrically floating, and a second reference voltage (VSS) on the function control bonding pad of the top die configures its first bonding pad as an input and its second bonding pad as an output, to thereby provide the daisy chain function.