Patent attributes
Read interface circuitry is disclosed that facilitates using a source-synchronous clock signal to calibrate the read interface. In one embodiment, configurable read interface circuitry allows a particular read path to be configured for use in calibrating a read interface of the destination device. In particular, a plurality of read paths are provided, each read path having a configurable multiplexor (“mux”) coupled to a capture register of the read path such that the mux can be configured to select either an input coupled to an inverted output of the capture register or an input coupled to a prior register in the read data path. When the inverted output of the capture register is selected, a source-synchronous clock signal (e.g., DQS or delayed DQS signal) provided at the capture register's clock input results in a toggle signal at the capture register's output. In one embodiment, that toggle signal is provided to a re-sync register clocked by a re-sync clock signal. This toggle signal, together with another toggle signal generated at a toggle register coupled to the re-sync clock signal, are compared for various possible phases of the re-sync clock signal to determine a preferred phase of the re-sync clock signal. For other read paths, a mux coupled to a similar capture register is configured to select an input coupled to a prior register in the read path so that the read path can act as a path for incoming data signals (e.g., DQ signals).
