| 摘要 |
A method and apparatus are shown for increasing a propagation delay that may be tolerated between a memory controller and a memory device. The present invention provides for selection between two data paths for each word, where a first data path latches the data word from a DQS domain on a falling edge of a CLK0 domain and a second data patch latches the data word from the DQS domain on a rising edge of the CLK0 domain. Selection of the first data path permits larger relative propagation delays between the controller and memory to be accommodated without loss of data. Further, multi-cycle source synchronous timing logic may be employed that provides for the capture of data words on rising and falling edges of successive cycles o the DQS domain and storage for an additional cycle of the DQS domain to extend the period of time that each data word from the DQS domain is available and valid for the CLK0 domain. Selection of the first data path may also be used to accommodate shorter relative propagation delays between the controller and memory without loss of data when the propagation delay is short enough that the data from the memory is valid in advance of a first falling edge of the CLK0 domain by a margin that is at least a set-up time interval for the controller. |
