6.11.3.12 DDR2/mDDR Boundary Scan Limitations

Due to DDR implementation and timing restrictions, it was not possible to place boundary scan cells between core logic and the IO like boundary scan cells for other IO. Instead, the boundary scan cells are tapped-off to the DDR PHY and there is the equivalent of a multiplexer inside the DDR PHY which selects between functional and boundary scan paths.

The implication for boundary scan is that the DDR pins will not support the SAMPLE function of the output enable cells on the DDR pins and this is a violation of IEEE 1149.1. Full EXTEST and PRELOAD capability is still available.