Shield IOTYPE are provided for “soft ground” pins to improve the localized references. These are actual I/O pins that are re-purposed to isolate switching noises around high-speed I/O interfaces. Shields are only implemented on memory interfaces on the unused DQ bits in specific device/package combinations. This rule applies to GPIO and HSIO based DDRx memory interfaces. For maximum shielding benefit, it is recommended to tie these SHIELD signals to VSS on the board for the specific device/packages included in the PPAT description.