SD initialization and booting of the PS is completed at 3.3V in high-speed mode. After initialization, the SD interface (command, data, and clock) operates at 1.8V to support the ultra high-speed (UHS) SD cards. The highest speed modes are only supported when the bank voltage is 1.8V.
Dynamic switching from 3.3V to 1.8V is required on the host and the SD interface. This Figure shows the SD voltage switching sequence diagram.
The voltage translation function is implemented by an external voltage level translator as shown in This Figure.
After the boot up, the SEL pin is used to switch from 3.3V to 1.8V to operate at the highest speed modes of the SD cards (Table: SD Card Speed Modes(1)). The SEL pin is automatically driven by the controller if configured in SD3.0.
IMPORTANT: Voltage level shifters are only used for SD cards. SD interface voltage translation is only applicable to SD UHS cards.
Note: The SDx_DIR0 and SDx_DIR1 direction signals might not be required for all devices. For additional information, refer to the Versal ACAP PCB Design User Guide (UG863) and verify with device vendor