[FAQ] AM62A7: Why is MMC1 powered by two different voltage supplies, VDDSHV0 and VDDSHV5?

The logic state of the MMC1_SDCD and MMC1_SDWP inputs to the host must not change when a UHS-I SD Card changes its IO operating voltage. It is not possible to maintain a valid logic state if these signals propagate through an input buffer of a dual-voltage SDIO cell that changes voltage. So, these signal functions are assigned to IOs that do not change voltage. These signals only connect to switches in the SD Card connector, so there is no reason for them to change voltage when the SD Card signals change operating voltage. The MMC1_SDCD and MMC1_SDWP signals should be connected to the SD Card connector switches and pulled high with external pull resistors connected to VDDSHV0. The other MMC1 SD Card signals with pull-up resistors should have their pulls powered by the VDDSHV5 source that dynamically changes voltage. 

The MMC2_SDCD and MMC2_SDWP pins are powered from the same power rail as the other MMC2 pins. However, you should not use these pins for the MMC2_SDCD and MMC2_SDWP signal functions if you are trying to connect an UHS-I SD Card to MMC2. For this use case, these signal functions would need to implemented using one of the other pin multiplexing options that uses an IO cell powered from a fixed voltage source. The MMC2 assignments are different because we only expected MMC2 to be used with on-board fixed voltage SDIO devices similar to WiFi or Bluetooth transceivers.

Regards,
Paul