Do we need to have transceivers if we support 1.8V IO level on FPGA ? Doesn't have the capability to support the 1.8V ?
And also it requires the PU to 3.3V on these interface. Are these mandatory ?
I see, well since the HPS I/O use a fixed voltage level and cannot be changed dynamically, transceivers are required to support level-shifting and isolation for cards that can operate at 1.8 V.
The SD/MMC cards support various operating voltages, for example 1.8V and 3.0V. If you have a card which is at 1.8V and you eject it and replace it with another card, which is 3.0V, then voltage switching is required. Many SD cards have an option to signal at 1.8 or 3.0 V, however the initial power-up voltage requirement is 3.0V. To support these different voltage requirements, external transceivers are needed.
More information here on page 1721 (Flow Diagram).