I am doing my own hardware design based on the MicroZed. I am looking at the DDR3 implementation, and found a couple of design choices made on the MicroZed that I did not understand. I am using the Rev F schematic.
I would appreciate it very much if someone could tell me why the following choices were made:
1. Why is 1.5V used for the DDR voltage? DDR3L memory is used. This requires 1.35V for VDD. 1.5V is used on DDR3 and the part used on the MicroZed is 1.5V compatible. Also look at my second question which is related to this.
2. The Vivado Board Definition file for the Microzed selects "DDR3 (Low Voltage)" as the memory type. This selects 1.35V interface, and specifically sets the internal reference voltage. The Board Definition file also selects "Internal Vref". Does this combination not set the wrong reference voltage?
3. Why does the board definition file select "Internal Vref"? The hardware is design to use the external reference (pins H6 and P6 on U9J connected to VTTREF) and according to the Xilinx documentation, it should be used because it provides better performance.