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  1. @[email protected] Many thanks to you. I found out that the ram on the Nexys 4 can actually save the data during the process I wrote the .bit file into the board. I will try your method, and I think it can be really helpful if I learned how to use it. Now the cpu is working well and I'm really grateful for your help.
  2. @[email protected] Thanks a lot for your approach, really. I generated 3 .bit files. The 3 .bit files are write_instructions.bit, test_write_instructions.bit and cpu.bit. After writing and executing write_instructions.bit on nexys 4, I wrote and executed test_wtite_instructions.bit. It turned out that I wrote the instructions into the ddr2 memory successfully. Even after I reprogrammed nexys 4 using test_writing_instructions.bit, the data in ddr2 memory is still there. But after I reprogrammed nexys 4 using cpu.bit, the data in ddr2 memory is gone. How did this happen? Could you please explai
  3. I'm writing a cpu on Nexys 4 DDR, but I have a problem: The DDR2 memory on Nexys4 will be reset whenever a new .bit file is written to the FPGA. I have already generated two .bit files. One is to write instructions and data to the DDR2 memory, and the other is the cpu program. What should I do to make the DDR2 memory remain the same even after it's programmed? Thank you!