If it does not matter what digital value is converted to analogue, you can invent any value for conversion which might be convenient.
If it does matter what digital value is converted to analogue, then the requirements of your project or design should guide you.
Does this make sense?
If perhaps I misunderstand your question, then this excerpt from the New Users Forum README thread might be helpful to you:
care and feeding of ADC, pre-amp, and DAC on many Xilinx development boards link#1 link#2 link#3 link#4
-- Bob Elkind
SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369
Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
