Conditional Formatting or Data Validation for 1 cell based on another but limited data?

What formula or function would tell a cell (D7) that its value has to be a whole number either 1 or 2; or if there is a value in D6 then its value (D7) has to be zero? I would then need to the same for cell D6 where its value has to be whole number either 1 or 2; or it would be zero if no value in D7.

This is for a score card more or less where you can either get points for one factor but not the other.

Thank you!

Thank you for your quick response and I apologize for any confusion.

Please see uploaded document.

The actual cells that I am referring to is that if there is a value in D5, you can not have a value in D6. (this is true for the entire rows of 5 & 6).

In addition I would like to have data validation that will only allow either 1 or 2 to be entered in a cell.

If cell D5 says 2 then cell D6 is zero.

Hope this helps to clarify