Deductions & credits

HI Thanks.  Couple of question.  In turbo tax there is a federal review.  When this federal review is completed, I assume it knows that I am taking the standard deduction.  At that point I am still receiving the 600 cash contribution after the federal review has been completed.  After State review is completed turbo tax does a final review.  It is at the final review stage that the 600 is changed back to 300.   Are there any other limits on the 600 besides cash.  I have more than $600 listed as cash contributions.