Use Amount or Percentage as an input and both have to update each other

Hello!
I built a calculator in Excel 2010. It works perfectly until I had to add an additional input to be used as a percentage of down payment instead of the essential input which is amount of down payment.
Successfully do that, I can use either one and both have to update each other.
This is because sometimes I need to input a percentage and straightforward know the amount rather than estimate the percentage based on multiple tries of input the amount.

Is there a function,trick or workaround to let that happen and let Excel continue calculation of rates and rest of outputs?

Thank you for assistance,

I seriously doubt it. I heard of this possible through VBA but, again It would definitely cause a cyclic redundancy error for sure.
I will suggest two sheets 1 for entering one value
other for other.