# Calculating Percentages in VHDL?

Discussion in 'VHDL' started by Cory Shol, Jan 22, 2014.

1. ### Cory SholGuest

Hello all,

I am working on a project that needs to complete safety crosschecks on a regular basis.

If a User sets up the equipment at a specific setting the FPGA logic will calculate a Reference Voltage (lets say a 16 bit number ). The user will also set a percentage from 10-35% (Overvoltage Threshold).

Once the user says he wants the system to allow 15% of overvoltage.

I want to calculate in the logic the 16 bit referance voltage * .15 .

How does one go about calculating percentages? I am using a Xilinx Spartan 3a 700a. A link to an tutorial or algorithm would be great.

Thanks

Cory Shol, Jan 22, 2014

R * 0.15 = R * (0.15 * 2^17) / 2^17

3. ### Cory SholGuest

Ahh yes , I actually just thought about something similar to that just before I read the reply. Sometimes your brain doesn't work as fast as you want it to.

Cory Shol, Jan 22, 2014
4. ### AndyGuest

Try the fixed point library in VHDL. It is included in the 2008 standard, and a quick google search will get you the vhdl fixed point user guide that shows you how to use it.

Andy

Andy, Jan 22, 2014