# 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

On Wed, 22 Jan 2014 08:52:10 -0800 (PST)
Cory Shol <> wrote:

> 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
>

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

--
Rob Gaddi, Highland Technology -- www.highlandtechnology.com
Email address domain is currently out of order. See above to fix.

3. ### Cory SholGuest

On Wednesday, January 22, 2014 11:45:33 AM UTC-6, Rob Gaddi wrote:
> On Wed, 22 Jan 2014 08:52:10 -0800 (PST)
>
> Cory Shol <> wrote:
>
>
>
> > 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

>
> >

>
>
>
> R * 0.15 = R * (0.15 * 2^17) / 2^17
>
>
>
> --
>
> Rob Gaddi, Highland Technology -- www.highlandtechnology.com
>
> Email address domain is currently out of order. See above to fix.

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