Calculating Percentages in VHDL?

[Cory Shol]

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]

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 <cory.shol@gmail.com> 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.

 

[Andy]

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

 

[Rob Gaddi]

On Wed, 22 Jan 2014 08:52:10 -0800 (PST)
Cory Shol <cory.shol@gmail.com> 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.