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Participant
16,221 Views
Registered: ‎07-11-2009

## Implementing fixed point arithmetic in VHDL

Hi, I'm trying to implement a fixed point multiplication in VHDL targeting Xilinx V2Pro board using xilinx ISE 10.1. Can anyone suggest me how I can do it? I got two variables a and b, where for example a=3.24 and b=-1.6. How can I represent these numbers in fixed point and how can i get them multiplied?

Milan

3 Replies
Teacher
16,204 Views
Registered: ‎08-14-2007

Hi Milan,

if you don't even know how fixed point numbers are calculated from floating point numbers you should join a class for digital basics first.

Have a nice synthesis

Eilert

Participant
16,192 Views
Registered: ‎07-11-2009

Hi Eilert !

My question is about implementing the fixed point multipication in VHDL. I'm sorry if I gave u an impression that i don't know how to calculate the fixed point from floating. Now, back to my question, how can I implement it in VHDL with Xilinx for V2pro board?

Teacher
16,178 Views
Registered: ‎08-14-2007

Hi Milan,

well, you really gave that impression. Sorry.

Fixed point arithmetic works just like ordinary binary arithmetic. It's the same hardware.

You only have to care where your fixed point is after the calculation.

eg:

you want to multiply 1110.1101 (14.8125) by 0011.0100 (3.25)

so your result will be :

00110000.00100100 (48.140625)

So when you have 4 decimal places in each operand, the result has 8 decimal places.

If you want your result to have the same accuracy as your inputs you can drop some decimal places by truncation or rounding.

You have to keep your integer bits.

Or you can do scaling. That is, you use the 8 MSBs and drop the rest. You treat these 8 bits still as a fixed point number, but for your calculation you keep in mind that it is actualy divided by 16 (and the lower 8 bit truncatet).

So the only thing you have to worry about is your numerical range and the interpretation of your result.

The hardware elements are unchanged.

Have a nice synthesis

Eilert