How to convert binary fraction to integer value in VHDL?

[seffin]

Dear friends..

I have problem with fixed point in VHDL, How to display binary fraction into LCD in decimal value?
example:
1001.1000₂ = 9.5 decimal

1001₂ = 9 and .1000₂ = .5 but 1000₂ in decimal value is = 8.

if I make an encoder for this fraction value it must require very many resource in my FPGA.
I use Spartan 3E board.

please help me..

Regards

Seffin

 

[kalyansrinivas]

Can you subtract a value of 3 (8-3) from the fractional values and display

 

[seffin]

But if the value is 1001.1100₂ the decimal value is 9.75₁₀
the value that result from subtraction is not true..
any body have an idea? :-(

 

[TrickyDicky]

with only 4 fractional bits, there are only 16 possible states, so it is only a 16-1 decoder, which is pretty straight forward.

 

[FvM]

The weight of the lowest fractional bit is 1/16 or 0.0625, so you would need four display digits to represent it exactly. If this is what you want, you can multiply with 625 and convert to decimal. Or just use a look-up table of intended representations with your selected width, as TrickyDicky suggested.

 

[seffin]

Thank you very much FvM and TrickyDicky for your reply... It's very helpful!
If I use 8 bit fraction bit, the lowest fraction bit is 1/256 or 0.00390625, but it have too many digit (8 decimal digit fraction), so how to make it only 2 digit or 4 digit without reduce fraction bit?

 

[TrickyDicky]

you now have a problem of displaying it, not with your actual data.
you will have to decide how many decimal bits are acceptable and a Look up table should suit this problem.

 

[seffin]

TrickyDicky, What you mean with acceptable decimal bits?
I just want to diplay like this:
99.99
if I add with 1 it will display 100.00 decimal.. but I use 8 binary fraction bits..
please help me..

 

[TrickyDicky]

use a look up table for the fractional part. You dont need to do any adding at all.

 

[seffin]

Ok, Thank you for all I'll try it.. if I have succeeded I'll let you know..