FPGA Central

Hello,

I was wondering if there is a way to easily change a bin number to a
bcd without a lookup table or anyhting else like that if the numbers
do not need to convert.

Example: I have a decimal value of 1234 in a 12-bit binary reg. I
would like to transfer those values to a 16-bit bcd. No conversions
needed, I still want 1234, just in bcd. Is there an easy way to do
this?

-Mark

weizbox wrote:

> I was wondering if there is a way to easily change a bin number to a
> bcd without a lookup table or anyhting else like that if the numbers
> do not need to convert.

For small numbers of digits, the amount of logic is
pretty small. It can easily be done in combinatorial
logic.

The work toward a decimal based floating point standard
uses 10 bits to store three digits. It is supposed to take
only a small amount of logic to convert between that and BCD.

Write out the Karnaugh maps and see how much logic it takes.

(There are also logic minimization programs around to do it.)

-- glen

"weizbox" <[email protected]> wrote in message
news:[email protected] om...
> Hello,
>
> I was wondering if there is a way to easily change a bin number to a
> bcd without a lookup table or anyhting else like that if the numbers
> do not need to convert.
>
> Example: I have a decimal value of 1234 in a 12-bit binary reg. I
> would like to transfer those values to a 16-bit bcd. No conversions
> needed, I still want 1234, just in bcd. Is there an easy way to do
> this?
>
> -Mark

How about this for 4 digits: (some of the LSbits can be truncated - I just
haven't done an error analysis or testbench)
wire [22:0] res3;
wire [21:0] res2;
wire [20:0] res1;
wire [19:0] res2;
wore [3:0] bcd3, bcd2, bcd1, bcd0;
assign {bcd3,res3} = bin[12:0] * 14'h20c5; // 5 adds, 4 adders in a tree
assign {bcd2,res2} = res3 * 3'h5;
assign {bcd1,res1} = res2 * 3'h5;
assign {bcd0,res0} = res1 * 3'h5;

The idea here is use a fixed/flaoting-point hybrid. The first thing you'd
like is to "effectively" divide by 1000 which - though close at 131/131072
(131/2^17) provides better results at 8389/8388608 (8389/2^23). The first
BCD digit is the multiplied result shifted 23 bits. The fractional part is
effectively multiplied by 10 ("fractional" multiplied by 5 and shifted 1)
to get the next digit 22 bits out.

The implementation looks better in code and can be manipulated further for a
smaller implementation with the appropriate error analysis.

The idea is the same in software: find the first digit by dividing by 1000
(or 10000, whatever) then get successive digits from 10x the fractional
part.

In article <LOi9d.24$[email protected]>,
John_H <[email protected]> wrote:

>How about this for 4 digits: (some of the LSbits can be truncated - I just
>haven't done an error analysis or testbench)
>wire [22:0] res3;
>wire [21:0] res2;
>wire [20:0] res1;
>wire [19:0] res2;
>wore [3:0] bcd3, bcd2, bcd1, bcd0;
>assign {bcd3,res3} = bin[12:0] * 14'h20c5; // 5 adds, 4 adders in a tree
>assign {bcd2,res2} = res3 * 3'h5;
>assign {bcd1,res1} = res2 * 3'h5;
>assign {bcd0,res0} = res1 * 3'h5;

That's lovely, makes me realise I ought to study _Hacker's Delight_
(by Henry S Warren, for those unfortunates who haven't read it yet)
more. Its tricks no longer seem quite so relevant on CPUs with
two-cycle 64x64->128 multipliers, but they're going to be really handy
on FPGA.

Tom

"weizbox" <[email protected]> wrote in message
news:[email protected] om...
> Hello,
>
> I was wondering if there is a way to easily change a bin number to a
> bcd without a lookup table or anyhting else like that if the numbers
> do not need to convert.
>
> Example: I have a decimal value of 1234 in a 12-bit binary reg. I
> would like to transfer those values to a 16-bit bcd. No conversions
> needed, I still want 1234, just in bcd. Is there an easy way to do
> this?
>
> -Mark

I just did a quick google - always nice to do *first* - and found
http://www.opencores.org/projects.cg...o_bcd/overview

Check it out for your needs. (it took me a moment to find the "Downloads"
in the top right corner).

"John_H" <[email protected]> wrote in message news:<PtD9d.33$[email protected]>...
> "weizbox" <[email protected]> wrote in message
> news:[email protected] om...
> > Hello,
> >
> > I was wondering if there is a way to easily change a bin number to a
> > bcd without a lookup table or anyhting else like that if the numbers
> > do not need to convert.
> >
> > Example: I have a decimal value of 1234 in a 12-bit binary reg. I
> > would like to transfer those values to a 16-bit bcd. No conversions
> > needed, I still want 1234, just in bcd. Is there an easy way to do
> > this?
> >
> > -Mark
>
> I just did a quick google - always nice to do *first* - and found
> http://www.opencores.org/projects.cg...o_bcd/overview
>
> Check it out for your needs. (it took me a moment to find the "Downloads"
> in the top right corner).


Thanks for pointing out the download link! I was actually there but
didnt see the downloads, all I saw was no files in CVS thing and since
the dev status was in "planning" that the file wasnt available! Thanks
a lot!

-Mark