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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: DSP 2's complement vs straight binary
References: <3DAF9910.914BA71C@webaccess.net> <email@example.com>
Date: Fri, 18 Oct 2002 06:22:34 GMT
NNTP-Posting-Date: Thu, 17 Oct 2002 23:22:34 PDT
> Chuck Simmons firstname.lastname@example.org
> >You unkindly deleted the table I laboriously created with my ten
> >incredibly nimble thumbs. However, reference to that table will quickly
> >show that the column of signed decimal numbers I gave converts using 2's
> >complement exactly to the column of 2's complement numbers obtained from
> >the original binary column by means of inverting the MSB. The method is
> >used for A/D and D/A converters where the mid binary code corresponds to
> >the common mode or zero.
> Cute. That last sentence was the key I needed. And it would be a new meaning
> for 2's complement, at least for me.
> Thanks for the update.
> This does generate a question though.
> Is there some particular advantage in using this common mode/zero method
> or is it just convenient in some situations.
No. The last chip design architecture I worked on I hammered away on
getting inverters. They are cheap! Just about a square micron or less.
No effect on competative edge, after all. They argued with me until I
submitted and ate the extra instruction. The adavantage, if any, is that
the SAR in the ADC is binary. I don't mind. I just want a little
inverter. I will surely go through that exercise again another day.
To think. 25 years ago, Burr-Brown had some conversion products with an
XOR built in so you could choose. We seem to have gone backward from
> Ok I put your table back in:) Happy now?
Yes. I created the table because the MSB inversion is not really
intuitive as we have seen.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons email@example.com
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