How can negative numbers can be represented in fixed point...

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Question by Deepaa
Submitted on 4/2/2004
Related FAQ: comp.dsp FAQ [1 of 4]
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How can negative numbers can be represented in fixed point 24-bit DSP processors. If answer is for Motorola DSP 56k processor I will be more helpful

Answer by bülent
Submitted on 12/7/2004
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if you are going to use such a chip, then clearly the technical reference of the chip would indicate the native data formats it. Now if it does support negatives by hardware you are OK , just use it ( it does not matter fix point or not) but if chip does not support it, you should by software define a sign indicator. The simplest is to assign one bit of each number for sign. This will however decrease the range of numbers by 2.

Answer by David Cary
Submitted on 3/15/2005
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Practically all computers represent negative numbers using two's complement. The Motorola DSP56K is no different. For example: 7FFFFF = 1 - 2^-23 7FFFFE = 1 - 2^-22 ... 400000 = 2^(-1) = +1/2 ... 000003 = 32^-23 000002 = 2^-22 000001 = 2^-23 000000 = 0 FFFFFF = -2^-23 FFFFFE = -2^-22 FFFFFD = -32^-23 ... C00000 = -2^(-1) = -1/2 .... 800001 = -1 + 2^-23 800000 = -1 See the the DSP 56K reference manual http://www.freescale.com/files/dsp/doc/ref_manual/DSP56300FM.pdf for more details. In particular, chapter 3.2.1 "Data Representation". http://en.wikipedia.org/wiki/Signed_number_representations .

Answer by mouse
Submitted on 5/19/2007
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