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Introduction to DSP - DSP processors: Motorola processors

The problem of fixed point processors is quantisation error, caused by the limited fixed point precision. Motorola reduce this problem in the DSP56002 by using a 24 bit integer word length:


They also use three internal buses - one for program, two for data (two operands). This is an extension of the standard Harvard architecture which goes beyond the usual trick of simply adding a cache, to allow access to two operands and the instruction at the same time.

Of course, the problem of 24 bit fixed point is its expense: which probably explains why Motorola later produced the cheap, 16 bit DSP56156 - although this looks like a 16 bit variant of the DSP56002:


And of course there has to be a floating point variant - the DSP96002 looks like a floating point version of the DSP56002:


The DSP96002 supports multiprocessing with an additional 'global bus'which can connect to other DSP96002 processors: it also has a new DMA controller with its own bus

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