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© 2004 Microchip Technology Incorporated. All Rights Reserved. Introduction to the dsPIC30F Architecture (Part 2) 13
DSP Features
l All DSP operations execute in a single cycle
l Single-cycle Multiply-Accumulate (MAC) instruction:
l Dual Address Generator Units (AGU) support parallel
operand (data and coefficient) fetches
l Accumulator write-back
l 17 x 17-bit Fractional/Integer Multiplier
l Supports mixed-sign operations
l Two 40 bit Accumulators
l Useful for complex arithmetic and multiple filters
l Overflow detection for accumulator values
l Multiple accumulator data saturation modes
Being a Digital Signal Controller, the dsPIC30F provides substantial DSP functionality to
facilitate the efficient implementation of signal processing algorithms such as signal
filtering or frequency spectrum analysis, or other such mathematically intensive tasks.
Speed of execution is especially crucial for real-time applications, for example,
processing of audio signals, because typically one needs to complete a set of
computations on the current data before the next data set is sampled. This necessitates
the presence of specialized on-chip hardware functionality that speeds up mathematical
operations such as multiplication or division of fractional data. The dsPIC30F
architecture provides a cost-effective solution for these DSP-oriented requirements.
Most instructions execute in a single cycle on the dsPIC30F. This is also true for
fundamental DSP operations like Multiply-Accumulate, or MAC. Moreover, the dual
Address Generation Units, or AGUs, on the dsPIC30F ensure that both source
operands of a multiplication operation can be prefetched simultaneously, thereby
speeding up repetitive MAC operations. Two 40-bit accumulators are provided to store
the temporary results of such calculations, for example, in a digital filter. One of the
main benefits of having 2 accumulators is the ability to perform complex-valued
computations, with 1 accumulator being used for the real part ofa calculation and the
other one for the imaginary part. At the same time, the value of the other accumulator
can be stored back in a W register or RAM location using a feature called Accumulator
Write-Back. The dsPIC30F supports a rich set of single cycle DSP instructions
The dsPIC30F also supports automatic overflow detection and saturation of data, which
is very useful in preventing or correcting data overflows that may result from repetitive
accumulation of multiplication results. There is also a 17x17-bit multiplier that can be
used for multiplying both fractional and integer values, and which also allows mixed-
sign multiplication.
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