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Fast Fourier Transforms on Motorola's Digital Signal Processors

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The data paths are 24 bits wide, thereby providing<br />

144 dB of dynamic range. More importantly, intermediate<br />

results are held by a 56-bit accumulator which<br />

gives more accuracy in noise sensitive applicati<strong>on</strong>s.<br />

The data ALU, address arithmetic units, and program<br />

c<strong>on</strong>troller operate in parallel so that an instructi<strong>on</strong> prefetch,<br />

a 24x24-bit multiplicati<strong>on</strong>, a 56-bit additi<strong>on</strong>, two<br />

data moves, and two address pointer updates using<br />

<strong>on</strong>e of three types of arithmetic (linear, modulo, or bitreversed)<br />

can be executed in <strong>on</strong>e instructi<strong>on</strong>. Three<br />

<strong>on</strong>-chip peripherals (Serial Communicati<strong>on</strong> Interface,<br />

Synchr<strong>on</strong>ous Serial Interface and Host interface), a<br />

clock generator and seven buses (three address, four<br />

data) make the overall system functi<strong>on</strong>ally complete<br />

and powerful. The architecture of DSP56001 is<br />

shown in Figure 4-2.<br />

A<br />

B<br />

DIT Butterfly DIF Butterfly<br />

W<br />

Figure 4-3 A radix-2 DIT butterfly needing less<br />

instructi<strong>on</strong> cycles than a radix-2 DIF<br />

butterfly<br />

4-8 MOTOROLA<br />

-<br />

A’<br />

A=Ar+jAi W=Wr-jWi B=Br+jBi<br />

T1=Ar+BrWr (MAC)<br />

Ar’=T1+BiWi (MAC)<br />

Br’=2Ar-Ar’ (SUBL)<br />

T2=Ai-BrWi (MAC)<br />

Ai’=T2+BiWr (MAC)<br />

Bi”=2Ai-Ai” (SUBL)<br />

A<br />

A’<br />

W<br />

B’ B - B’<br />

Ar’=Ar+Br (ADD)<br />

T1=Ar-Br (SUB)<br />

Ai’=Ai+Bi (ADD)<br />

T2=Ai-Bi (SUB)<br />

T3=T1Wr (MPY)<br />

Br’=T3+T2Wi (MAC)<br />

T4=T2Wr (MPY)

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