section 7 - Index of

S (Scaling Bit)The scaling bit (S) is used to detect data growth, which isrequired in Block Floating Point FFT operation. Typically, the bitis tested after each pass of a radix 2 decimation-in-time FFTand, if it is set, the appropriate scaling mode should be activatedin the next pass. The Block Floating Point FFT algorithm isdescribed in the Motorola application note APR4/D, "Implementationof Fast Fourier Transforms on Motorola's DS P56000/DSP56001 and DSP96002 Digital Signal Processors." This bit iscomputed according to the logical equations below when aninstruction or a parallel move moves the result of accumulator Aor B to XDB or YDB. It is a "sticky" bit, cleared only by an instructionthat specifically clears it.The following logical equations are used to compute the scalingbit based upon the scaling mode bits:If S1 =0 and So=o (no scaling)then S = (A46 XOR A45) OR (B46 XOR B45)If S1 =0 and SO=1 (scale down)then S = (A47 XOR A46) OR (B47 XOR B46)If S1 =1 and SO=O (scale up)then S = (A45 XOR A44) OR (B45 XOR B44)If S1 =1 and SO=1 (reserved)then the S flag is undefined.where Ai and Bi means bit i in accumulator A or B.-L (Limit Bit)E (Extension Bit)Set if the overflow bit V is set or if an instruction or a parallelmove causes the data shifter/limiters to perform a limiting operation.Not affected otherwise. This bit is latched and must bereset by the user.Cleared if all the bits of the signed integer portion of the A or Bresult are the same - i.e., the bit patterns are either 00 ... 00 or11 ... 11. Set otherwise. The signed integer portion is definedby the scaling mode as shown in the following table: