ADDRESSING
MOTOROLA
ADDRESS GENERATION UNIT
4 - 23
3. Set Rn between the lower boundary and upper boundary in the buffer mem-
ory. The lower boundary is L x (2
k
), where L is an arbitrary whole number. This
boundary gives a 16-bit binary number “xx . . . xx00 . . . 00”, where xx . . . xx=L
and 00 . . . 00 equals k zeros. The upper boundary is L x (2
k
)+ ((2
k
)–1). This
boundary gives a 16-bit binary number “xx . . . xx11 . . . 11”, where xx . . . xx=L
and 11 . . . 11 equals k ones.
4. Use the (Rn)+ Nn addressing mode.
As an example, consider a 1024-point FFT with real data stored in the X memory and
imaginary data stored in the Y memory. Since 1,024=2
10
, k=10. The modifier register (Mn)
is zero to select bit-reverse addressing. Offset register (Nn) contains the value 512 (2
(k–
1)
), and the pointer register (Rn) contains 3,072 (L x (2
k
)=3 x (2
10
)), which is the lower
boundary of the memory buffer that holds the results of the FFT. The upper boundary is
4,095 (lower bo (2
k
)–1=3,072+ 1,023).
Postincrementing by + N generates the address sequence (0, 512, 256, 768, 128, 640,...),
which is added to the lower boundary. This sequence (0, 512, etc.) is the scrambled FFT
data order for sequential frequency points from 0 to 2
π
. Table 4-3 shows the successive
contents of Rn when using (Rn)+ Nn updates.
The reverse-carry modifier only works when the base address of the FFT data buffer is a
multiple of 2
k
, such as 1,024, 2,048, 3,072, etc. The use of addressing modes other than
postincrement by + Nn is possible but may not provide a useful result.
Rn Contents
Offset From
Lower Boundary
3072
0
3584
512
3328
256
3840
768
3200
128
3712
640
Table 4-3 Bit-Reverse Addressing
Sequence Example
Summary of Contents for DSP56K
Page 12: ...xii LIST of TABLES MOTOROLA List of Tables Continued Table Page Number Title Number ...
Page 13: ...MOTOROLA DSP56K FAMILY INTRODUCTION 1 1 SECTION 1 DSP56K FAMILY INTRODUCTION ...
Page 31: ...MOTOROLA DATA ARITHMETIC LOGIC UNIT 3 1 SECTION 3 DATA ARITHMETIC LOGIC UNIT ...
Page 50: ...DATA ALU SUMMARY 3 20 DATA ARITHMETIC LOGIC UNIT MOTOROLA ...
Page 51: ...MOTOROLA ADDRESS GENERATION UNIT 4 1 SECTION 4 ADDRESS GENERATION UNIT ...
Page 77: ...MOTOROLA PROGRAM CONTROL UNIT 5 1 SECTION 5 PROGRAM CONTROL UNIT ...
Page 124: ...INSTRUCTION GROUPS 6 30 INSTRUCTION SET INTRODUCTION MOTOROLA ...
Page 125: ...MOTOROLA PROCESSING STATES 7 1 SECTION 7 PROCESSING STATES STOP WAIT EXCEPTION NORMAL RESET ...
Page 167: ...STOP PROCESSING STATE MOTOROLA PROCESSING STATES 7 43 ...
Page 168: ...STOP PROCESSING STATE 7 44 PROCESSING STATES MOTOROLA ...
Page 169: ...MOTOROLA PORT A 8 1 SECTION 8 PORT A ...
Page 176: ...PORT A INTERFACE 8 8 PORT A MOTOROLA ...
Page 177: ...MOTOROLA PLL CLOCK OSCILLATOR 9 1 SECTION 9 PLL CLOCK OSCILLATOR x x d Φ VCO ...
Page 191: ...10 2 ON CHIP EMULATION OnCE MOTOROLA SECTION 10 ON CHIP EMULATION OnCE ...
Page 218: ...USING THE OnCE MOTOROLA ON CHIP EMULATION OnCE 10 29 ...
Page 604: ...INSTRUCTION ENCODING A 338 INSTRUCTION SET DETAILS MOTOROLA ...
Page 605: ...MOTOROLA BENCHMARK PROGRAMS B 1 APPENDIX B BENCHMARK PROGRAMS T T T T T P1 P3 P2 P4 T T T ...
Page 609: ...BENCHMARK PROGRAMS MOTOROLA BENCHMARK PROGRAMS B 5 ...
Page 611: ...BENCHMARK PROGRAMS MOTOROLA BENCHMARK PROGRAMS B 7 ...
Page 613: ...BENCHMARK PROGRAMS MOTOROLA BENCHMARK PROGRAMS B 9 ...
Page 615: ...BENCHMARK PROGRAMS MOTOROLA BENCHMARK PROGRAMS B 11 ...