PROGRAMMING MODEL
MOTOROLA
PROGRAM CONTROL UNIT
5 - 11
5.4.2.6
Extension (Bit 5)
The extension (E) bit is cleared if all the bits of the integer portion of the 56-bit result are
all ones or all zeros; otherwise, this bit is set. The integer portion, defined by the scaling
mode and the E bit, is computed as follows:
If the E bit is cleared, then the low-order fraction portion contains all the significant bits;
the high-order integer portion is just sign extension. In this case, the accumulator exten-
sion register can be ignored. If the E bit is set, it indicates that the accumulator extension
register is in use.
5.4.2.7
Limit (Bit 6)
The limit (L) bit is set if the overflow bit is set. The L bit is also set if the data shifter/limiter
circuits perform a limiting operation; otherwise, it is not affected. The L bit is cleared only
by a processor reset or by an instruction that specifically clears it, which allows the L bit
to be used as a latching overflow bit (i.e., a “sticky” bit). L is affected by data movement
operations that read the A or B accumulator registers.
5.4.2.8
Scaling Bit (Bit 7)
The scaling bit (S) is used to detect data growth, which is required in Block Floating Point
FFT operation. Typically, the bit is tested after each pass of a radix 2 FFT and, if it is set,
the scaling mode should be activated in the next pass. The Block Floating Point FFT al-
gorithm is described in the Motorola application note APR4/D, “Implementation of Fast
Fourier Transforms on Motorola’s DSP56000/DSP56001 and DSP96002 Digital Signal
Processors.” This bit is computed according to the following logical equations when the
result of accumulator A or B is moved to XDB or YDB. It is a “sticky” bit, cleared only by
an instruction that specifically clears it.
S1
S0
Scaling Mode
Integer Portion
0
0
No Scaling
Bits 55,54........48,47
0
1
Scale Down
Bits 55,54........49,48
1
0
Scale Up
Bits 55,54........47,46
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 ...