dsp56800e Freescale Semiconductor, Inc, dsp56800e Datasheet - Page 176

• Manufacturer Part Number: dsp56800e
• Description: 16-bit Digital Signal Controller Core
• Manufacturer: Freescale Semiconductor, Inc

Data Arithmetic Logic Unit
The key to making the multiplication work is the use of the MPYSU instruction, as shown in the code in
Example 5-21. Treating the lower half of the 32-bit input value as unsigned ensures that the correct value is
generated for the later addition.
(4 Cycles, 4 Instruction Words)
Extended-precision 32-bit multiplication works similarly. Figure 5-21 on page 5-31 shows two 32-bit
values being multiplied to generate a 64-bit result. The code for this figure appears in Example 5-22 on
page 5-32.
5-30
Example 5-21. Fractional Single-Precision Times Double-Precision—Both Signed
Figure 5-20. Single-Precision-Times-Double-Precision Signed Multiplication
MPYSU
ASR16
MAC
X0,Y0,A
A
X0,Y1,A
Sign Ext.
×
+
A2
DSP56800E Core Reference Manual
Signed × Signed
A1
; Single-Precision times Lower Portion
; 16-bit Arithmetic Right Shift
; Single-Precision times Upper Portion
; and added to Previous
36 Bits
X0 × Y1
Signed × Unsigned
Y1
A0
X0 × Y0
32 Bits
16 Bits
Y0
X0
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