General Operation

For all operations, the resulting 40-bit product is extended to a 48-bit value (using sign-extension for signed integer and fractional operands, zero-fill for unsigned integer operands) before being combined with the 48-bit destination accumulator.

Figure 3-4and Figure 3-5show relative alignment of input operands, the full 64-bit product, the resulting 40-bit product used for accumulation, and 48-bit accumulator formats.

Product

Extended Product

+

Accumulator

 

OperandY

 

32

X

OperandX

 

32

 

 

 

 

 

40

23

 

 

840

8 40

“0”

8

Extension Byte Upper [7:0]

Accumulator [31:0]

Extension Byte Lower [7:0]

Figure 3-4. Fractional Alignment

OperandY

XOperandX

32

32

Product

Extended Product

+

Accumulator

24

 

8

32

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8

8

32

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8

8

32

Extension Byte Upper [7:0]

 

 

Accumulator

 

[31:0]

 

 

 

 

 

 

Extension Byte Lower [7:0]

Figure 3-5. Signed and Unsigned Integer Alignment

3-4

MCF5282 User’s Manual

MOTOROLA

Page 108
Image 108
Motorola MCF5282, MCF5281 user manual Fractional Alignment