Analog Devices ADSP-21261 SHARC Hardware Reference Manual page 84

Multiply Accumulator (Multiplier)
In addition to multiplication, fixed-point operations include accumula-
tion, rounding, and saturation of fixed-point data. There are three
register operations: clear (
The operation (
Clr
it is best to perform this operation at the start of a multiply/accumulate
operation to remove results left over from the previous operation.
The operation (
Rnd
ger results are not effected. This operation rounds the 80-bit
nearest at bit 32; for example, the
fixed-point result occurs either as part of a multiply or multiply/accumu-
late operation or as an explicit operation on the
result in can be sent either to the register file or back to the same
MRF1
register. To round a fractional result to zero (truncation) instead of to
nearest, a program transfers the unrounded result from
the lower 32 bits in
The operation (
Sat
value has overflowed. Overflow occurs when the
the maximum value for the data format—unsigned or twos-complement
and integer or fractional—as specified in the saturate instruction. The six
possible maximum values appear in
tion can be sent either to the register file or back to the same
Table 2-6. Fixed-Point Format Maximum Values (For
Saturation)
Maximum Number
Two's-complement fractional (positive)
Two's-complement fractional (negative)
Two's-complement integer (positive)
Two's-complement integer (negative)
2-26
), round (
Clr
=0) resets the specified
MRF
) applies only to fractional results, so inte-
MRF=Rnd MRF
MRF1
.
MRF0
) sets
MRF=Sat MRF
Table
(Hexadecimal)
MRF2
0000
FFFF
0000
FFFF
ADSP-2126x SHARC Processor Hardware Reference
), and saturate (
Rnd
register to zero. Often,
MRF
- boundary. Rounding of a
MRF0
register. The rounded
MRF
MRF1
to a maximum value if the
MRF
value is greater than
MRF
2-6. The result from
MRF1
7FFF FFFF
8000 0000
0000 0000
FFFF FFFF
MRF
).
Sat
value to
MRF
MRF
, discarding
MRF
satura-
MRF
register.
MRF
MRF0
FFFF FFFF
0000 0000
7FFF FFFF
8000 0000