dsp56800 Freescale Semiconductor, Inc, dsp56800 Datasheet - Page 61

• Manufacturer Part Number: dsp56800
• Description: 16-bit Digital Signal Controllers
• Manufacturer: Freescale Semiconductor, Inc

3.3.2
Four types of two’s-complement data formats are supported by the 16-bit DSC core:
The ranges for each of these formats, discussed in the following subsections, apply to all data stored in
memory and to data stored in the data ALU registers. The extension registers associated with the
accumulators allow word growth so that the most positive signed fractional number that can be represented
in an accumulator is approximately 16.0 and the most negative signed fractional number is -16.0 as shown
in Table 3-3. An important factor to consider is that when the accumulator extension registers are in use,
the data contained in the accumulators cannot be stored exactly in memory or other registers. In these cases
the data must be limited to the most positive or most negative number consistent with the size of the
destination and the sign of the accumulator, the MSB of the extension register.
3.3.2.1
In this format the N bit operand is represented using the 1.[N-1] format (1 sign bit, N-1 fractional bits).
Signed fractional numbers lie in the following range:
For words and long-word signed fractions, the most negative number that can be represented is -1.0, whose
internal representation is $8000 and $8000_0000, respectively. The most positive word is $7FFF or 1.0 -
2
3.3.2.2
Unsigned fractional numbers may be thought of as positive only. The unsigned numbers have nearly twice
the magnitude of a signed number with the same number of bits. Unsigned fractional numbers lie in the
following range:
Examples of unsigned fractional numbers are 0.25, 1.25, and 1.999. The binary word is interpreted as
having a binary point after the MSB. The most positive 16-bit unsigned number is $FFFF formulated
as {1.0 + (1.0 - 2
Freescale Semiconductor
-15
, and the most positive long word is $7FFF_FFFF or 1.0 - 2
•
•
•
•
Signed fractional
Unsigned fractional
Signed integer
Unsigned integer
-1.0 ≤ SF ≤ +1.0 - 2
0.0 ≤ UF ≤ 2.0 - 2
Data Formats
1.
mulators cannot be stored exactly in memory or other registers. In these cases the data
must be limited to the most positive or most negative number consistent with the size
of the destination.
Signed Fractional
Unsigned Fractional
Representation
When the accumulator extension registers are in use, the data contained in the accu-
$F E000 0000
$E C000 0000
Hexadecimal
$8 0000 0001
- [N-1]
Table 3-3. Interpretation of 36-bit Data Values (Continued)
)} = 1.99997. The smallest unsigned number is zero ($0000).
1
-[N-1]
-[N-1]
Entire Accumulator
36-Bit Integer in
-34,359,738,367
- 5,368,709,120
Data Arithmetic Logic Unit
- 536,870,912
(decimal)
16-Bit Integer in MSP
Fractional and Integer Data ALU Arithmetic
-31
(Overflows)
(Overflows)
.
(decimal)
- 8,192
Fractional
(decimal)
Value
- 0.25
-16.0
-2.5
3-17