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Data Operations
16-bit Arithmetic Mode (DSP56300 Only)
2-6
Optimizing DSP56300/DSP56600 Applications
2.2
16-BIT ARITHMETIC MODE (DSP56300 ONLY)
The 16-bit Arithmetic mode causes the Data ALU to use only 16 bits
of the 24-bit data in transfers and calculations, allowing use of the
DSP56300 as a 16-bit data processor. The 16-bit data is right aligned
in the memory, but left aligned in data registers (in order to comply
with the fractional numerical representation convention). The
hardware makes the proper alignments and shifts in data transfers
and operations, so the user does not have any overhead when using
this mode. This includes the accumulators, which in the 16-bit mode
are 40-bits wide (in accumulator A, for example, A0 and A1 are 16
bits each, and the extension A2 remains 8 bits wide). All data
operations are properly defined to give correct 16-bit arithmetic
results. For more information on the 16-bit Arithmetic mode, see
Section 3.4 in the DSP56300 Family Manual for a general
description, and Appendix A in the same manual (Instruction set)
for a detailed description on the functionality of each instruction
affected by this mode.
Using the 16-bit Arithmetic mode may give many advantages from
a general system point of view:
• Ability to implement a 16-bit exact algorithms. The DSP56300
also supports saturation arithmetic and flexible rounding
modes required by some standards.
• 16-bit exact algorithms exact algorithms could be integrated
easily into a software system that also includes 24-bit exact
routines. Changing of the arithmetic mode can be done "on
the fly".
The 16-bit Arithmetic mode is activated by setting the SA bit in the
Status Register (SR).
Note: This is not the same as the 16-bit Compatibility mode
(activated by setting the SC bit in the Status Register). The
16-bit Compatibility mode affects address registers and
address calculations and enables object code compatibility
with the DSP56000 family (which uses 16-bit wide
addresses).
MOTOROLA
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