DSPIC30F3010_13 Datasheet, PDF (40/228 Pages) Microchip Technology – High-Performance,16-Bit Digital Signal Controllers

dsPIC30F3010/3011
4.1.3
MOVE AND ACCUMULATOR
INSTRUCTIONS
Move instructions and the DSP Accumulator class of
instructions provide a greater degree of addressing
flexibility than other instructions. In addition to the
addressing modes supported by most MCU instruc-
tions, move and accumulator instructions also support
Register Indirect with Register Offset Addressing
mode, also referred to as Register Indexed mode.
Note:
For the MOV instructions, the addressing
mode specified in the instruction can differ
for the source and destination EA. How-
ever, the 4-bit Wb (Register Offset) field is
shared between both source and
destination (but typically only used by
one).
In summary, the following addressing modes are
supported by move and accumulator instructions:
• Register Direct
• Register Indirect
• Register Indirect Post-Modified
• Register Indirect Pre-Modified
• Register Indirect with Register Offset (Indexed)
• Register Indirect with Literal Offset
• 8-bit Literal
• 16-bit Literal
Note:
Not all instructions support all the
addressing modes given above. Individual
instructions may support different subsets
of these addressing modes.
4.1.4 MAC INSTRUCTIONS
The dual source operand DSP instructions (CLR, ED,
EDAC, MAC, MPY, MPY.N, MOVSAC and MSC), also
referred to as MAC instructions, utilize a simplified set of
addressing modes to allow the user to effectively
manipulate the Data Pointers through register indirect
tables.
The two source operand prefetch registers must be a
member of the set {W8, W9, W10, W11}. For data
reads, W8 and W9 will always be directed to the X
RAGU and W10 and W11 will always be directed to the
Y AGU. The effective addresses generated (before and
after modification) must, therefore, be valid addresses
within X data space for W8 and W9 and Y data space
for W10 and W11.
Note:
Register Indirect with Register Offset
Addressing is only available for W9 (in X
space) and W11 (in Y space).
In summary, the following addressing modes are
supported by the MAC class of instructions:
• Register Indirect
• Register Indirect Post-Modified by 2
• Register Indirect Post-Modified by 4
• Register Indirect Post-Modified by 6
• Register Indirect with Register Offset (Indexed)
4.1.5 OTHER INSTRUCTIONS
Besides the various addressing modes outlined above,
some instructions use literal constants of various sizes.
For example, BRA (branch) instructions use 16-bit
signed literals to specify the branch destination directly,
whereas the DISI instruction uses a 14-bit unsigned
literal field. In some instructions, such as ADD Acc, the
source of an operand or result is implied by the opcode
itself. Certain operations, such as NOP, do not have any
operands.
4.2 Modulo Addressing
Modulo Addressing is a method of providing an auto-
mated means to support circular data buffers using
hardware. The objective is to remove the need for soft-
ware to perform data address boundary checks when
executing tightly looped code, as is typical in many
DSP algorithms.
Modulo Addressing can operate in either data or
program space (since the Data Pointer mechanism is
essentially the same for both). One circular buffer can be
supported in each of the X (which also provides the
pointers into program space) and Y data spaces. Modulo
Addressing can operate on any W register pointer.
However, it is not advisable to use W14 or W15 for
Modulo Addressing, since these two registers are used
as the Stack Frame Pointer and Stack Pointer,
respectively.
In general, any particular circular buffer can only be
configured to operate in one direction, as there are
certain restrictions on the buffer start address (for
incrementing buffers) or end address (for decrementing
buffers) based upon the direction of the buffer.
The only exception to the usage restrictions is for
buffers which have a power-of-2 length. As these
buffers satisfy the start and end address criteria, they
may operate in a Bidirectional mode, (i.e., address
boundary checks will be performed on both the lower
and upper address boundaries).
DS70141F-page 40
© 2010 Microchip Technology Inc.