Datasheet

dsPIC33FJXXXGPX06/X08/X10
DS70286C-page 62 © 2009 Microchip Technology Inc.
TABLE 4-35: FUNDAMENTAL ADDRESSING MODES SUPPORTED
4.3.3 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
instructions, move and accumulator instructions also
support Register Indirect with Register Offset
Addressing mode, also referred to as Register Indexed
mode.
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
4.3.4 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 2-source operand prefetch registers must be
members of the set {W8, W9, W10, W11}. For data
reads, W8 and W9 are always 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.
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)
4.3.5 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.
4.4 Modulo Addressing
Modulo Addressing mode is a method of providing an
automated means to support circular data buffers using
hardware. The objective is to remove the need for
software 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
Addressing Mode Description
File Register Direct The address of the file register is specified explicitly.
Register Direct The contents of a register are accessed directly.
Register Indirect The contents of Wn forms the EA.
Register Indirect Post-Modified The contents of Wn forms the EA. Wn is post-modified (incremented or
decremented) by a constant value.
Register Indirect Pre-Modified Wn is pre-modified (incremented or decremented) by a signed constant value
to form the EA.
Register Indirect with Register Offset The sum of Wn and Wb forms the EA.
Register Indirect with Literal Offset The sum of Wn and a literal forms the EA.
Note: For the MOV instructions, the Addressing
mode specified in the instruction can differ
for the source and destination EA.
However, the 4-bit Wb (Register Offset)
field is shared between both source and
destination (but typically only used by
one).
Note: Not all instructions support all the
Addressing modes given above. Individual
instructions may support different subsets
of these Addressing modes.
Note: Register Indirect with Register Offset
Addressing mode is only available for W9
(in X space) and W11 (in Y space).