dsPIC30F2011 datasheet(44/206 Pages) MICROCHIP

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dsPIC30F2011/2012/3012/3013

DS70139F-page 44

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

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

4.1.4

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 belong

to the set {W8, W9, W10, W11}. For data reads, W8

and W9 are always directed to the X RAGU. W10 and

W11 are always 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)

4.1.5

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

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 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),

end

address

(for decrementing buffers) based upon the direction of

the buffer.

The only exception to the usage restrictions is for

buffers that have a power-of-2 length. As these buffers

satisfy the Start and the end address criteria, they can

operate in a Bidirectional mode (i.e., address boundary

checks are performed on both the lower and upper

address boundaries).

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:

addressing is only available for W9 (in X

space) and W11 (in Y space).

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