DSPIC30F2012AT20ESLASHML datasheet(44/205 Pages) MICROCHIP

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dsPIC30F2011/2012/3012/3013

DS70139E-page 42

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

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 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 pro-

gram 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. Mod-

ulo Addressing can operate on any W register pointer.

However, it is not advisable to use W14 or W15 for Mod-

ulo Addressing since these two registers are used as

the Stack Frame Pointer and Stack Pointer, respec-

tively.

In general, any particular circular buffer can only be

configured to operate in one direction, as there are cer-

tain restrictions on the buffer Start address (for incre-

menting buffers), or end address (for decrementing

buffers) based upon the direction of the buffer.

The only exception to the usage restrictions is for buff-

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

isfy the Start and 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 address-

ing

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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