DSPIC30F6014 datasheet(34/222 Pages) MICROCHIP

34 / 222 page

dsPIC30F6011/6012/6013/6014

DS70117C-page 32

Preliminary

 2004 Microchip Technology Inc.

FIGURE 3-9:

DATA SPACE FOR MCU AND DSP (MAC CLASS) INSTRUCTIONS EXAMPLE

TABLE 3-2:

EFFECT OF INVALID

MEMORY ACCESSES

All effective addresses are 16 bits wide and point to

bytes within the data space. Therefore, the data space

address range is 64 Kbytes or 32K words.

3.2.3

DATA SPACE WIDTH

The core data width is 16 bits. All internal registers are

organized as 16-bit wide words. Data space memory is

organized in byte addressable, 16-bit wide blocks.

3.2.4

DATA ALIGNMENT

help

maintain

backward

compatibility

with

PICmicro® devices and improve data space memory

usage efficiency, the dsPIC30F instruction set supports

both word and byte operations. Data is aligned in data

memory and registers as words, but all data space EAs

resolve to bytes. Data byte reads will read the complete

word which contains the byte, using the LS bit of any

EA to determine which byte to select. The selected byte

is placed onto the LS Byte of the X data path (no byte

accesses are possible from the Y data path as the MAC

class of instruction can only fetch words). That is, data

memory and registers are organized as two parallel

byte wide entities with shared (word) address decode

but separate write lines. Data byte writes only write to

the corresponding side of the array or register which

matches the byte address.

As a consequence of this byte accessibility, all effective

address calculations (including those generated by the

DSP operations which are restricted to word sized

data) are internally scaled to step through word aligned

memory. For example, the core would recognize that

Post-Modified Register Indirect Addressing mode

[Ws++] will result in a value of Ws+1 for byte operations

and Ws+2 for word operations.

SFR SPACE

(Y SPACE)

SFR SPACE

UNUSED

Y SPACE

UNUSED

Non-MAC Class Ops (Read)

MAC

Class Ops (Read)

Indirect EA from any W

Indirect EA from W8, W9

Indirect EA from W10, W11

Attempted Operation

Data Returned

EA = an unimplemented address

0x0000

W8 or W9 used to access Y data

space in a MAC instruction

0x0000

W10 or W11 used to access X

data space in a MAC instruction

0x0000

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