DSPIC33EP128GS708 datasheet(60/484 Pages) MICROCHIP

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dsPIC33EPXXXGS70X/80X FAMILY

DS70005258C-page 60

 2016-2018 Microchip Technology Inc.

4.9

Interfacing Program and Data

Memory Spaces

The dsPIC33EPXXXGS70X/80X family architecture

uses a 24-bit wide Program Space (PS) and a 16-bit

wide Data Space (DS). The architecture is also a

modified Harvard scheme, meaning that data can also

be present in the Program Space. To use this data

successfully, it must be accessed in a way that preserves

the alignment of information in both spaces.

Aside from normal execution, the architecture of the

dsPIC33EPXXXGS70X/80X family devices provides

two methods by which Program Space can be

accessed during operation:

• Using table instructions to access individual bytes

or words anywhere in the Program Space

• Remapping a portion of the Program Space into

the Data Space (Program Space Visibility)

Table instructions allow an application to read or write

to small areas of the program memory. This capability

makes the method ideal for accessing data tables that

need to be updated periodically. It also allows access

to all bytes of the program word. The remapping

method allows an application to access a large block of

data on a read-only basis, which is ideal for look-ups

from a large table of static data. The application can

only access the least significant word of the program

word.

TABLE 4-19:

PROGRAM SPACE ADDRESS CONSTRUCTION

FIGURE 4-12:

DATA ACCESS FROM PROGRAM SPACE ADDRESS GENERATION

Access Type

Access

Space

Program Space Address

<23>

<22:16>

<15>

<14:1>

<0>

Instruction Access

(Code Execution)

User

PC<22:1>

0xxx xxxx xxxx xxxx xxxx xxx0

TBLRD/TBLWT

(Byte/Word Read/Write)

User

TBLPAG<7:0>

Data EA<15:0>

0xxx xxxx

xxxx xxxx xxxx xxxx

Configuration

TBLPAG<7:0>

Data EA<15:0>

1xxx xxxx

xxxx xxxx xxxx xxxx

Program Counter

23 Bits

Program Counter(1)

TBLPAG

8 Bits

16 Bits

Byte Select

1/0

User/Configuration

Table Operations(2)

Space Select

24 Bits

1/0

Note 1:

The Least Significant bit (LSb) of Program Space addresses is always fixed as ‘0’ to maintain

word alignment of data in the Program and Data Spaces.

Table operations are not required to be word-aligned. Table Read operations are permitted in the

configuration memory space.

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