PIC24HJ12GP201ESLASHML datasheet(35/234 Pages) MICROCHIP

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Preliminary

DS70282B-page 33

PIC24HJ12GP201/202

3.4

Interfacing Program and Data

Memory Spaces

The PIC24HJ12GP201/202 architecture uses a 24-bit-

wide program space and a 16-bit-wide data space. The

architecture is also a modified Harvard scheme, mean-

ing 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 PIC24HJ12GP201/

202 architecture provides two methods by which pro-

gram 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.

3.4.1

ADDRESSING PROGRAM SPACE

Since the address ranges for the data and program

spaces are 16 and 24 bits, respectively, a method is

needed to create a 23-bit or 24-bit program address

from 16-bit data registers. The solution depends on the

interface method to be used.

For table operations, the 8-bit Table Page register

(TBLPAG) is used to define a 32K word region within

the program space. This is concatenated with a 16-bit

EA to arrive at a full 24-bit program space address. In

this format, the Most Significant bit of TBLPAG is used

to determine if the operation occurs in the user memory

(TBLPAG<7> = 0) or the configuration memory

(TBLPAG<7> = 1).

For remapping operations, the 8-bit Program Space

Visibility register (PSVPAG) is used to define a

16K word page in the program space. When the Most

Significant bit of the EA is ‘1’, PSVPAG is concatenated

with the lower 15 bits of the EA to form a 23-bit program

space address. Unlike table operations, this limits

remapping operations strictly to the user memory area.

Table 3-23 and Figure 3-5 show how the program EA is

created for table operations and remapping accesses

from the data EA. Here, P<23:0> refers to a program

space word, and D<15:0> refers to a data space word.

TABLE 3-23:

PROGRAM SPACE ADDRESS CONSTRUCTION

Access Type

Access

Space

Program Space Address

<23>

<22:16>

<15>

<14:1>

<0>

Instruction Access

(Code Execution)

User

PC<22:1>

0xx

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 Space Visibility

(Block Remap/Read)

User

PSVPAG<7:0>

Data EA<14:0>(1)

xxxx xxxx

xxx xxxx xxxx xxxx

Note 1:

Data EA<15> is always ‘1’ in this case, but is not used in calculating the program space address. Bit 15 of

the address is PSVPAG<0>.

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