DSPIC33FJ12MC02ESS datasheet(49/284 Pages) MICROCHIP

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Preliminary

DS70265B-page 47

dsPIC33FJ12MC201/202

3.6.2

DATA ACCESS FROM PROGRAM

MEMORY USING TABLE

INSTRUCTIONS

The TBLRDL and TBLWTL instructions offer a direct

method of reading or writing the lower word of any

address within the program space without going

through data space. The TBLRDH and TBLWTH

instructions are the only method to read or write the

upper 8 bits of a program space word as data.

The PC is incremented by two for each successive

24-bit program word. This allows program memory

addresses to directly map to data space addresses.

Program memory can thus be regarded as two 16-bit-

wide word address spaces, residing side by side, each

with the same address range. TBLRDL and TBLWTL

access the space that contains the least significant

data word. TBLRDH and TBLWTH access the space that

contains the upper data byte.

Two table instructions are provided to move byte or

word-sized (16-bit) data to and from program space.

Both function as either byte or word operations.

• TBLRDL (Table Read Low):

- In Word mode, this instruction maps the

lower word of the program space

location (P<15:0>) to a data address

(D<15:0>).

- In Byte mode, either the upper or lower byte

of the lower program word is mapped to the

lower byte of a data address. The upper byte

is selected when Byte Select is ‘1’; the lower

byte is selected when it is ‘0’.

• TBLRDH (Table Read High):

- In Word mode, this instruction maps the entire

upper word of a program address (P<23:16>)

to a data address. Note that D<15:8>, the

‘phantom byte’, will always be ‘0’.

- In Byte mode, this instruction maps the upper

or lower byte of the program word to D<7:0>

of the data address, in the TBLRDL instruc-

tion. The data is always ‘0’ when the upper

‘phantom’ byte is selected (Byte Select = 1).

In a similar fashion, two table instructions, TBLWTH

and TBLWTL, are used to write individual bytes or

words to a program space address. The details of

their operation are explained in Section 4.0 “Flash

Program Memory”.

For all table operations, the area of program memory

space to be accessed is determined by the Table Page

memory space of the device, including user and

configuration spaces. When TBLPAG<7> = 0, the table

page is located in the user memory space. When

TBLPAG<7> = 1, the page is located in configuration

space.

FIGURE 3-8:

ACCESSING PROGRAM MEMORY WITH TABLE INSTRUCTIONS

00000000

‘Phantom’ Byte

TBLRDH.B (Wn<0> = 0)

TBLRDL.W

TBLRDL.B (Wn<0> = 1)

TBLRDL.B (Wn<0> = 0)

TBLPAG

0x000000

0x800000

0x020000

0x030000

Program Space

The address for the table operation is determined by the data EA

within the page defined by the TBLPAG register.

Only read operations are shown; write operations are also valid in

the user memory area.

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