PIC24FJ64GA310 datasheet(67/406 Pages) MICROCHIP

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DS39996F-page 67

PIC24FJ128GA310 FAMILY

4.2.5.2

Data Write into EDS

In order to write data to EDS space, such as in EDS

reads, an Address Pointer is set up by loading the

required EDS page number into the DSWPAG register,

and assigning the offset address to one of the W regis-

ters. Once the above assignment is done, then the

EDS window is enabled by setting bit 15 of the working

accessed location can be written.

Figure 4-2 illustrates how the EDS space address is

generated for write operations.

When the MSBs of EA are ‘1’, the lower 9 bits of

DSWPAG are concatenated to the lower 15 bits of EA

to form a 24-bit EDS address for write operations.

Example 4-2 shows how to write a byte, word and

double-word to EDS.

The Page registers (DSRPAG/DSWPAG) do not

update automatically while crossing a page boundary,

when the rollover happens from 0xFFFF to 0x8000.

While developing code in assembly, care must be taken

to update the page registers when an Address Pointer

crosses the page boundary. The ‘C’ compiler keeps

track of the addressing, and increments or decrements

the Page registers accordingly while accessing

contiguous data memory locations.

FIGURE 4-6:

EDS ADDRESS GENERATION FOR WRITE OPERATIONS

EXAMPLE 4-2:

EDS WRITE CODE IN ASSEMBLY

Note 1:

All write operations to EDS are executed

in a single cycle.

Use of Read/Modify/Write operation on

any EDS location under a REPEAT

instruction is not supported. For example,

BCLR, BSW, BTG, RLC f, RLNC f,

RRC f, RRNC f, ADD f,

SUB

SUBR f, AND f, IOR f,

XOR

ASR f, ASL f

Use

the

DSRPAG

while

performing Read/Modify/Write operations.

DSWPAG Reg

Select

15 Bits

9 Bits

24-Bit EA

Wn<0> is Byte Select

; Set the EDS page where the data to be written

mov

#0x0002 , w0

mov

w0 , DSWPAG

;page 2 is selected for write

mov

#0x0800 ,

;select the location (0x800) to be written

bset

w1 , #15

;set the MSB of the base address, enable EDS mode

;Write a byte to the selected location

mov

#0x00A5 , w2

mov

#0x003C , w3

mov.b

w2 , [w1++]

;write Low byte

mov.b

w3 , [w1++]

;write High byte

;Write a word to the selected location

mov

#0x1234

, w2

;

mov

w2 , [w1]

;

;Write a Double - word to the selected location

mov

#0x1122 , w2

mov

#0x4455 , w3

mov.d

w2 , [w1]

;2 EDS writes

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