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4.2.5.2

Data Write into EDS

In order to write data to EDS, 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 registers. Once the

above assignment is done, then the EDS window is

enabled by setting bit 15 of the Working register,

assigned with the offset address, and the accessed

location can be written.

Figure 4-5 illustrates how the EDS address is generated

for write operations.

When the MSbs of EA are ‘1’, the lower nine 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 Data Space 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 Data Space 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 4-5:

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.

2: 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 f, SUBR f, AND f,

IOR f, XOR f, ASR f, ASL f.

3: 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, w1

;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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