DSPIC30F2012 datasheet(45/206 Pages) MICROCHIP

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DS70139F-page 45

dsPIC30F2011/2012/3012/3013

4.2.1

START AND END ADDRESS

The Modulo Addressing scheme requires that a

starting and an ending address be specified and loaded

into the 16-bit Modulo Buffer Address registers:

XMODSRT, XMODEND, YMODSRT and YMODEND

(see Table 3-3).

The length of a circular buffer is not directly specified. It

is determined by the difference between the

corresponding Start and end addresses. The maximum

possible length of the circular buffer is 32K words

(64 Kbytes).

4.2.2

W ADDRESS REGISTER

SELECTION

The Modulo and Bit-Reversed Addressing Control

well as a W register field to specify the W address

registers. The XWM and YWM fields select which

registers

operate

with

Modulo

Addressing.

If XWM = 15, X RAGU and X WAGU Modulo

Addressing is disabled. Similarly, if YWM = 15, Y AGU

Modulo Addressing is disabled.

The X Address Space Pointer W register (XWM), to

which Modulo Addressing is to be applied, is stored in

MODCON<3:0> (see Table 3-3). Modulo Addressing is

enabled for X data space when XWM is set to any value

other than ‘15’ and the XMODEN bit is set at

MODCON<15>.

The Y Address Space Pointer W register (YWM), to

which Modulo Addressing is to be applied, is stored in

MODCON<7:4>. Modulo Addressing is enabled for Y

data space when YWM is set to any value other

than ‘15’

and

the

YMODEN

bit

set

MODCON<14>.

FIGURE 4-1:

MODULO ADDRESSING OPERATION EXAMPLE

Note:

space

Modulo

Addressing

calculations assume word-sized data (LSb

of every EA is always clear).

0x1100

0x1163

Start Addr = 0x1100

End Addr = 0x1163

Length = 0x0032 words

Byte

Address

MOV

#0x1100,W0

MOV

W0,XMODSRT

;set modulo start address

MOV

#0x1163,W0

MOV

W0,MODEND

;set modulo end address

MOV

#0x8001,W0

MOV

W0,MODCON

;enable W1, X AGU for modulo

MOV

#0x0000,W0

;W0 holds buffer fill value

MOV

#0x1110,W1

;point W1 to buffer

AGAIN,#0x31

;fill the 50 buffer locations

MOV

W0,[W1++]

;fill the next location

AGAIN: INC

W0,W0

;increment the fill value

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