DSPIC30F2012AT20ESLASHML datasheet(45/205 Pages) MICROCHIP

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DS70139E-page 43

dsPIC30F2011/2012/3012/3013

4.2.1

START AND END ADDRESS

The Modulo Addressing scheme requires that a start-

ing 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 corre-

sponding Start and end addresses. The maximum pos-

sible length of the circular buffer is 32K words

(64 Kbytes).

4.2.2

W ADDRESS REGISTER

SELECTION

The Modulo and Bit-Reversed Addressing Control reg-

ister, MODCON<15:0>, contains enable flags as well

as a W register field to specify the W address registers.

The XWM and YWM fields select which registers oper-

ate 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 is set at MODCON<14>.

FIGURE 4-1:

MODULO ADDRESSING OPERATION EXAMPLE

Note:

Y space Modulo Addressing EA calcula-

tions 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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