Datasheet

© 2006 Microchip Technology Inc. DS70117F-page 41
dsPIC30F6011/6012/6013/6014
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, 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
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 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 will
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 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
DO AGAIN,#0x31 ;fill the 50 buffer locations
MOV W0,[W1++] ;fill the next location