DSPIC30F2011 Datasheet, PDF (45/207 Pages) Microchip Technology – High-Performance Digital Signal Controllers

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).
Note:
Y space modulo addressing EA calcula-
tions assume word sized data (LS bit of
every EA is always clear).
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 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
Byte
Address
0x1100
0x1163
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
AGAIN: INC W0,W0 ;increment the fill value
Start Addr = 0x1100
End Addr = 0x1163
Length = 0x0032 words
© 2005 Microchip Technology Inc.
Preliminary
DS70139C-page 43