Datasheet
2010 Microchip Technology Inc. DS70138G-page 39
dsPIC30F3014/4013
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
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 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 Ta bl e 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).
0x0800
0x0863
Start Addr = 0x0800
End Addr = 0x0863
Length = 0x0032 words
Byte
Address
MOV #0x800,W0
MOV W0,XMODSRT ;set modulo start address
MOV #0x863,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 #0x800,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