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I2CCON 数据表(PDF) 45 Page - Microchip Technology |
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I2CCON 数据表(HTML) 45 Page - Microchip Technology |
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45 / 210 page ![]() © 2010 Microchip Technology Inc. DS70139G-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 register, 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 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 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 DO 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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