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ATMEGA640 Datasheet(PDF) 314 Page - Microchip Technology |
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ATMEGA640 Datasheet(HTML) 314 Page - Microchip Technology |
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314 / 436 page  314 ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET] DS40002211A 29.5 Addressing the Flash During Self-Programming The Z-pointer is used to address the SPM commands. The Z pointer consists of the Z-registers ZL and ZH in the register file, and RAMPZ in the I/O space. The number of bits actually used is implementation dependent. Note that the RAMPZ register is only implemented when the program space is larger than 64Kbytes. Since the Flash is organized in pages (see Table 30-7 on page 328), the Program Counter can be treated as hav- ing two different sections. One section, consisting of the least significant bits, is addressing the words within a page, while the most significant bits are addressing the pages. This is shown in Figure 29-3. Note that the Page Erase and Page Write operations are addressed independently. Therefore it is of major importance that the Boot Loader software addresses the same page in both the Page Erase and Page Write operation. Once a program- ming operation is initiated, the address is latched and the Z-pointer can be used for other operations. The (E)LPM instruction use the Z-pointer to store the address. Since this instruction addresses the Flash byte-by- byte, also bit Z0 of the Z-pointer is used. Figure 29-3. Addressing the Flash During SPM(1) Note: 1. The different variables used in Figure 29-3 are listed in Table 29-9 on page 320. Bit 23222120 19181716 15 14 13 12 11 10 9 8 RAMPZ RAMPZ7 RAMPZ6 RAMPZ5 RAMPZ4 RAMPZ3 RAMPZ2 RAMPZ1 RAMPZ0 ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8 ZL (R30) Z7 Z6 Z5 Z4 Z3 Z2 Z1 Z0 7 6543 210 PROGRAM MEMORY 0 1 15 Z - REGISTER BIT 0 ZPAGEMSB WORD ADDRESS WITHIN A PAGE PAGE ADDRESS WITHIN THE FLASH ZPCMSB INSTRUCTION WORD PAGE PCWORD[PAGEMSB:0]: 00 01 02 PAGEEND PAGE PCWORD PCPAGE PCMSB PAGEMSB PROGRAM COUNTER |
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