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ATmega128-16AU データシート(PDF) 35 Page - ATMEL Corporation |
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ATmega128-16AU データシート(HTML) 35 Page - ATMEL Corporation |
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35 / 386 page  35 2467S–AVR–07/09 ATmega128 Using all 64KB Locations of External Memory Since the External Memory is mapped after the Internal Memory as shown in Figure 11, only 60KB of External Memory is available by default (address space 0x0000 to 0x10FF is reserved for internal memory). However, it is possible to take advantage of the entire External Memory by masking the higher address bits to zero. This can be done by using the XMMn bits and control by software the most significant bits of the address. By setting Port C to output 0x00, and releas- ing the most significant bits for normal Port Pin operation, the Memory Interface will address 0x0000 - 0x1FFF. See the following code examples. Note: 1. See “About Code Examples” on page 9. Care must be exercised using this option as most of the memory is masked away. Assembly Code Example (1) ; OFFSET is defined to 0x2000 to ensure ; external memory access ; Configure Port C (address high byte) to ; output 0x00 when the pins are released ; for normal Port Pin operation ldi r16, 0xFF out DDRC, r16 ldi r16, 0x00 out PORTC, r16 ; release PC7:5 ldi r16, (1<<XMM1)|(1<<XMM0) sts XMCRB, r16 ; write 0xAA to address 0x0001 of external ; memory ldi r16, 0xaa sts 0x0001+OFFSET, r16 ; re-enable PC7:5 for external memory ldi r16, (0<<XMM1)|(0<<XMM0) sts XMCRB, r16 ; store 0x55 to address (OFFSET + 1) of ; external memory ldi r16, 0x55 sts 0x0001+OFFSET, r16 C Code Example (1) #define OFFSET 0x2000 void XRAM_example(void) { unsigned char *p = (unsigned char *) (OFFSET + 1); DDRC = 0xFF; PORTC = 0x00; XMCRB = (1<<XMM1) | (1<<XMM0); *p = 0xaa; XMCRB = 0x00; *p = 0x55; } |
同様の部品番号 - ATmega128-16AU |
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同様の説明 - ATmega128-16AU |
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