AT90USB647 datasheet(38/456 Pages) ATMEL

tên linh kiện	AT90USB647

Giải thích chi tiết về linh kiện	135 powerful instructions ??most single clock cycle execution

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7593L–AVR–09/12

AT90USB64/128

Figure 6-10. Address map with 32KB external memory.

6.5.9

Using all 64KB locations of external memory

Since the External Memory is mapped after the Internal Memory as shown in Figure 6-4, only

56KB of External Memory is available by default (address space 0x0000 to 0x20FF 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 - 0x2FFF. See the following code examples.

Care must be exercised using this option as most of the memory is masked away.

0x0000

0x20FF

0xFFFF

0x2100

0x7FFF

0x8000

0x0000

0x7FFF

Memory configuration A

Internal memory

(Unused)

AVR memory map

External 32K SRAM

External

memory

XMem start + 0x8000

ISRAM end + 0x8000

XMem start

ISRAM end

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