ATmega64A datasheet(28/392 Pages) ATMEL

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8160C–AVR–07/09

ATmega64A

0x1100 to 0x90FF. This is illustrated in Figure 7-10. Memory configuration B refers to the

ATmega103 compatibility mode, configuration A to the non-compatible mode.

When the device is set in ATmega103 compatibility mode, the internal address space is 4,096

bytes. This implies that the first 4,096 bytes of the external memory can be accessed at

addresses 0x8000 to 0x8FFF. To the Application software, the external 32 KB memory will

appear as one linear 32 KB address space from 0x1000 to 0x8FFF.

Figure 7-10. Address Map with 32 KB External Memory

7.5.8

Using all 64KB Locations of External Memory

Since the external memory is mapped after the internal memory as shown in Figure 7-4, 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 con-

trolled by software the most significant bits of the address. By setting Port C to output 0x00, and

releasing the most significant bits for normal Port Pin operation, the Memory Interface will

address 0x0000 - 0x1FFF. See code examples below.

0x0000

0x10FF

0xFFFF

0x1100

0x7FFF

0x8000

0x90FF

0x9100

0x0000

0x10FF

0x1100

0x7FFF

Memory Configuration A

Memory Configuration B

Internal Memory

(Unused)

AVR Memory Map

External 32K SRAM

External

Memory

0x0000

0x0FFF

0xFFFF

0x1000

0x7FFF

0x8000

0x8FFF

0x9000

0x0000

0x0FFF

0x1000

0x7FFF

Internal Memory

(Unused)

AVR Memory Map

External 32K SRAM

External

Memory

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