ATmega48/88/168
Figure 10. Data Memory Map
Data Memory
0x0000 - 0x001F
0x0020 - 0x005F
0x0060 - 0x00FF
32 Registers
64 I/O Registers
160 Ext I/O Reg.
0x0100
Internal SRAM
(512/1024/1024 x 8)
0x02FF/0x04FF/0x04FF
Data Memory Access Times
This section describes the general access timing concepts for internal memory access.
The internal data SRAM access is performed in two clkCPU cycles as described in Figure
11.
Figure 11. On-chip Data SRAM Access Cycles
T1
T2
T3
clkCPU
Address valid
Compute Address
Address
Data
WR
Data
RD
Memory Access Instruction
Next Instruction
EEPROM Data Memory
The ATmega48/88/168 contains 256/512/512 bytes of data EEPROM memory. It is
organized as a separate data space, in which single bytes can be read and written. The
EEPROM has an endurance of at least 100,000 write/erase cycles. The access
between the EEPROM and the CPU is described in the following, specifying the
EEPROM Address Registers, the EEPROM Data Register, and the EEPROM Control
Register.
“Memory Programming” on page 270 contains a detailed description on EEPROM Pro-
gramming in SPI or Parallel Programming mode.
EEPROM Read/Write Access
The EEPROM Access Registers are accessible in the I/O space.
The write access time for the EEPROM is given in Table 3. A self-timing function, how-
ever, lets the user software detect when the next byte can be written. If the user code
contains instructions that write the EEPROM, some precautions must be taken. In
heavily filtered power supplies, VCC is likely to rise or fall slowly on power-up/down. This
causes the device for some period of time to run at a voltage lower than specified as
17
2545D–AVR–07/04
ATMEL [ ATMEL ]
