AT90PWM81(2010) 데이터 시트보기 (PDF) - Atmel Corporation

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AT90PWM81
(Rev.:2010)

8-bit Microcontroller with 8K Bytes In-System Programmable Flash

Atmel Corporation 

Figure 4-3. On-chip Data SRAM Access Cycles

T1

T2

T3

clk

CPU

Address

Data

WR

Data

RD

Compute Address

Address valid

Memory Access Instruction

Next Instruction

4.3 EEPROM Data Memory

The AT90PWM81 contains 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, specify-

ing the EEPROM Address Registers, the EEPROM Data Register, and the EEPROM Control Register.

For a detailed description of SPI and Parallel data downloading to the EEPROM, see “Serial Download-

ing” on page 261, and “Parallel Programming Parameters, Pin Mapping, and Commands” on page 252

respectively.

4.3.1

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 4-2. A self-timing function, however, 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 minimum for the clock frequency used. For details on how to avoid problems in these situa-

tions seeSee “Preventing EEPROM Corruption” on page 25.

In order to prevent unintentional EEPROM writes, a specific write procedure must be followed. Refer to

the description of the EEPROM Control Register for details on this.

When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is exe-

cuted. When the EEPROM is written, the CPU is halted for two clock cycles before the next instruction is

executed.

18 AT90PWM81

7734P–AVR–08/10

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