参数资料
型号: ATMEGA644P-B15AZ
厂商: Atmel
文件页数: 14/70页
文件大小: 0K
描述: IC MCU 8BIT 64KB FLASH 44TQFP
标准包装: 1,500
系列: AVR® ATmega
核心处理器: AVR
芯体尺寸: 8-位
速度: 16MHz
连通性: I²C,SPI,UART/USART
外围设备: 欠压检测/复位,POR,PWM,WDT
输入/输出数: 32
程序存储器容量: 64KB(32K x 16)
程序存储器类型: 闪存
EEPROM 大小: 2K x 8
RAM 容量: 4K x 8
电压 - 电源 (Vcc/Vdd): 2.7 V ~ 5.5 V
数据转换器: A/D 8x10b
振荡器型: 内部
工作温度: -40°C ~ 125°C
封装/外壳: 44-TQFP
包装: 带卷 (TR)
21
7674F–AVR–09/09
ATmega164P/324P/644P
6.4
EEPROM Data Memory
The ATmega164P/324P/644P contains 512B/1K/2K bytes of data EEPROM memory. It is orga-
nized 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.
For a detailed description of SPI, JTAG and Parallel data downloading to the EEPROM, see
page 311, page 315, and page 300 respectively.
6.4.1
EEPROM Read/Write Access
The EEPROM Access Registers are accessible in the I/O space. See “Register Description” on
page 23 for details.
The write access time for the EEPROM is given in Table 6-2 on page 25. A self-timing function,
however, lets the user software detect when the next byte can be written. If the user code con-
tains instructions that write the EEPROM, some precautions must be taken. In heavily filtered
power supplies, V
CC 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. See “Preventing EEPROM Corruption” on page 21. for details on how to avoid problems in
these situations.
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
executed. When the EEPROM is written, the CPU is halted for two clock cycles before the next
instruction is executed.
6.4.2
Preventing EEPROM Corruption
During periods of low V
CC, the EEPROM data can be corrupted because the supply voltage is
too low for the CPU and the EEPROM to operate properly. These issues are the same as for
board level systems using EEPROM, and the same design solutions should be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too low. First,
a regular write sequence to the EEPROM requires a minimum voltage to operate correctly. Sec-
ondly, the CPU itself can execute instructions incorrectly, if the supply voltage is too low.
EEPROM data corruption can easily be avoided by following this design recommendation:
Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can
be done by enabling the internal Brown-out Detector (BOD). If the detection level of the internal
BOD does not match the needed detection level, an external low V
CC reset Protection circuit can
be used. If a reset occurs while a write operation is in progress, the write operation will be com-
pleted provided that the power supply voltage is sufficient.
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