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ATMEGA324P-20MU 其他数据使用手册 - ATMEL（爱特美尔）
制造商:
ATMEL（爱特美尔）
分类:
8位微控制器
封装:
VQFN-44
描述:
ATMEL ATMEGA324P-20MU 微控制器, 8位, 低功率高性能, ATmega, 20 MHz, 32 KB, 2 KB, 44 引脚, VQFN
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ATMEGA324P-20MU数据手册
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AVR505
3
8001C-AVR-06/06
5 EEPROM Programming
In ATmega16/32 EEPROM data programming is done in one atomic operation, in
ATmega164P/324P/644P it is also possible to split the erase and write operations in
two different operations. The typical EEPROM programming times are also reduced
in ATmega164P/324P/644P.
Table 5-1. EEPROM Programming Time.
ATmega16/32 ATmega164P/324P/644P
Number of
Calibrated RC
Oscillator Cycles
Typical
Programming
Time
Number of
Calibrated RC
Oscillator Cycles
Typical
Programming
Time
EEPROM write
from CPU
8448 8.5 ms 26368 3.3 ms
6 External 32 kHz Watch Crystal
When operating the timer/counter from an external 32.768 kHz watch crystal or an
external clock source, external capacitors might be needed to the TOSC1/2 pins
when using ATmega164P/324P/644P, as opposed to ATmega16/32 where the crystal
can be connected directly between the pins. The internal capacitance of
ATmega164P/324P/644P low-frequency oscillator is typically 6pF, but the tracks to
the crystal will add some additional capacitance. Refer to the datasheet for details on
crystal connections.
The low frequency crystal oscillator of the ATmega164P/324P/644P is optimized for
very low power consumption and thus the crystal driver strength is reduced compared
to the ATmega16/32. This means that when selecting a crystal, its load capacitance
and Equivalent Series Resistance (ESR) must be taken into consideration. Both
values are specified by the crystal vendor.
Table 6-1 shows the ESR
recommendations for ATmega164P/324P/644P.
Table 6-1. ESR recommendation 32.768 kHz crystals with ATmega164P/324P/644P.
Crystal CL [pF] Max ESR [kΩ]
1
6.5 75
9 65
12.5 30
Note: 1. The values stated are for an oscillator allowance safety margin of 5. Since the
oscillator’s transconductance is temperature compensated one can use a safety
margin of 4, thus giving a max ESR of 90, 80 and 40 kΩ respectively.
For examples of crystals that comply with the requirements see
Appendix A.
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