参数资料
型号: ATMEGA644A-MUR
厂商: Atmel
文件页数: 88/160页
文件大小: 0K
描述: IC MCU AVR 64K FLASH 44VQFN
产品培训模块: MCU Product Line Introduction
megaAVR Introduction
标准包装: 4,000
系列: AVR® ATmega
核心处理器: AVR
芯体尺寸: 8-位
速度: 20MHz
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): 1.8 V ~ 5.5 V
数据转换器: A/D 8x10b
振荡器型: 内部
工作温度: -40°C ~ 85°C
封装/外壳: 44-VFQFN 裸露焊盘
包装: 带卷 (TR)
其它名称: ATMEGA644A-MUR-ND
ATMEGA644A-MURTR
33
8272E–AVR–04/2013
ATmega164A/PA/324A/PA/644A/PA/1284/P
9.3
Low Power Crystal Oscillator
This Crystal Oscillator is a low power oscillator, with reduced voltage swing on the XTAL2 out-
put. It gives the lowest power consumption, but is not capable of driving other clock inputs, and
may be more susceptible to noise in noisy environments. In these cases, refer to the ”Full swing
Some initial guidelines for choosing capacitors for use with crystals are given in Table 9-3. The
crystal should be connected as described in ”Clock source connections” on page 32.
The Low Power Oscillator can operate in three different modes, each optimized for a specific fre-
quency range. The operating mode is selected by the fuses CKSEL3..1 as shown in Table 9-3.
Notes:
1. If the crystal frequency exceeds the specification of the device (depends on VCC), the CKDIV8
Fuse can be programmed in order to divide the internal frequency by 8. It must be ensured
that the resulting divided clock meets the frequency specification of the device.
2. This is the recommended CKSEL settings for the different frequency ranges.
3. This option should not be used with crystals, only with ceramic resonators.
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in Table
Table 9-3.
Low Power Crystal Oscillator Operating Modes
Frequency Range [MHz]
CKSEL3..1 (2)
Recommended Range for Capacitors C1 and C2 [pF]
0.4 - 0.9
100 (3)
0.9 - 3.0
101
12 - 22
3.0 - 8.0
110
12 - 22
8.0 - 16.0
111
12 - 22
Table 9-4.
Start-up Times for the Low Power Crystal Oscillator Clock Selection.
Oscillator source /
power conditions
Start-up time from
power-down and
power-save
Additional delay
from reset
(VCC = 5.0V)
CKSEL0
SUT1..0
Ceramic resonator, fast
rising power
258CK
14CK + 4.1ms(1)
000
Ceramic resonator, slowly
rising power
258CK
14CK + 65ms(1)
001
Ceramic resonator, BOD
enabled
1K CK
14CK(2)
010
Ceramic resonator, fast
rising power
1K CK
14CK + 4.1ms(2)
011
Ceramic resonator, slowly
rising power
1K CK
14CK + 65ms(2)
100
Crystal Oscillator, BOD
enabled
16K CK
14CK
1
01
Crystal Oscillator, fast
rising power
16K CK
14CK + 4.1ms
1
10
Crystal Oscillator, slowly
rising power
16K CK
14CK + 65ms
1
11
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