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ATMEGA64A-AU 参数 Datasheet PDF下载

ATMEGA64A-AU图片预览
型号: ATMEGA64A-AU
PDF下载: 下载PDF文件 查看货源
内容描述: 8位微控制器,带有64K字节的系统内可编程闪存 [8-bit Microcontroller with 64K Bytes In-System Programmable Flash]
分类和应用: 闪存微控制器
文件页数/大小: 392 页 / 7964 K
品牌: ATMEL [ ATMEL ]
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ATmega64A  
10. System Control and Reset  
10.0.1  
Resetting the AVR  
During Reset, all I/O Registers are set to their initial values, and the program starts execution  
from the Reset Vector. The instruction placed at the Reset Vector must be a JMP – absolute  
jump – instruction to the Reset handling routine. If the program never enables an interrupt  
source, the Interrupt Vectors are not used, and regular program code can be placed at these  
locations. This is also the case if the Reset Vector is in the Application section while the Interrupt  
Vectors are in the Boot section or vice versa. The circuit diagram in Figure 10-1 shows the Reset  
logic. Table 28-3 defines the electrical parameters of the Reset circuitry.  
The I/O ports of the AVR are immediately Reset to their initial state when a reset source goes  
active. This does not require any clock source to be running.  
After all reset sources have gone inactive, a delay counter is invoked, stretching the Internal  
Reset. This allows the power to reach a stable level before normal operation starts. The Time-  
out period of the delay counter is defined by the user through the CKSEL Fuses. The different  
selections for the delay period are presented in “Clock Sources” on page 38.  
10.0.2  
Reset Sources  
The ATmega64A has five sources of reset:  
• Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset  
threshold (VPOT).  
• External Reset. The MCU is reset when a low level is present on the RESET pin for longer  
than the minimum pulse length.  
• Watchdog Reset. The MCU is reset when the Watchdog Timer period expires and the  
Watchdog is enabled.  
• Brown-out Reset. The MCU is reset when the supply voltage VCC is below the Brown-out  
Reset threshold (VBOT) and the Brown-out Detector is enabled.  
• JTAG AVR Reset. The MCU is reset as long as there is a logic one in the Reset Register, one  
of the scan chains of the JTAG system. Refer to the section “IEEE 1149.1 (JTAG) Boundary-  
scan” on page 259 for details.  
51  
8160C–AVR–07/09  
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