AVR Hardware Design

Minimum system:

A resonant circuit consisting of quartz crystals and capacitors is used in the ATMEGA16 pin XTAL1 and XTAL2 Sisu, and the oscillator source of the OSC (oscillator) oscillator circuit in the chip is used as the system clock source. A simpler circuit is to use the 4M RC oscillator directly on the chip, so that the C1, C2, R2 and 4M crystals can be omitted, the pins XTAL1 and XTAL2 floating, of course, the system clock frequency accuracy than the use of external crystals, but also susceptible to temperature changes.

The reset source and reset mode of AVR:

The reset is the microcontroller chip itself hardware initialization operation, for example, the microcontroller in the power on when the need to reset, so that the CPU and other internal functional components are in a certain initial state, and from this initial state to work.

AVR MCU reset operation, the main function is to initialize the program counter PC to $0000 (refers to the non-boot load mode start), so that the microcontroller from the $0000 unit to execute the program. At the same time, the majority of registers (general-purpose registers and I/O registers) are also zeroed by the reset operation.

There are 5 reset sources for the ATMEGA16 microcontroller, which are:

1, power-on reset. When the system supply voltage is lower than the power-on reset threshold Vpot, the MCU resets.

2, external reset. When the external pin reset is low and the low duration is longer than 1.5us, the MCU resets.
3, the power-down detection (BOD) reset. When the BOD is enabled and the supply voltage is lower than the reset threshold (4.0v or 2.7v) of the power-down detection, the MCU resets.
4, watchdog reset. When WDT is enabled and the WDT timeout overflows, the MCU resets.
5, JTAG AVR reset. When using the Jtag interface, the MCU can be reset by the JTAG port control.

AVR Hardware Design