Fuse bit of AVR study notes

Fuse bit of AVR study notes
1. BOD (Brown-out Detection) power-down detection circuit
BODLEVEL (BOD level selection): 1: 2.7V level; 0: 4.0V level.This needs to be selected according to the operating voltage of the chip.

BODEN(BOD function control): 1: BOD function disabled; 0: BOD function enabled

How to use: If BODEN is enabled (check box is selected) to start power-down detection, the detection level is determined by BODLEVEL.Once the VCC drops below the trigger level (2.7v or 4.0v), the MCU resets; when the VCC level is greater than the trigger level, it starts to work again after the tTOUT delay cycle.

2. Reset startup time selection
SUT 1/0: When different crystal oscillators are selected, the SUT is different.If there are no special requirements, it is recommended that SUT 1/0 set the reset startup time to be slightly longer, so that the power supply rises slowly (ie SUT1: 1; SUT0: 0).

3, CKSEL3/2/10: Clock source selection.By default, CKSEL3-0, SUT1 and SYT0 are set to "0001" and "10" respectively, which will use the chip's 8mHz internal crystal oscillator and use the longest startup delay.

Configuration method:

4. M103: Set the ATmega103 compatible mode to work.The factory default setting is 0, which is to run in ATmega103 compatibility mode.

5. JTAGEN: If the JTAG interface is not used, the state of JTAGEN should be set to 1, that is, the JTAG function is disabled, and the JTAG pin is used for the I/O interface.

6, SPIEN: SPI mode download data and program permission, the default state is 0, generally keep its state.

7. WDTON: The watchdog timer is always on.The default is "1", which disables the watchdog timer from always on.Selecting "0" means that the watchdog timer is always on. It is recommended to set it to 0 to prevent the program from running away.

8. EESAVE: When EESAVE is set to "1", it means that when the chip is erased, the data in the flash and EEPROM will be erased together. If set to "0", the erase operation is only valid for the data in the flash.EEPROM is invalid.The factory default setting of the chip is "1".In practical applications, it needs to be set according to actual needs.

9. BOOTRST: Determines the address of the first instruction when it is powered on.The default state is "1", which means that the startup starts from 0x0000; if BOOTRST is set to "0", it starts from the starting position of BOOTLOADER (the first address of BOOTLOADER is determined by BOOTSZ1 and BOOTSZ0).

BOOTSZ1 and BOOTSZ0: These two bits determine the size and starting address of the BOOTLOADER.The default state is "00" for 4096 bytes, starting at 0xF000.

BOOLOADER area size configuration:

Note: inWhen setting the fuse bit, you must first determine whether "√" represents 1 or 0