Table of Contents
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AVR ATmega 328/328p Fuses
If you encounter errors see Errors from AVRdude
For all fuses
| Fuse state | Description |
|---|---|
| 1 | Unprogrammed |
| 0 | Programmed |
Find your programmer
nonexistent is just a variable to make the command generate output
avrdude -c nonexistent
This produces a list of all the programmers supported by avrdude so you can see if you have one and if so what its name is for avrdude
See avrdude for reading flash and eeprom
Arduino UNO Default fuse settings
First the default Atmel AVR factory fusesettings
| L | FF | 0110 0010 |
| H | D9 | 1101 1001 |
| E | FF | 1111 1111 |
From the boards.txt file found in the Arduino IDE version 1.8.9
| L | FF | 1111 1111 | uno.bootloader.low_fuses |
| H | DE | 1101 1110 | uno.bootloader.high_fuses |
| E | FD | 1111 1101 | uno.bootloader.extended_fuses |
So far we found three different default fuse settings
Fresh ATmega328P-PU from China. (On a ZIF USB-B prototyping board with 2 3mm LED's and probably the Arduino Optiboot bootloader)
| L | FF | 1111 1111 |
| H | DE | 1101 1110 |
| E | FD | 1111 1101 |
From Arduino default fuse settings on coding with Cody
| L | FF | 1111 1111 |
| H | DE | 1101 1110 |
| E | 05 | 0000 0101 |
From Arduino atmega 328p fuse settings on Martyn Currey
| L | 62 | 0110 0010 |
| H | D9 | 1101 1001 |
| E | FF | 1111 1111 |
Read fuses
These three commands will read all three fuse blocks. Only the fuse block specified will be written to the specified file
Send the fuseseeting to a file ( - is stdout )
low fuses
avrdude -c usbasp -p m328p -P USB -b 57600 -U lfuse:r:/tmp/extendedfuses.txt:i -v
high fuses
avrdude -c usbasp -p m328p -P USB -b 57600 -U hfuse:r:/tmp/highfuses.txt:i -v
extended fuses
avrdude -c usbasp -p m328p -P USB -b 57600 -U efuse:r:/tmp/extendedfuses.txt:i
Reset the fuses
See:
| AVR High voltage programming Fuses rescue | Fuse settings output after flashing the hex code with avrdude -c usbasp -p m8 -P USB -b 57600 -U flash:w:Rescue.hex: avrdude: safemode: Fuses OK (E:FF, H:D9, L:E1) |
| AVR rescue | |
| ArduinoISP reading writing fuses on the ATmega328P |
Set the fuses
Warning
Setting some specific fuses will cause ISP to be disabled because SPI programming will be disabled. So take care when you want to
- Disable the reset pin
- Enable debugWIRE
You will need one of
- High Voltage (HV) programmer
- Parallel programmer
- A programmer with debugWIRE
to reset and change back those fuses
Low byte fuses
These set the clock
| Name | Bit | Description | Default Value | Remark |
|---|---|---|---|---|
| CKDIV8 | 7 | Divide clock by 8 | 0 | Change to 1 for Arduino |
| CKOUT | 6 | Clock output | 1 | Clock is also on the CLKO pin. This is the system clock |
| SUT1 | 5 | Select start-up time | 1 | |
| SUT0 | 4 | Select start-up time | 0 | Change to 1 for Arduino |
| CKSEL3 | 3 | Select clock source | 0 | Change to 1 for Arduino |
| CKSEL2 | 2 | Select clock source | 0 | Change to 1 for Arduino |
| CKSEL1 | 1 | Select clock source | 1 | |
| CKSEL0 | 0 | Select clock source | 0 | Change to 1 for Arduino |
The default value of the low fusebyte is 0110 0010 being 0x62 in hex
For Arduino we need 1111 1111 being 0xFF in hex
For Arduino without bootloader we need 1111 1111 being 0xFF in hex
CKSEL3..1 = 111 means:
| Frequency Range (MHz) | 8.0 - 16.0 |
| Recommended Range for Capacitors C1 and C2 (pF) | 12 - 22 |
CKSEL0 = 1 and SUT1..0 = 11 means:
| Crystal Oscillator, slowly rising power | |
| Start-up Time from Power-down and Power-save | 16000 clockcycles |
| Additional Delay from Reset (VCC = 5.0V) | 14 cClockcycles + 65ms |
CKSEL Device Clocking Options
Bits 3..0
| Bits | Description | Remark |
|---|---|---|
| 1111 - 1000 | Low power crystal oscillator | Works with a quartz crystal or a ceramic resonator |
| 0111 - 0110 | Full swing crystal oscillator | Is this a bug in the datasheet? CKSEL0=0 is mainly ceramic resonator |
| 0111 | Full swing crystal oscillator | 0,4-20MHz |
| 0101 | Low frequency crystal oscillator | Start-up time from Power-down and Power-save: 32K CK → Stable frequency at start-up |
| 0100 | Low frequency crystal oscillator | Start-up time from Power-down and Power-save 1K CK |
| 0011 | Internal 128kHz RC oscillator | |
| 0010 | Calibrated internal RC oscillator | Runs at nominal 8MHz (7,3 - 8,1 MHz). This is the default fuse setting |
| 0001 | Reserved | |
| 0000 | External clock |
High byte fuses
| Bit | Name | Description | Default Value | Remark |
|---|---|---|---|---|
| 7 | RSTDISBL | External Reset Disable | 1 | |
| 6 | DWEN | debugWIRE Enable | 1 | |
| 5 | SPIEN | Enable Serial Program and Data Downloading | 0 | SPI programming enabled |
| 4 | WDTON | Watchdog Timer Always On | 1 | |
| 3 | EESAVE | EEPROM memory is preserved through the Chip Erase | 1 | EEPROM not reserved |
| 2 | BOOTSZ1 | Select Boot Size | 0 | Change to 1 for Arduino when Optiboot is used |
| 1 | BOOTSZ0 | Select Boot Size | 0 | Change to 1 for Arduino when Optiboot is used |
| 0 | BOOTRST | Select Reset Vector | 1 | Change to 0 for Arduino |
The default value of the high fusebyte is 1101 1001 being 0xD9 in hex
For Arduino we need 1101 1110 being 0xDE in hex
For Arduino without bootloader we need 1101 1111 being 0xD? in hex. Also the IVSEL flag needs to be set in the MCUCR register
If no Boot Loader capability is needed, the entire Flash is available for application code
The Interrupt Vectors can be moved to the start of the Boot Flash section by setting the IVSEL bit in the MCU Control Register (MCUCR)
The Reset Vector can also be moved to the start of the Boot Flash section by programming the BOOTRST Fuse
BOOTSZ1..0 = 11 means:
| Boot Size | 128 words | |
| Pages | 4 | |
| Application Flash Section | 0x000 - 0xF7F | |
| Boot Loader Flash Section | 0xF80 - 0xFFF | |
| End Application Section | 0xF7F | |
| Boot Reset Address | 0xF80 | (Start Boot Loader Section) |
Extended byte fuses
| Bit | Name | Description | Default | Remark |
|---|---|---|---|---|
| 7 | ||||
| 6 | ||||
| 5 | ||||
| 4 | ||||
| 3 | ||||
| 2 | BODLEVEL2 | Brown-out Detector trigger level | 1 | |
| 1 | BODLEVEL1 | Brown-out Detector trigger level | 1 | Change to 0 for Arduino |
| 0 | BODLEVEL0 | Brown-out Detector trigger level | 1 |
The default value of the low fusebyte is 1111 1111 being 0xFF in hex
For Arduino we need 1111 1101 being 0xFD in hex
For Arduino without bootloader we need 1111 1101 being 0xFD in hex
BODLEVEL Fuse Coding
| Bits | Min. VBOT (V) | Typ VBOT (V) | Max VBOT (V) |
|---|---|---|---|
| 111 | BOD Disabled | BOD Disabled | BOD Disabled |
| 110 | 1,7 | 1,8 | 2,0 |
| 101 | 2,5 | 2,7 | 2,9 |
| 100 | 4.1 | 4,3 | 4,5 |
Boot Lock bits
For us all boot lock bits need to be set to 1 (high) so there is boot locking and all of flash can be programmed. This is the default value.
Reference
Useful links
Arduino ATmega 328p fuse settings
How to change fuse bits of AVR Atmega328p
ATmega 328 reading info
Search for atmega-fusebit-doctor-hvpp
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