E.3 Modern AVR Parts

Modern 8-bit AVR devices have the following memories in addition to eeprom, flash, signature and lock:

fuse0

A.k.a. wdtcfg: watchdog configuration

fuse1

A.k.a. bodcfg: brownout detection configuration

fuse2

A.k.a. osccfg: oscillator configuration

fuse3

A.k.a. pincfg (not all devices): UPDI and reset pin configuration

fuse4

A.k.a. tcd0cfg (not all devices): timer counter type D configuration
A.k.a. hwmoncfg (not all devices): CPU safety function checks for illegal opcodes

fuse5

A.k.a. syscfg0: system configuration 0

fuse6

A.k.a. syscfg1: system configuration 1

fuse7

A.k.a. append or codesize: either the end of the application code section or the code size in blocks of 256/512 bytes

fuse8

A.k.a. bootend or bootsize: end of the boot section or the boot size in blocks of 256/512 bytes

fusea

A.k.a. pdicfg: configures/locks updi access; it is the only fuse that consists of two bytes

fuses

A logical memory of up to 16 bytes containing all fuseX of a part, which can be used to program all fuses at the same time

osc16err

Two bytes typically describing the 16 MHz oscillator frequency error at 3 V and 5 V, respectively (not all devices)

osc20err

Two bytes typically describing the 20 MHz oscillator frequency error at 3 V and 5 V, respectively (not all devices)

osccal16

One or two oscillator calibration bytes for 16 MHz (not all devices)

osccal20

One or two oscillator calibration bytes for 20 MHz (not all devices)

prodsig

Read-only memory section for factory programmed data such as the signature, calibration values and serial number

sigrow

Memory alias for prodsig

sernum

Serial number with a unique ID for the part (10 or 16 bytes)

tempsense

Temperature sensor calibration values

bootrow

Extra page of memory that is only accessible by the MCU in bootloader code; UDPI can read and write this memory only when the device is unlocked

userrow

Extra page of EEPROM memory that can be used for firmware settings; this memory is not erased during a chip erase

sib

Special system information block memory with information about AVR family, chip revision etc.

io

Volatile register memory; AVRDUDE can program this memory but this is of limited utility because anything written to the io memory will be undefined or lost after reset; writing to individual registers in the terminal can still be used, e.g., to test I/O ports

sram

Volatile RAM memory; can be read and written but contents will be lost after reset

This document was generated on July 11, 2026 using texi2html 5.0.