Datasheet

15
XMEGA A4U [DATASHEET]
Atmel-8387H-AVR-ATxmega16A4U-34A4U-64A4U-128A4U-Datasheet_09/2014
7.3.4 Production Signature Row
The production signature row is a separate memory section for factory programmed data. It contains calibration data
for functions such as oscillators and analog modules. Some of the calibration values will be automatically loaded to
the corresponding module or peripheral unit during reset. Other values must be loaded from the signature row and
written to the corresponding peripheral registers from software. For details on calibration conditions, refer to “Electrical
Characteristics” on page 72.
The production signature row also contains an ID that identifies each microcontroller device type and a serial number
for each manufactured device. The serial number consists of the production lot number, wafer number, and wafer
coordinates for the device. The device ID for the available devices is shown in Table 7-2.
The production signature row cannot be written or erased, but it can be read from application software and external
programmers.
Table 7-2. Device ID bytes for Atmel AVR XMEGA A4U devices.
7.3.5 User Signature Row
The user signature row is a separate memory section that is fully accessible (read and write) from application software
and external programmers. It is one flash page in size, and is meant for static user parameter storage, such as
calibration data, custom serial number, identification numbers, random number seeds, etc. This section is not erased
by chip erase commands that erase the flash, and requires a dedicated erase command. This ensures parameter
storage during multiple program/erase operations and on-chip debug sessions.
7.4 Fuses and Lock bits
The fuses are used to configure important system functions, and can only be written from an external programmer.
The application software can read the fuses. The fuses are used to configure reset sources such as brownout detector
and watchdog, and startup configuration.
The lock bits are used to set protection levels for the different flash sections (that is, if read and/or write access should
be blocked). Lock bits can be written by external programmers and application software, but only to stricter protection
levels. Chip erase is the only way to erase the lock bits. To ensure that flash contents are protected even during chip
erase, the lock bits are erased after the rest of the flash memory has been erased.
An unprogrammed fuse or lock bit will have the value one, while a programmed fuse or lock bit will have the value
zero.
Both fuses and lock bits are reprogrammable like the flash program memory.
7.5 Data Memory
The data memory contains the I/O memory, internal SRAM, optionally memory mapped EEPROM, and external
memory if available. The data memory is organized as one continuous memory section, see Figure 7-1. To simplify
development, I/O Memory, EEPROM and SRAM will always have the same start addresses for all Atmel AVR
XMEGA devices.
Device Device ID bytes
Byte 2 Byte 1 Byte 0
ATxmega16A4U 41 94 1E
ATxmega32A4U 41 95 1E
ATxmega64A4U 46 96 1E
ATxmega128A4U 46 97 1E