Datasheet

13
8493A–AVR–02/12
XMEGA C4
7.3.4 Production Signature Row
The production signature row is a separate memory section for factory programmed data. It con-
tains 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 correspond-
ing peripheral registers from software. For details on calibration conditions, refer to ”Electrical
Characteristics TBD” on page 64.
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 7-1.
The production signature row cannot be written or erased, but it can be read from application
software and external programmers.
Table 7-1. Device ID bytes.
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 dur-
ing 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 config-
ure 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
Device Device ID bytes
Byte 2 Byte 1 Byte 0
ATxmega32C4 43 94 1E
ATxmega16C4 44 95 1E