Datasheet

11.4.2. EEPROM Write during Power-down Sleep Mode
When entering Power-down sleep mode while an EEPROM write operation is active, the EEPROM write
operation will continue, and will complete before the Write Access time has passed. However, when the
write operation is completed, the Oscillator continues running, and as a consequence, the device does
not enter Power-down entirely. It is therefore recommended to verify that the EEPROM write operation is
completed before entering Power-down.
11.4.3. Preventing EEPROM Corruption
During periods of low V
CC,
the EEPROM data can be corrupted because the supply voltage is too low for
the CPU and the EEPROM to operate properly. These issues are the same as for board level systems
using EEPROM, and the same design solutions should be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too low. First, a regular
write sequence to the EEPROM requires a minimum voltage to operate correctly. Second, the CPU itself
can execute instructions incorrectly, if the supply voltage is too low.
EEPROM data corruption can easily be avoided by following this design recommendation:
Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can be done
by enabling the internal Brown-out Detector (BOD). If the detection level of the internal BOD does not
match the needed detection level, an external low V
CC
Reset Protection circuit can be used. If a reset
occurs while a write operation is in progress, the write operation will be completed provided that the
power supply voltage is sufficient.
11.5. I/O Memory
The I/O space definition of the ATmega32A is shown in Register Summary.
All ATmega32A I/Os and peripherals are placed in the I/O space. The I/O locations are accessed by the
IN and OUT instructions, transferring data between the 32 general purpose working registers and the I/O
space. I/O Registers within the address range 0x00 - 0x1F are directly bit-accessible using the SBI and
CBI instructions. In these registers, the value of single bits can be checked by using the SBIS and SBIC
instructions. Refer to the instruction set section for more details. When using the I/O specific commands
IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing I/O Registers as data space
using LD and ST instructions, 0x20 must be added to these addresses.
For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O
memory addresses should never be written.
Some of the Status Flags are cleared by writing a logical one to them. Note that the CBI and SBI
instructions will operate on all bits in the I/O Register, writing a one back into any flag read as set, thus
clearing the flag. The CBI and SBI instructions work with registers 0x00 to 0x1F only.
The I/O and Peripherals Control Registers are explained in later sections.
Related Links
Register Summary on page 399
11.6. Register Description
Atmel ATmega32A [DATASHEET]
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