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8266D-MCU Wireless-06/12
ATmega128RFA1
The EEPROM Write Enable Signal EEPE is the write strobe to the EEPROM. When
address and data are correctly set up, the EEPE bit must be written to one to write the
value into the EEPROM. The EEMPE bit must be written to one before a logical one is
written to EEPE, otherwise no EEPROM write takes place. The following procedure
should be adopted when writing the EEPROM (the order of steps 3 and 4 is not
essential):
1. Wait until EEPE becomes zero.
2. Wait until SPMEN in SPMCSR becomes zero.
3. Write new EEPROM address to EEAR (optional).
4. Write new EEPROM data to EEDR (optional).
5. Write a logical one to the EEMPE bit while writing a zero to EEPE in EECR.
6. Within four clock cycles after setting EEMPE, write a logical one to EEPE.
The EEPROM can not be programmed during a CPU write to the Flash memory. The
software must check that the Flash programming is completed before initiating a new
EEPROM write. Step 2 is only relevant if the software contains a Boot Loader allowing
the CPU to program the Flash. If the Flash is never being updated by the CPU, step 2
can be omitted.
Caution: an interrupt between step 5 and step 6 will make the write cycle fail, since the
EEPROM Master Write Enable will time-out. If an interrupt routine accessing the
EEPROM is interrupting another EEPROM access, the EEAR or EEDR Register will be
modified, causing the interrupted EEPROM access to fail. It is recommended to have
the Global Interrupt Flag cleared during all steps to avoid these problems.
When the write access time has elapsed, the EEPE bit is cleared by hardware. The
user software can poll this bit and wait for a zero before writing the next byte. When
EEPE has been set, the CPU is halted for two cycles before the next instruction is
executed.
Bit 0 – EERE - EEPROM Read Enable
The EEPROM Read Enable Signal EERE is the read strobe to the EEPROM. When the
correct address is set up in the EEAR Register, the EERE bit must be written to a logic
one to trigger the EEPROM read. The EEPROM read access takes one instruction and
the requested data is available immediately. When the EEPROM is read, the CPU is
halted for four cycles before the next instruction is executed. The user should poll the
EEPE bit before starting the read operation. If a write operation is in progress, it is
neither possible to read the EEPROM nor to change the EEAR Register.
8.5 I/O Memory
The Input/Output (I/O) space definition of the ATmega128RFA1 is shown in
"RegisterAll ATmega128RFA1 I/Os and peripherals are placed in the I/O space. All I/O locations
may be accessed by the LD/LDS/LDD and ST/STS/STD 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 AVR instruction set 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,