Datasheet
17
ATtiny25/45/85 [DATASHEET]
2586Q–AVR–08/2013
When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is executed. When
the EEPROM is written, the CPU is halted for two clock cycles before the next instruction is executed.
5.3.2 Atomic Byte Programming
Using Atomic Byte Programming is the simplest mode. When writing a byte to the EEPROM, the user must write
the address into the EEAR Register and data into EEDR Register. If the EEPMn bits are zero, writing EEPE (within
four cycles after EEMPE is written) will trigger the erase/write operation. Both the erase and write cycle are done in
one operation and the total programming time is given in Table 5-1 on page 21. The EEPE bit remains set until the
erase and write operations are completed. While the device is busy with programming, it is not possible to do any
other EEPROM operations.
5.3.3 Split Byte Programming
It is possible to split the erase and write cycle in two different operations. This may be useful if the system requires
short access time for some limited period of time (typically if the power supply voltage falls). In order to take advan-
tage of this method, it is required that the locations to be written have been erased before the write operation. But
since the erase and write operations are split, it is possible to do the erase operations when the system allows
doing time-critical operations (typically after Power-up).
5.3.4 Erase
To erase a byte, the address must be written to EEAR. If the EEPMn bits are 0b01, writing the EEPE (within four
cycles after EEMPE is written) will trigger the erase operation only (programming time is given in Table 5-1 on
page 21). The EEPE bit remains set until the erase operation completes. While the device is busy programming, it
is not possible to do any other EEPROM operations.
5.3.5 Write
To write a location, the user must write the address into EEAR and the data into EEDR. If the EEPMn bits are
0b10, writing the EEPE (within four cycles after EEMPE is written) will trigger the write operation only (program-
ming time is given in Table 5-1 on page 21). The EEPE bit remains set until the write operation completes. If the
location to be written has not been erased before write, the data that is stored must be considered as lost. While
the device is busy with programming, it is not possible to do any other EEPROM operations.
The calibrated Oscillator is used to time the EEPROM accesses. Make sure the Oscillator frequency is within the
requirements described in “OSCCAL – Oscillator Calibration Register” on page 31.