ATtiny25 datasheet(18/196 Pages) ATMEL

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7598H–AVR–07/09

ATtiny25/45/85

5.3.6

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 20-1. 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.

5.3.7

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 sup-

ply voltage falls). In order to take advantage 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).

5.3.8

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 (program-

ming time is given in Table 20-1). 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.

5.3.9

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 (programming time is given in Table 20-1). 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 fre-

quency is within the requirements described in “Oscillator Calibration Register – OSCCAL” on

page 26.

The following code examples show one assembly and one C function for erase, write, or atomic

write of the EEPROM. The examples assume that interrupts are controlled (e.g., by disabling

interrupts globally) so that no interrupts will occur during execution of these functions

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