ATtiny48 datasheet(19/266 Pages) ATMEL

19 / 266 page

8008C–AVR–03/09

ATtiny48/88

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 Figure 5-1 on page 23. The EEPE bit remains set until the erase

and write operations are completed. While the device is busy with programming, it is not possi-

ble to do any other EEPROM operations.

5.3.3

Split Byte Programming

It is possible to split the erase/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 advantage of this method, it is required that the locations to be

written have been erased before the write operation.

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 (program-

ming time is given in Figure 5-1 on page 23). 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 (programming time is given in Figure 5-1 on page 23). 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 “OSCCAL – Oscillator Calibration Register” on

page 31.

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.

Assembly Code Example

EEPROM_write:

; Wait for completion of previous write

sbic

EECR,EEPE

rjmp

EEPROM_write

; Set up address (r17) in address register

out

EEARL, r17

; Write data (r19) to Data Register

out

EEDR,r19

; Write logical one to EEMPE

sbi

EECR,EEMPE

; Start eeprom write by setting EEPE

sbi

EECR,EEPE

ret

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