ATA8741 ATMEL Corporation, ATA8741 Datasheet - Page 33

• Manufacturer Part Number: ATA8741
• Manufacturer: ATMEL Corporation

13.3
13.3.1
13.3.2
13.3.3
13.3.4
9140B–INDCO–07/09
EEPROM Data Memory
EEPROM Read/Write Access
Atomic Byte Programming
Split Byte Programming
Erase
The ATtiny24/44/84 contains 128/256/512 bytes of data EEPROM memory. It is organized as a
separate data space, in which single bytes can be read and written. The EEPROM has an
endurance of at least 100,000 write/erase cycles. The access between the EEPROM and the
CPU is described in the following, specifying the EEPROM Address Registers, the EEPROM
Data Register, and the EEPROM Control Register. For a detailed description of Serial data
downloading to the EEPROM, see
The EEPROM Access Registers are accessible in the I/O space.
The write access times for the EEPROM are given in
tion, however, lets the user software detect when the next byte can be written. If the user code
contains instructions that write the EEPROM, some precautions must be taken. In heavily fil-
tered power supplies, V
device for some period of time to run at a voltage lower than specified as minimum for the clock
frequency used. See
problems in these situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.
See
details on this.
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.
Using Atomic Byte Programming is the simplest mode. When writing a byte to the EEPROM, the
user must write the address into the EEARL 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 1. The EEPE bit remains set until the erase and write opera-
tions are completed. While the device is busy with programming, it is not possible to do any
other EEPROM operations.
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).
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 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.
“Atomic Byte Programming” on page 33
“Preventing EEPROM Corruption” on page 36
CC
is likely to rise or fall slowly on Power-up/down. This causes the
“Serial Downloading” on page
and
“Split Byte Programming” on page 33
Table 13-1 on page
184.
for details on how to avoid
39. A self-timing func-
ATA8741
for
33