attiny167-esxz ATMEL Corporation, attiny167-esxz Datasheet - Page 17

• Manufacturer Part Number: attiny167-esxz
• Description: 8-bit Avr 8-bit Microcontroller Microcontroller With 16k Bytes In-system Programmable Flash And Lin Controller
• Manufacturer: ATMEL Corporation

3.3.2
3.3.3
3.3.4
3.3.5
7728A–AUTO–07/08
Atomic Byte Programming
Split Byte Programming
Erase
Write
The write access times for the EEPROM are given in
lets the user software detect when the next byte can be written. If the user code contains instruc-
tions that write the EEPROM, some precautions must be taken. In heavily filtered power
supplies, Vcc is likely to rise or fall slowly on Power-up/down. This causes the device for some
period of time to run at a voltage lower than specified as minimum for the clock frequency used.
See
situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.
Refer to
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
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. 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.
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 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
page
”Preventing EEPROM Corruption” on page 19
36.
”Atomic Byte Programming” on page 17
”OSCCAL – Oscillator Calibration Register” on
and
for details on how to avoid problems in these
Table
”Split Byte Programming” on page 17
3-2. A self-timing function, however,
ATtiny167
for
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