17
ATmega8515(L)
2512A–AVR–04/02
EEPROM Data Memory The ATmega8515 contains 512 bytes ofdata EEPROM memory. Itis organized as a
separate data space, in which single bytescan be read andwritten. The EEPROM has
an enduranceof at least100,000 write/erase cycles.Theaccess between the EEPROM
and the CPU isdescribed in the following,specifying the EEPROM Address Registers,
the EEPROM Data Register, and the EEPROM Control Register.
For a detaileddescription ofSPIdata downloading to the EEPROM, see page 189.
EEPROM Read/Write Access The EEPROM Access Registers areaccessibleinthe I/Ospace.
The write access time for the EEPROM is given in Table1.Aself-timing function,how-
ever, lets theusersoftware detect when thenext byte can be written. If theusercode
contains instructions that write the EEPROM, some precautions must betaken. In
heavily filteredpowersupplies, V
CC
islikely to riseorfall slowly on Power-up/down. This
causes the device forsome period of time to run at a voltage lower than specified as
minimum for the clock frequency used. See “Preventing EEPROM Corruption” on page
21. fordetails on how to avoidproblems in these situations.
Inorder to prevent unintentionalEEPROM writes, a specificwrite proceduremust be fol-
lowed.Refer to the description of the EEPROM Control Registerfordetails on this.
When the EEPROM isread, the CPU ishaltedforfourclock cyclesbeforethenext
instruction is executed. When the EEPROM iswritten, the CPU ishaltedfor two clock
cyclesbeforethenextinstruction is executed.
The EEPROM Address
Register – EEARH and EEARL
• Bits 15..9 – Res: Reserved Bits
These bits are reservedbits in the ATmega8515 andwill always read aszero.
• Bits 8..0 – EEAR8..0: EEPROM Address
The EEPROM Address Registers – EEARH andEEARL – specify the EEPROM
address in the512bytesEEPROM space. The EEPROM data bytes areaddressedlin-
early between0and 511. Theinitial value ofEEAR is undefined.Aproper value must be
written beforethe EEPROM maybeaccessed.
The EEPROM Data Register –
EEDR
• Bits 7..0 – EEDR7.0: EEPROM Data
For the EEPROM write operation, the EEDR Registercontains the data to be written to
the EEPROM in theaddress given by the EEAR Register. For the EEPROM read oper-
ation, the EEDR contains the data read out from the EEPROM at theaddress given by
EEAR.
Bit 15 14 13 12 11 10 9 8
–––––––EEAR8EEARH
EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL
76543 210
Read/WriteRRRRRRRR/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value0000000X
XXXXXXXX
Bit 76543 210
MSB LSB EEDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
(24 páginas)
Manymanuals.com
Manymanuals.de
Manymanuals.fr
Manymanuals.it
Manymanuals.pl
Manymanuals.cz
Manymanuals.es
Manymanuals-pt.com
Comentários a estes Manuais