
20
8126F–AVR–05/12
ATtiny13A
5.4
I/O Memory
The I/O space definition of the ATtiny13A is shown in
“Register Summary” on page 158
All ATtiny13A I/Os and peripherals are placed in the I/O space. All I/O locations may be
accessed by the LD/LDS/LDD and ST/STS/STD instructions, transferring data between the 32
general purpose working registers and the I/O space. I/O Registers within the address range
0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these registers, the
value of single bits can be checked by using the SBIS and SBIC instructions. Refer to the
instruction set section for more details. When using the I/O specific commands IN and OUT, the
I/O addresses 0x00 - 0x3F must be used. When addressing I/O Registers as data space using
LD and ST instructions, 0x20 must be added to these addresses.
For compatibility with future devices, reserved bits should be written to zero if accessed.
Reserved I/O memory addresses should never be written.
Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike most
other AVRs, the CBI and SBI instructions will only operate on the specified bit, and can therefore
be used on registers containing such Status Flags. The CBI and SBI instructions work with reg-
isters 0x00 to 0x1F only.
The I/O and Peripherals Control Registers are explained in later sections.
5.5
Register Description
5.5.1
EEARL – EEPROM Address Register
• Bits 7:6 – Res: Reserved Bits
These bits are reserved bits in the ATtiny13A and will always read as zero.
• Bits 5:0 – EEAR[5:0]: EEPROM Address
The EEPROM Address Register – EEARL – specifies the EEPROM address in the 64 bytes
EEPROM space. The EEPROM data bytes are addressed linearly between 0 and 63. The initial
value of EEARL is undefined. A proper value must be written before the EEPROM may be
accessed.
5.5.2
EEDR – EEPROM Data Register
• Bits 7:0 – EEDR[7:0]: EEPROM Data
For the EEPROM write operation the EEDR Register contains the data to be written to the
EEPROM in the address given by the EEARL Register. For the EEPROM read operation, the
EEDR contains the data read out from the EEPROM at the address given by EEARL.
Bit
7
6
5
4
3
2
1
0
–
–
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
EEARL
Read/Write
R
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
X
X
X
X
X
X
Bit
7
6
5
4
3
2
1
0
EEDR7
EEDR6
EEDR5
EEDR4
EEDR3
EEDR2
EEDR1
EEDR0
EEDR
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
X
X
X
X
X
X
X
X