I/O Memory
The I/O space definition of the ATtiny2313 is shown in “Register Summary” on page
209.
All ATtiny2313 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 instruc-
tions. 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 registers 0x00 to 0x1F only.
The I/O and peripherals control registers are explained in later sections.
General Purpose I/O Registers The ATtiny2313 contains three General Purpose I/O Registers. These registers can be
used for storing any information, and they are particularly useful for storing global vari-
ables and status flags. General Purpose I/O Registers within the address range 0x00 -
0x1F are directly bit-accessible using the SBI, CBI, SBIS, and SBIC instructions.
General Purpose I/O Register
2 – GPIOR2
Bit
7
6
5
4
3
2
1
0
MSB
R/W
0
LSB
R/W
0
GPIOR2
GPIOR1
GPIOR0
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
General Purpose I/O Register
1 – GPIOR1
Bit
7
6
5
4
3
2
1
0
MSB
R/W
0
LSB
R/W
0
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
General Purpose I/O Register
0 – GPIOR0
Bit
7
6
5
4
3
2
1
0
MSB
R/W
0
LSB
R/W
0
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
20
ATtiny2313/V
2543F–AVR–08/04
ATMEL [ ATMEL ]
