All ATtiny202/204/402/404/406 I/Os and peripherals are
located in the I/O memory space. The I/O address range from 0x00 to 0x3F can be accessed
in a single cycle using IN and OUT instructions. The
extended I/O memory space from 0x0040 to 0x0FFF can 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 memory
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.
For compatibility with future devices, reserved bits must be written to ‘0’ if accessed. Reserved I/O memory addresses must never be written.
Some of the interrupt flags are cleared by writing a ‘1’ to them. On ATtiny202/204/402/404/406 devices, the
CBI and SBI instructions will only operate on the
specified bit and can be used on registers containing such interrupt flags. The
CBI and SBI instructions work with registers
0x00-0x1F only.
The ATtiny202/204/402/404/406 devices provide four general
purpose I/O registers. These registers can be used for storing any information, and they
are particularly useful for storing global variables and interrupt flags. General
purpose I/O registers, which reside in the address range 0x1C-0x1F, are directly
bit-accessible using the SBI, CBI,
SBIS, and SBIC instructions.