10.5 I/O Memory

The I/O space definition of the device is shown in the Register Summary.

All device 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.

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. The device is a complex microcontroller with more peripheral units than can be supported within the 64 locations reserved in Opcode for the IN and OUT instructions. For the extended I/O space from 0x60..0xFF in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used.

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 '1' to them; this is described in the flag descriptions. 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 0x00-0x1F only.

The I/O and peripherals control registers are explained in later sections.