Datasheet

26
7766F–AVR–11/10
ATmega16/32U4
5.4 I/O Memory
The I/O space definition of the ATmega16U4/ATmega32U4 is shown in “Register Summary” on
page 408.
All ATmega16U4/ATmega32U4 I/Os and peripherals are placed in the I/O space. All I/O loca-
tions 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. The
ATmega16U4/ATmega32U4 is a complex microcontroller with more peripheral units than can be
supported within the 64 location 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 instruc-
tions 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 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.
5.4.1 General Purpose I/O Registers
The ATmega16U4/ATmega32U4 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.
5.4.2 General Purpose I/O Register 2 – GPIOR2
5.4.3 General Purpose I/O Register 1 – GPIOR1
5.4.4 General Purpose I/O Register 0 – GPIOR0
Bit 76543210
MSB LSB GPIOR2
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
MSB LSB GPIOR1
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
MSB LSB GPIOR0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000