Datasheet

ATmega16U4/32U4 [DATASHEET]

Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016

All 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. The device 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

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 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.

5.4.1 General Purpose I/O Registers

The device contains three General Purpose I/O Registers. These registers can be used for storing any

information, and they are particularly useful for storing global variables 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 Value 0 0 0 0 0 0 0 0

Bit 76543210

MSB LSB GPIOR0

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0