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 AVR’s, 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.
4.5
General Purpose I/O Registers
The Atmel® ATmega16/32/64/M1/C1 contains 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 status flags.
The general purpose I/O registers, within the address range 0x00 - 0x1F, are directly bit-accessible using the SBI, CBI,
SBIS, and SBIC instructions.
4.5.1 General Purpose I/O Register 0 – GPIOR0
Bit
7
6
5
4
3
2
1
0
GPIOR07 GPIOR06 GPIOR05 GPIOR04 GPIOR03 GPIOR02 GPIOR01 GPIOR00 GPIOR0
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
4.5.2 General Purpose I/O Register 1 – GPIOR1
Bit
7
6
5
4
3
2
1
0
GPIOR17 GPIOR16 GPIOR15 GPIOR14 GPIOR13 GPIOR12 GPIOR11 GPIOR10 GPIOR1
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
4.5.3 General Purpose I/O Register 2 – GPIOR2
Bit
7
6
5
4
3
2
1
0
GPIOR27 GPIOR26 GPIOR25 GPIOR24 GPIOR23 GPIOR22 GPIOR21 GPIOR20 GPIOR2
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
24
ATmega16/32/64/M1/C1 [DATASHEET]
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
