20
ATmega16M1/32M1/64M1 [DATASHEET]
8209E–AVR–11/2012
Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can be done by
enabling the internal Brown-out Detector (BOD). If the detection level of the internal BOD does not match the
needed detection level, an external low V
CC reset Protection circuit can be used. If a reset occurs while a write
operation is in progress, the write operation will be completed provided that the power supply voltage is sufficient.
7.5
I/O Memory
All ATmega16M1/32M1/64M1 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 reg-
isters 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 ATmega16M1/32M1/64M1 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 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.
7.6
General purpose I/O registers
The ATmega16M1/32M1/64M1 contains four General Purpose I/O Registers. These registers can be used for stor-
ing any information, and they are particularly useful for storing global variables and status flags. See
“RegisterThe General Purpose I/O Registers, within the address range 0x00 - 0x1F, are directly bit-accessible using the
SBI, CBI, SBIS, and SBIC instructions.