11
ATmega16M1/32M1/64M1 [DATASHEET]
8209E–AVR–11/2012
6.3.1
SREG – AVR Status Register
Bit 7 – I: Global Interrupt Enable
The Global Interrupt Enable bit must be set to enabled the interrupts. The individual interrupt enable control is then
performed in separate control registers. If the Global Interrupt Enable Register is cleared, none of the interrupts are
enabled independent of the individual interrupt enable settings. The I-bit is cleared by hardware after an interrupt
has occurred, and is set by the RETI instruction to enable subsequent interrupts. The I-bit can also be set and
cleared by the application with the SEI and CLI instructions, as described in the instruction set reference.
Bit 6 – T: Bit Copy Storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or destination for the oper-
ated bit. A bit from a register in the Register File can be copied into T by the BST instruction, and a bit in T can be
copied into a bit in a register in the Register File by the BLD instruction.
Bit 5 – H: Half Carry Flag
The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry Is useful in BCD arithmetic.
Bit 4 – S: Sign Bit, S = N
V
The S-bit is always an exclusive or between the negative flag N and the Two’s Complement Overflow Flag V. See
Bit 3 – V: Two’s Complement Overflow Flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the
“Instruction set sum- Bit 2 – N: Negative Flag
The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the
“Instruction set sum- Bit 1 – Z: Zero Flag
Bit 0 – C: Carry Flag
319 for detailed information.
Bit
7
6
5
4
3210
IT
H
S
V
N
Z
C
SREG
Read/write
R/W
Initial value
0
0000