8.7.3 Status Register
The Status register contains information about the result of the most recently executed arithmetic or logic instruction. For details about the bits in this register and how they are affected by the different instructions, see the Instruction Set Summary.
Name: | SREG |
Offset: | 0x0F |
Reset: | 0x00 |
Property: | - |
Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
I | T | H | S | V | N | Z | C | ||
Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | R/W | |
Reset | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Bit 7 – I Global Interrupt Enable
Writing a '1' to this bit enable interrupts on the device.
Writing a '0' to this bit disables interrupts on the device, independent of the individual interrupt enable settings of the peripherals.
This bit is not cleared by hardware after an interrupt has occurred.
This bit can be set and cleared by software with the SEI and CLI instructions.
Changing the I flag through the I/O-register result in a one-cycle wait state on the access.
Bit 6 – T Bit Copy Storage
The bit copy instructions bit load (BLD
) and bit
store (BST
) use the T bit as source or destination for the
operated bit.
A bit from a register in the register file can be copied into this
bit by the BST
instruction, and this bit can be copied into a
bit in a register in the register file by the BLD
instruction.
Bit 5 – H Half Carry Flag
This bit indicates a half carry in some arithmetic operations. Half carry is useful in BCD arithmetic.
Bit 4 – S Sign Bit, S = N ⊕ V
The sign bit (S) is always an exclusive or (xor) between the negative flag (N) and the two’s complement overflow flag (V).
Bit 3 – V Two’s Complement Overflow Flag
The two’s complement overflow flag (V) supports two’s complement arithmetic.
Bit 2 – N Negative Flag
The negative flag (N) indicates a negative result in an arithmetic or logic operation.
Bit 1 – Z Zero Flag
The zero flag (Z) indicates a zero result in an arithmetic or logic operation.
Bit 0 – C Carry Flag
The carry flag (C) indicates a carry in an arithmetic or logic operation.