4.9.2.3.1 SREG – Status
Register
| Name: | SREG |
| Offset: | 0x03F |
| Reset: | 0x00 |
| 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
The Global Interrupt
Enable bit (I bit) must be set for the interrupts to be enabled. The individual
interrupt enable control is then performed in separate control registers. If the I
bit is cleared, regardless of the individual interrupt enable settings none of the
interrupts are enabled. 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. See AVR Instruction Set Summary from Related
Links.
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
operated 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. See AVR Instruction Set Summary from Related
Links.
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 AVR Instruction Set Summary from Related Links.
Bit 3 – V Two's Complement Overflow Flag
The Two's Complement Overflow
Flag V supports two's complement arithmetic. See AVR Instruction Set Summary
from Related Links.
Bit 2 – N Negative Flag
The Negative Flag N indicates
a negative result in an arithmetic or logic operation. See AVR Instruction Set
Summary from Related Links.
Bit 1 – Z Zero Flag
The Zero Flag Z indicates a
‘0’ result in an arithmetic or logic operation. See AVR
Instruction Set Summary from Related Links.
Bit 0 – C Carry Flag
The Carry Flag C indicates a
carry in an arithmetic or logic operation. See AVR Instruction Set Summary
from Related Links.
