Datasheet
ATmega164A/PA/324A/PA/644A/PA/1284/P
2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 20
7.3.1 SREG – Status Register
(1)
The AVR Status Register – SREG – is defined as:
• Bit 7 – I: Global Interrupt Enable
The Global Interrupt Enable bit must be set for the interrupts to be enabled. 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
AVR Instruction Set Manual on www.microchip.com.
• 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.
• 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.
• 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.
Note: 1. Refer to the Instruction Set Manual on www.microchip.com for more details
Bit 76543210
0x3F (0x5F) ITHSVNZCSREG
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000