ATMEGA48V_11 ATMEL [ATMEL Corporation], ATMEGA48V_11 Datasheet - Page 11

• Manufacturer Part Number: ATMEGA48V_11
• Description: 8-bit Atmel Microcontroller with 4/8/16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

7.4
7.4.1
2545T–AVR–05/11
Status register
SREG – AVR Status Register
The Status Register contains information about the result of the most recently executed arithme-
tic instruction. This information can be used for altering program flow in order to perform
conditional operations. Note that the Status Register is updated after all ALU operations, as
specified in the
dedicated compare instructions, resulting in faster and more compact code.
The Status Register is not automatically stored when entering an interrupt routine and restored
when returning from an interrupt. This must be handled by software.
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 inter-
rupt 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
• Bit 6 – T: Bit copy storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or desti-
nation 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 the
• Bit 4 – S: Sign bit, S = N
The S-bit is always an exclusive or between the Negative Flag N and the Two’s Complement
Overflow Flag V. See the
• Bit 3 – V: Two’s complement overflow flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the
“Instruction Set
• Bit 2 – N: Negative flag
The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the
“Instruction Set
• Bit 1 – Z: Zero flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the
Set
Bit
0x3F (0x5F)
Read/write
Initial value
Description” for detailed information.
Instruction Set
Description” for detailed information.
Description” for detailed information.
R/W
7
0
I
R/W
“Instruction Set
6
T
0
“Instruction Set
⊕
Reference. This will in many cases remove the need for using the
V
R/W
H
5
0
Description” for detailed information.
Description” for detailed information.
R/W
S
4
0
R/W
V
3
0
ATmega48/88/168
R/W
N
2
0
instruction set
R/W
Z
1
0
R/W
C
0
0
reference.
“Instruction
SREG
11