Status register

A status register (also: flag register or condition code register (CCR)) is a collection of flag bits for a processor. A popular example of a status register is the FLAGS register of x86 architecture based microprocessors.

Common status register flags

Flag	Name	Description
Z	Zero flag	Indicates that the result of a mathematical or logical operation was zero.
C	Carry flag	Indicates that the result of an operation produced an answer greater than the number of available bits. (This flag may also be set before a mathematical operation as an extra operand to certain instructions, e.g. "add with carry".)
X	Extend flag	Masks the XIRQ request when set. It is set by the hardware and cleared by the software as well is set by unmaskable XIRQ.
N / S	Negative / Sign flag	Indicates that the result of a mathematical operation is negative. In some processors, the N and S flags have different meanings: the S flag indicates whether a subtraction or addition has taken place, whereas the N flag indicates whether the last operation result is positive or negative.
V / O / W	Overflow flag	Indicates that the result of an operation has overflowed according to the CPU's word representation, similar to the carry flag but for signed operations.
I / E	Interrupt enable flag	Interrupts can be enabled or disabled by respectively setting or clearing this flag. Modifying this flag may be restricted to programs executing in supervisor mode.
P	Parity flag	Indicate that the number of bits of the result is odd or even.
D / T	Debug / Trap flag	Specifies that a special tracing interrupt or exception is generated immediately after each single instruction is executed. This is used to implement program code debuggers.

See also

• [[Flag byt
• Flag (computing)
• FLAGS register (computing)
• Program status word
• Control register