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Status register
From Wikipedia, the free encyclopedia
(Redirected from Flag 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.
- Z = Zero flag. Indicates whether the result of a mathematical or logical operation was zero
- C = Carry flag. Indicates whether 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)
- N (sometimes S) = Negative or Sign flag. Indicates whether the result of a mathematical operation is negative. In the TLCS-900 series of Toshiba microcontrollers, the N flag and S flag 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 (see PDF page 10 of the official operation manual).
- V (sometimes O or W) = Overflow flag. Indicates whether the result of an operation has overflowed according to the two's complement representation. (Similar to the carry flag but for signed operations)
- I = Interrupt enable flag. Interrupts can be enabled or disabled by respectively setting or clearing this flag
- P = Parity flag. Indicate whether the number of bits of the result is odd or even