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Bit 4—User Bit (U): Can be written and read by software using the LDC, STC, ANDC, ORC, and
XORC instructions.
Bit 3—Negative Flag (N): Indicates the most significant bit (sign bit) of data.
Bit 2—Zero Flag (Z): Set to 1 to indicate zero data, and cleared to 0 to indicate non-zero data.
Bit 1—Overflow Flag (V): Set to 1 when an arithmetic overflow occurs, and cleared to 0 at other
times.
Bit 0—Carry Flag (C): Set to 1 when a carry occurs, and cleared to 0 otherwise. Used by:
• Add instructions, to indicate a carry
• Subtract instructions, to indicate a borrow
• Shift and rotate instructions, to store the value shifted out of the end bit
The carry flag is also used as a bit accumulator by bit manipulation instructions.
Some instructions leave flag bits unchanged. Operations can be performed on CCR by the LDC,
STC, ANDC, ORC, and XORC instructions. The N, Z, V, and C flags are used by conditional
branch (Bcc) instructions.
For the action of each instruction on the flag bits, see appendix A.1, Instruction List.
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