2. CPU
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ORC, and XORC instructions). The N, Z, V, and C flags are used as branching conditions for
conditional branching (Bcc) instructions.
Bit 7—Interrupt Mask Bit (I):
When this bit is set to 1, interrupts are masked. This bit is set to 1
automatically at the start of exception handling. The interrupt mask bit may be read and written by
software. For further details, see section 3.3, Interrupts.
Bit 6—User Bit (U):
Can be used freely by the user.
Bit 5—Half-Carry Flag (H):
When the ADD.B, ADDX.B, SUB.B, SUBX.B, CMP.B, or NEG.B
instruction is executed, this flag is set to 1 if there is a carry or borrow at bit 3, and is cleared to 0
otherwise.
The H flag is used implicitly by the DAA and DAS instructions.
When the ADD.W, SUB.W, or CMP.W instruction is executed, the H flag is set to 1 if there is a
carry or borrow at bit 11, and is cleared to 0 otherwise.
Bit 4—User Bit (U):
Can be used freely by the user.
Bit 3—Negative Flag (N):
Indicates the most significant bit (sign bit) of the result of an
instruction.
Bit 2—Zero Flag (Z):
Set to 1 to indicate a zero result, and cleared to 0 to indicate a non-zero
result.
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 operation execution generates a carry, and cleared to 0
otherwise. Used by:
•
Add instructions, to indicate a carry
•
Subtract instructions, to indicate a borrow
•
Shift and rotate instructions
The carry flag is also used as a bit accumulator by bit manipulation instructions.
Some instructions leave some or all of the flag bits unchanged.
Refer to the
H8/300L Series Software Manual
for the action of each instruction on the flag bits.
Summary of Contents for F-ZTAT H8 Series
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