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Bit 7—Interrupt Mask Bit (I): Masks interrupts other than NMI when set to 1. (NMI is accepted
regardless of the I bit setting.) The I bit is set to 1 by hardware at the start of an exception-
handling sequence. For details, refer to section 5, Interrupt Controller.
Bit 6—User Bit or Interrupt Mask Bit (UI): Can be written and read by software using the
LDC, STC, ANDC, ORC, and XORC instructions. With the H8S/2319 and H8S/2318 Groups, this
bit cannot be used as an interrupt mask bit.
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 cleared to 0
otherwise. When the ADD.W, SUB.W, CMP.W, or NEG.W instruction is executed, the H flag is
set to 1 if there is a carry or borrow at bit 11, and cleared to 0 otherwise. When the ADD.L,
SUB.L, CMP.L, or NEG.L instruction is executed, the H flag is set to 1 if there is a carry or
borrow at bit 27, and cleared to 0 otherwise.
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): Stores the value of 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 some or all of the flag bits unchanged. For the action of each instruction
on the flag bits, refer to Appendix A.1, Instruction List.
Operations can be performed on the CCR bits by the LDC, STC, ANDC, ORC, and XORC
instructions. The N, Z, V, and C flags are used as branching conditions for conditional branch
(Bcc) instructions.
2.4.4
Initial Register Values
Reset exception handling loads the CPU's program counter (PC) from the vector table, clears the
trace bit in EXR to 0, and sets the interrupt mask bits in CCR and EXR to 1. The other CCR bits
and the general registers are not initialized. In particular, the stack pointer (ER7) is not initialized.
Rev. 5.00, 12/03, page 35 of 1088
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