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Rev. 1.0, 07/01, page 13 of 372
Bit Bit Name Initial Value R/W Description
7 I 1 R/W Interrupt Mask Bit
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 at the start of an exception-
handling sequence.
6 UI undefined R/W User Bit
Can be written and read by software using the
LDC, STC, ANDC, ORC, and XORC instructions.
5 H undefined R/W Half-Carry Flag
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.
4 U undefined R/W User Bit
Can be written and read by software using the
LDC, STC, ANDC, ORC, and XORC instructions.
3 N undefined R/W Negative Flag
Stores the value of the most significant bit of data
as a sign bit.
2 Z undefined R/W Zero Flag
Set to 1 to indicate zero data, and cleared to 0 to
indicate non-zero data.
1 V undefined R/W Overflow Flag
Set to 1 when an arithmetic overflow occurs, and
cleared to 0 at other times.
0 C undefined R/W Carry Flag
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 indicate a
carry
The carry flag is also used as a bit accumulator
by bit manipulation instructions.