Datasheet

Section 2 CPU
Rev. 3.00 Mar. 15, 2006 Page 14 of 526
REJ09B0060-0300
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.