H8SLASH3021 datasheet(46/712 Pages) RENESAS

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2. CPU

Rev.2.00 Mar. 22, 2007 Page 22 of 684

REJ09B0352-0200

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): 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. For the I and

UI bits, see section 5, Interrupt Controller.

2.4.4

Initial CPU Register Values

In reset exception handling, PC is initialized to a value loaded from the vector table, and the I bit

in CCR is set to 1. The other CCR bits and the general registers are not initialized. In particular,

the stack pointer (ER7) is not initialized. The stack pointer must therefore be initialized by an

MOV.L instruction executed immediately after a reset.

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