Control Registers - Hitachi H8/329 Series Hardware Manual

3.2.2 Control Registers

The CPU control registers include a 16-bit program counter (PC) and an 8-bit condition code
register (CCR).
(1) Program Counter (PC): This 16-bit register indicates the address of the next instruction the
CPU will execute. Each instruction is accessed in 16 bits (1 word), so the least significant bit of the
PC is ignored (always regarded as 0).
(2) Condition Code Register (CCR): This 8-bit register contains internal status information,
including carry (C), overflow (V), zero (Z), negative (N), and half-carry (H) flags and the interrupt
mask bit (I).
Bit 7—Interrupt Mask Bit (I): When this bit is set to "1," all interrupts except NMI are masked.
This bit is set to "1" automatically by a reset and at the start of interrupt handling.
Bit 6—User Bit (U): This bit can be written and read by software (using the LDC, STC, ANDC,
ORC, and XORC instructions).
Bit 5—Half-Carry Flag (H): This flag is set to "1" when the ADD.B, ADDX.B, SUB.B,
SUBX.B, NEG.B, or CMP.B instruction causes a carry or borrow out of bit 3, and is cleared to "0"
otherwise. Similarly, it is set to "1" when the ADD.W, SUB.W, or CMP.W instruction causes a
carry or borrow out of bit 11, and cleared to "0" otherwise. It is used implicitly in the DAA and
DAS instructions.
Bit 4—User Bit (U): This bit can be written and read by software (using the LDC, STC, ANDC,
ORC, and XORC instructions).
SP
(R7)
Figure 3-2. Stack Pointer
25
Unused area
Stack area