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CHAPTER 3 CPU
MB89620 series
3.2 Dedicated Registers
3.2.1 Condition Code Register (CCR)
The condition code register (CCR) located in the lower 8 bits of the program status
(PS) consists of the C, V, Z, N, and H bits indicating the results of arithmetic
operations and the contents of transfer data, and the I, IL1, and IL0 bits for control
whether or not the CPU accepts interrupt requests.
n
Structure of Condition Code Register (CCR)
Figure 3.2.1a Structure of Condition Code Register
n
Arithmetic Operation Result Bits
l
Half-carry flag (H)
Set when a carry from bit 3 to bit 4 or a borrow from bit 4 to bit 3 occurs as a result of an
arithmetic operation. Cleared otherwise. As this flag is for the decimal adjustment instructions,
do not use this flag in cases other than addition or subtraction.
l
Negative flag (N)
Set if the most significant bit (MSB) is set to 1 as a result of an arithmetic operation. Cleared
when the bit is set to 0.
l
Zero flag (Z)
Set when an arithmetic operation results in 0. Cleared otherwise.
l
Overflow flag (V)
Set if the complement on 2 overflows as a result of an arithmetic operation. Reset if the overflow
does not occur.
l
Carry flag (C)
Set when a carry from bit 7 or borrow to bit 7 occurs as a result of an arithmetic operation. Cleared
otherwise. Set to the shift-out value in case of a shift instruction.
Figure 3.2.1b shows the change of the carry flag by a shift instruction.
Figure 3.2.1b Change of Carry Flag by Shift Instruction
Half-carry flag
Interrupt enable flag
Interrupt level bits
Negative flag
Zero flag
Overflow flag
Carry flag
Bit 15 Bit 14 Bit 13 Bit 12 Bit 11 Bit 10 Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
R4
R3
R2
R1
R0
—
—
—
H
I
IL1
IL0
N
Z
V
C
CCR initial value
X011XXXX
B
RP
CCR
PS
X: Indeterminate
C
Bit 7
Bit 0
Bit 7
Bit 0
• Left shift (ROLC)
• Right shift (RORC)
C
Summary of Contents for F2MC-8L MB89620 Series
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