5 condition code register (ccr), Condition code register (ccr) – Freescale Semiconductor MC68HC08KH12 User Manual
Page 57
MC68HC(7)08KH12
—
Rev. 1.1
Advance Information
Freescale Semiconductor
57
6.4.5 Condition Code Register (CCR)
The 8-bit condition code register contains the interrupt mask and five
flags that indicate the results of the instruction just executed. Bits 6 and
5 are set permanently to logic one. The following paragraphs describe
the functions of the condition code register.
V — Overflow Flag
The CPU sets the overflow flag when a two's complement overflow
occurs. The signed branch instructions BGT, BGE, BLE, and BLT use
the overflow flag.
1 = Overflow
0 = No overflow
H — Half-Carry Flag
The CPU sets the half-carry flag when a carry occurs between
accumulator bits 3 and 4 during an ADD or ADC operation. The half-
carry flag is required for binary-coded decimal (BCD) arithmetic
operations. The DAA instruction uses the states of the H and C flags
to determine the appropriate correction factor.
1 = Carry between bits 3 and 4
0 = No carry between bits 3 and 4
Bit 7
6
5
4
3
2
1
Bit 0
Read:
V
1
1
H
I
N
Z
C
Write:
Reset:
X
1
1
X
1
X
X
X
X = Indeterminate
Figure 6-6. Condition Code Register (CCR)