Motorola M6800 User Manual
Page 7
MPU-7
Carry-Borrow:
For addition, the carry-borrow condition code (C) in the
zero bit position, represents a carry. This bit gets set
(C=1) to indicate a carry, and is reset (C=0) if there is
no carry.
For subtraction, the C bit is set (C=1) to indicate a
borrow and is reset (C=0) to indicate there was no borrow.
Overflow:
The V bit (bit 1) of the condition code register is set
(V=1) when two's complement overflow results from an
arithmetic operation, and is reset (V=O) if two's
complement overflow does not occur.
Zero:
The Z bit (bit 2) of the condition code register is set
(Z=1) if the result of an arithmetic operation is zero, and
is reset (Z=0) if the result is not zero.
Negative:
The N bit (bit 3) of the condition code register is set
(N=1) if bit 7 of an arithmetic operation is set (equal to
1). This indicates that the two's complement number,
represented by the bit pattern of the result, is negative.
The N bit is reset (N=0) if bit 7 of the arithmetic result
is equal to 0.
Interrupt Mask: If this I bit (bit 4) is set (I=1), the MPU cannot respond
to an interrupt request from any peripheral device.
Half-Carry:
The half carry bit H (bit 5) of the condition code register
is set (H=1) during execution of any of the instructions
ABA,ADC, or ADD, if there is a carry from bit position 3 to
bit position 4. The half carry is reset (H=0) during these
operations, if there is no carry from bit position 4.