
C165H
Central Processor Unit
Data Sheet
69
2001-04-19
PRELMNARY
for a prioritize ALU operation, because a '1' is never shifted out of the MSB during the
normalization of an operand.
For Boolean bit operations with only one operand the C-flag is always cleared. For
Boolean bit operations with two operands the C-flag represents the logical ANDing of the
two specified bits.
V-Flag:
For addition, subtraction and 2's complementation the V-flag is always set to
'1', if the result overflows the maximum range of signed numbers, which are
representable by either 16 bits for word operations ('–8000
H
' to '+7FFF
H
'), or by 8 bits for
byte operations ('–80
H
' to '+7F
H
'), otherwise the V-flag is cleared. Note that the result of
-EXCERPT-
C-Flag:
After an addition the C-flag indicates that a carry from the most significant bit
of the specified word or byte data type has been generated. After a subtraction or a
comparison the C-flag indicates a borrow, which represents the logical negation of a
carry for the addition.
This means that the C-flag is set to '1', if
no
carry from the most significant bit of the
specified word or byte data type has been generated during a subtraction, which is
performed internally by the ALU as a 2's complement addition, and the C-flag is cleared
when this complement addition caused a carry.
The C-flag is always cleared for logical, multiply and divide ALU operations, because
these operations cannot cause a carry anyhow.
For shift and rotate operations the C-flag represents the value of the bit shifted out last.
If a shift count of zero is specified, the C-flag will be cleared. The C-flag is also cleared
Bit
Function
N
Negative Result
Set, when the result of an ALU operation is negative.
C
Carry Flag
Set, when the result of an ALU operation produces a carry bit.
V
Overflow Result
Set, when the result of an ALU operation produces an overflow.
Z
Zero Flag
Set, when the result of an ALU operation is zero.
End of Table Flag
Set, when the source operand of an instruction is 8000
H
or 80
H
.
Multiplication/Division In Progress
‘
0
’
: There is no multiplication/division in progress.
‘
1
’
: A multiplication/division has been interrupted.
MULIP
USR0
User General Purpose Flag
May be used by the application software.
HLDEN,
ILVL, IEN
Interrupt and EBC Control Fields
Define the response to interrupt requests and enable external bus arbitration.
(Described in section
“
Interrupt and Trap Functions
”
)