Answer Posted / sushil kumar
flags are used to test data conditions.
For example, after an addition of two numbers, if the sum in
the accumulator id larger
than eight bits, the flip-flop uses to indicate a carry --
called the Carry flag (CY) -- is
set to one. When an arithmetic operation results in zero,
the flip-flop called the
Zero(Z) flag is set to one. The first Figure shows an 8-bit
register, called the flag
register, adjacent to the accumulator. However, it is not
used as a register; five bit
positions out of eight are used to store the outputs of the
five flip-flops. The flags are
stored in the 8-bit register so that the programmer can
examine these flags (data
conditions) by accessing the register through an instruction.
These flags have critical importance in the decision-making
process of the microprocessor.
The conditions (set or reset) of the flags are tested
through the software
instructions. For example, the instruction JC (Jump on
Carry) is implemented to
change the sequence of a program when CY flag is set. The
thorough understanding
of flag is essential in writing assembly language programs.
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