The flags register is a special-purpose register in CPUs that indicates the processor's current state through various flag bits that are set or reset based on the results of arithmetic and logical operations. It includes status flags such as carry, auxiliary, zero, parity, and sign flags, each reflecting specific conditions like overflow or zero results. Control flags, like the interrupt and directional flags, manage processor responses to interrupts and data processing directions.

1. FLAGS
REGISTER

2. WHAT IS FLAGS REGISTER?
• Special registers. Because these are designed for
specific purposes and are distinct/different from
general purpose registers.
• Size and meaning of flag bits in flags register is
architecture dependent.
• Each bit represents a specific condition or state of
the processor.
• Determines the current state of processor .
• Depending upon the value of result after any
arithmetic and logical operation the flag bits become
set(1) or reset(0).

3. WHERE IS THE FLAGS REGISTER LOCATED?
FLAGS REGISTER
STATUS
REGISTER
Status register is a
special-purpose register
that holds various
status flags that reflect
the current state of the
CPU. The status register
is usually located
within the CPU's
control unit.
CONTROL UNIT
Control unit is
responsible for
managing the
execution of
instructions.
In most CPU
architectures, flag
registers are a
part of the CPU's
status register.

4. •Also called conditional
flags.
•are set (1) or reset(0)
depending upon condition
after operation.
01
STATUS FLAGS
02
•Enable or disable
certain operations of
the microprocessor.
CONTROL FLAGS
TYPES OF FLAGS REGISTER

5. 1. Carry
Flag(CF)
STATUS FLAGS
• is set to 1 when the 9th bit is
generated while performing
any arithmetic operation on
unsigned 8-bit set/sequence.
•If the bits are in the
range -128 to +127 the
OF=0 otherwise OF=1.
• Or you can say OF is
set 1 when there is
a signed overflow.
3. Auxiliary
Flag(AF)
• set to 1 when there
is an unsigned
overflow for low
nibble(half of a bit/ 4
bits).
5. Zero
Flag(ZF)
• set to 1 when the
result is zero.
• set to 0 when result
is non-zero.
4. Parity
Flag(PF)
•is set to 1 when there is
even number of one(1)
bits in the result.
•0 when there is odd
number of 1 bits in
result.
6. Sign
Flag(SF)
• It takes the value of
most significant bit.
• 1 when result is
negative.
• 0 when result is
positive.
Carry Flag (CF) Overflow Flag (OF) Auxiliary Flag (AF)
Zero Flag (ZF) Parity Flag (PF) Sign Flag (SF)

6. +
Carry flag example:

7. +
1
Auxiliary carry flag example:

8. •Is a processor flag that
controls whether interrupts
are enabled or disabled.
When the interrupt flag is
set to 1, interrupts are
enabled, which means that
the processor can receive
and respond to interrupts.
When the interrupt flag is
set to 0, interrupts are
disabled, which means that
the processor will not
respond to interrupts.
CONTROL FLAGS
• • used by some
instructions to
process data chains.
• when this flag is set
to 0, the processing
is done forwards
meaning front to
back.
• when this flag is set
to 1, the processing is
done backwards
meaning back to
front.
Trap Flag (TF) Interrupt Flag (IF) Directional Flag (DF)
•A trap is a software
interrupt that is triggered
by the program itself,
typically for the purpose of
handling an error or an
exception.
•when set to 1 the traps are
enabled otherwise 0