Question

Draw the labelled diagram of X-86 farilily Flag Register.

Answer 1

The microprocessor 8086 has 16-bit register with 9 active flages, which are shown in following figure.

Where,
Cy - Carry flag
P - Parity flag
AC - Auxiliary carry flag
Z - Zero flag
S - Sign flag
TF - Trap flag
IF - Interrupt flag
DF - direction flag
OF - over flow flag

  The first five bits are identical to 8085.
  In data flag category OF (Overflow) flag is there, rests of the flags are same as 8085 flags.

• OF– Overflow Flag– Used in signed numbers, when the result of signed number is too large, causing MSB to overlfow into the sign bit, this flag is set.
•  DF – Direction Flag – Used to control the direction (increment/decrement) of the string operation.
•  IF – Interrupt Flag – Used to enable or disable external maskable interrupt requests.
•  TF – Trap Flag – Used for single stepping instructions