By:
Masud-ul-Hasan

27

PSW
(Program Status Word)

•CY: (Carry Flag) is dual purpose: **(1)** As
traditional CY for arithmetic
operations e.g., If A contains FFH then the instruction **ADD A, #1**

leaves A equal to 00H and sets the CY in PSW. (A=00H & CY=1)

**(2)** As Boolean accumulator e.g., ANL C, 25H ; ANDs bit 25H with the carry flag and places the result back in the
CY.
•AC: (Auxiliary Carry Flag) used in addition of BCD numbers, is set if a carry was generated out of bit 3 into bit 4. If the
values are added are BCD, then
the add instruction must be followed by DAA (decimal adjust accumulator) to bring results greater
than 9 back into
range.
•F0: (Flag 0) is a general-purpose flag bit available for user applications.

leaves A equal to 00H and sets the CY in PSW. (A=00H & CY=1)