What is the function of the program status register PSW of the MCS-51 microcontroller?

What is the function of the program status register PSW of the MCS-51 microcontroller? What are the bits of the commonly used flags? What is their function?

Answer: PSW is an 8-bit register used to set the CPU status and indicate the status after instruction execution.

CY (PSW.7): ​​Carry flag. When executing addition or subtraction instructions, if the highest bit (D7) of the operation result has a carry or borrow, CY is automatically set to 1 by hardware.

AC (PSW.6): Half carry flag, also known as auxiliary flag. When executing addition and subtraction instructions, if the lower half byte (D3) of the operation result has a carry or borrow to the upper half byte, AC is automatically set to 1 by hardware.

F0, F1 (PSW.5 and PSW.1): User flag bits. Users can assign certain meanings to F0 and F1 as needed, and set them to 1 or clear them to 0 as software flags.

RS1, RS0 (PSW.4 and PSW.3): Working register group selection control bits. By setting these two bits, one of the four working register groups can be selected as the current working register.

OV (PSW.2): Overflow flag. There are two situations that affect this bit. First, when performing addition or subtraction operations, if any one of D7 or D6 has a carry or borrow, OV is automatically set to 1.

P (PSW.0): Parity flag. After each instruction is executed, this bit will indicate the number of 1s in the current accumulator A. If there is an odd number of 1s in A, P is automatically set to 1.