Program status word(PSW)

Flags: 1 bit registers provided to store the status of results of some instruction

: It is a flip flop

8051 has :

-4 math flags: Carry(CY), Auxiliary carry(AC), Overflow(OV), Parity(P)

-3 general purpose user flag:

1) Carry flag (CY) - Set when there is a carry or borrow out of the MSB (D7) of the result

2)Auxiliary carry ( AC) -Set when there is a carry out from lower nibble to higher nibble or borrow from higher nibble to lower nibble

3)Overflow flag(OV)-arithmetic overflow has occurred

4)Parity flag(P)-the result has even parity (even no. of 1's)

General purpose flags

-can be set 1 or 0 as programmer desires

-F0,GF0,GF! are the three general purpose flag

-F0 is in PSW and GF0 and GF1 are in PCON register

Program status word(PSW)

Conteúdo das notas (1)