Notes
Program status word(PSW)
Content of the notes (1)
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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