Table B-6. PSW Register - SFR D0h
Bit
Function
PSW.7
CY - Carry flag. This is the unsigned carry bit. The CY flag is
set when an arithmetic operation results in a carry from bit 7 to
bit 8, and cleared otherwise. In other words, it acts as a virtual
bit 8. The CY flag is cleared on multiplication and division.
PSW.6
AC - Auxiliary carry flag. Set to 1 when the last arithmetic
operation resulted in a carry into (during addition) or borrow
from (during subtraction) the high order nibble, otherwise
cleared to 0 by all arithmetic operations.
PSW.5
PSW.4
PSW.3
F0 - User flag 0. Bit-addressable, general purpose flag for
software control.
RS1 - Register bank select bit 1. used with RS0 to select a
register bank in internal RAM.
RS0 - Register bank select bit 0, decoded as:
RS1 RS0 Banks Selected
0
0
1
1
0
1
0
1
Register bank 0, addresses 00h-07h
Register bank 1, addresses 08h-0Fh
Register bank 2, addresses 10h-17h
Register bank 3, addresses 18h-1Fh
PSW.2
OV - Overflow flag. This is the signed carry bit. The OV flag
is set when a positive sum exceeds 7fh, or a negative sum (in
two’s compliment notation) exceeds 80h. On a multiply, if OV
= 1, the result of the multiply is greater than FFh. On a divide,
OV = 1 on a divide by 0.
PSW.1
PSW.0
F1 - User flag 1. Bit-addressable, general purpose flag for
software control.
P - Parity flag. Set to 1 when the modulo-2 sum of the 8 bits in
the accumulator is 1 (odd parity), cleared to 0 on even parity.
B - 16
Appendix B: 8051 Architectural Overview
EZ-USB TRM v1.9
CYPRESS [ CYPRESS ]
