Program status word (psw) – Maxim Integrated High-Speed Microcontroller Users Guide: Network Microcontroller Supplement User Manual
Page 75
High-Speed Microcontroller User’s
Guide: Network Microcontroller
Supplement
75
Program Status Word (PSW)
R = Unrestricted read, W = Unrestricted write, -n = Value after reset
7
6
5
4
3
2
1
0
SFR D0h
CY
AC
F0
RS1
RS0
0V
F1
P
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
RW-0
CY
Bit 7
AC
Bit 6
F0
Bit 5
RS1, RS0
Bits 4-3
Carry flag. This bit is set if the last arithmetic operation resulted in a carry (during addition) or a borrow
(during subtraction). Otherwise, it is cleared to 0 by all arithmetic operations.
Auxiliary carry flag. This bit is set to 1 if the last arithmetic operation resulted in a carry into (during
addition) or a borrow from (during subtraction) the high-order nibble. Otherwise, it is cleared to 0 by all
arithmetic operations.
User flag 0. This is a bit-addressable, general-purpose flag for software control.
Register bank select 1-0. These bits select which register bank is addressed during register accesses.
RS1
RS0
REGISTER
BANK
ADDRESS
0
0
0
00h–07h
0
1
1
08h–0Fh
1
0
2
10h–17h
1
1
3
18h–1Fh
OV
Bit 2
F1
Bit 1
P
Bit 0
Overflow flag. This bit is set to 1 if there is a carry-out of bit 6 but not out of bit 7, or if there is a carry-
out of bit 7 but not out of bit 6 for addition. When adding signed integers, OV indicates a negative num-
ber resulted as the sum of two positive operands or a positive sum from two negative operands. OV is
set if a borrow is needed into bit 6 but not into bit 7, or if a borrow is needed into bit 7 but not into bit 6
for subtraction. When subtracting signed integers, OV indicates a negative number produced when a
negative value is subtracted from a positive value or a positive result when a positive value is subtract-
ed from a negative value. OV is also set if the product is greater than 0FFh for multiplication. This bit is
always cleared for division operations.
User flag 1. This is a bit-addressable, general-purpose flag for software control.
Parity flag. This bit is set to 1 if there is an odd number of 1’s in the accumulator and is cleared to 0 if
there is an even number of 1’s in the accumulator.
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