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EZ-USB FX2 Technical Reference Manual
Page 12-8 EZ-USB FX2 Technical Reference Manual v2.1
Table 12-4. PSW Register - SFR 0xD0
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. See the PSW Flags Affected column in
Table 12-2.
PSW.6 AC - Auxiliary carry flag. Set to 1 when the last arithmetic operation resulted in a carry into (dur-
ing addition) or borrow from (during subtraction) the high order nibble, otherwise cleared to 0 by
all arithmetic operations. See the PSW Flags Affected column in
Table 12-2.
PSW.5 F0 - User flag 0. Available to FX2 firmware for general purpose.
PSW.4 RS1 - Register bank select bit 1.
PSW.3 RS0 - Register bank select bit 0.
RS1:RS0 select a register bank in internal RAM:
RS1
RS0 Bank Selected
0 0 Register bank 0, addresses 0x00-0x07
0 1 Register bank 1, addresses 0x08-0x0F
1 0 Register bank 2, addresses 0x10-0x17
1 1 Register bank 3, addresses 0x18-0x1F
PSW.2 OV - Overflow flag. This is the signed carry bit. The OV flag is set when a positive sum exceeds
0x7F or a negative sum (in twos complement notation) exceeds 0x80. After a multiply, OV = 1 if
the result of the multiply is greater than 0xFF. After a divide, OV = 1 if a divide-by-0 occurred.
See the PSW Flags Affected column in
Table 12-2.
PSW.1 F1 - User flag 1. Available to FX2 firmware for general purpose.
PSW.0 P - Parity flag. Contains the modulo-2 sum of the 8 bits in the accumulator (i.e., set to 1 when the
accumulator contains an odd number of 1 bits, set to 0 when the accumulator contains an even
number of 1 bits).
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