Maxim Integrated MAXQ622 - Manual (Page 63)

MAXQ612/MAXQ622 User’s Guide
Maxim Integrated 4-7
REGISTER DESCRIPTION
PSF, 08h[04h] Processor Status Flags Register (8 bits)
Initialization This register is cleared to 80h on all forms of reset .
Access Bit 7 (Z) and bit 6 (S) are read-only .
Bits 4, 3 (GPF1, GPF0), bit 2 (OV), bit 1 (C) and bit 0 (E) are unrestricted read/write .
PSF.0 (E) Equals Flag. This bit flag is set to 1 whenever a compare operation (CMP) returns an
equal result . If a CMP operation returns not equal, this bit is cleared .
PSF.1 (C) Carry Flag. This bit flag is set to 1 whenever an addition or subtraction operation (ADD,
ADDC, SUB, SUBB) returns a carry or borrow .
This bit flag is cleared to 0 whenever an addition or subtraction operation does not return a
carry or borrow .
PSF.2 (OV) Overflow Flag. This flag is set to 1 if there is a carry out of bit 14 but not out of bit 15, or
a carry out of bit 15 but not out of bit 14 from the last arithmetic operation, otherwise, the
OV flag remains as 0 . OV indicates a negative number resulted as the sum of two positive
operands, or a positive sum resulted from two negative operands .
PSF.3 (GPF0) General-Purpose Flag 0
PSF.4 (GPF1) General-Purpose Flag 1. General-purpose flag bits are provided for user software control .
PSF.5 Reserved . Reads return 0 .
PSF.6 (S) Sign Flag. This bit flag mirrors the current value of the high bit of the active accumulator
(Acc .15) .
PSF.7 (Z) Zero Flag. The value of this bit flag equals 1 whenever the active accumulator is equal to
zero, and it equals 0 otherwise .