Maxim Integrated MAXQ610 - Manual (Page 46)

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MAXQ610 User’s Guide
3.6.2 Zero Flag
The zero flag (PSF .7) is a dynamic flag that reflects the current state of the active accumulator Acc . If all bits in the
active accumulator are zero, the zero flag equals 1 . Otherwise, it equals 0 .
Because the zero flag is a dynamic reflection of (Acc = 0), any instruction that changes the value in the active accu-
mulator can potentially change the value of the zero flag . Any instruction that changes which accumulator is the active
one (including AP autoincrement/decrement) can also change the zero flag .
The following operations use the zero flag:
• JUMP Z, src
(jump if zero flag is set)
• JUMP NZ, src (jump if zero flag is cleared)
3.6.3 Equals Flag
The equals flag (PSF .0) is a static flag set by the CMP instruction . When the source given to the CMP instruction is
equal to the active accumulator, the equals flag is set to 1 . When the source is different from the active accumulator,
the equals flag is cleared to 0 .
The following instructions use the value of the equals flag . Note that the ‘src’ for the JUMP E/NE instructions must be
immediate .
• JUMP E, src
(jump if equals flag is set)
• JUMP NE, src (jump if equals flag is cleared)
In addition to the CMP instruction, any instruction using PSF as the destination can alter the equals flag .
3.6.4 Carry Flag
The carry flag (PSF .1) is a static flag indicating that a carry or borrow bit resulted from the last ADD/ADDC or SUB/
SUBB operation . Unlike the other status flags, it can be set or cleared explicitly, and is also used as a generic bit
operand by many other instructions .
The following instructions can alter the carry flag:
• ADD src
(Add source to active accumulator)
• ADDC src (Add source and carry to active accumulator)
• SUB src (Subtract source from active accumulator)
• SUBB src (Subtract source and carry from active accumulator)
• SLA, SLA2, SLA4 (Arithmetic shift left active accumulator)
• SRA, SRA2, SRA4 (Arithmetic shift right active accumulator)
• SR (Shift active accumulator right)
• RLC/RRC (Rotate active accumulator left/right through carry)
• MOVE C, Acc. (Set Carry to selected active accumulator bit)
• MOVE C, #i (Explicitly set, i = 1, or clear, i = 0, the carry flag)
• CPL C (Complement carry)
• MOVE C, src. (Copy bit addressable register bit to carry)
• any instruction using PSF as the destination
The following instructions use the value of the carry flag:
• ADDC src
(Add source and carry to active accumulator)
• SUBB src (Subtract source and carry from active accumulator)
• RLC/RRC (Rotate active accumulator left/right through carry)
• CPL C (Complement carry)