mc68hc05pv8a Freescale Semiconductor, Inc, mc68hc05pv8a Datasheet - Page 47

• Manufacturer Part Number: mc68hc05pv8a
• Description: Mc68hc05pv8a Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

3.3 Arithmetic/Logic Unit (ALU)
MC68HC(8)05PV8/A — Rev. 1.9
Interrupt Mask
Setting the interrupt mask disables interrupts. If an interrupt request
occurs while the interrupt mask is logic zero, the CPU saves the CPU
registers on the stack, sets the interrupt mask, and then fetches the
interrupt vector. If an interrupt request occurs while the interrupt mask is
set, the interrupt request is latched. Normally, the CPU processes the
latched interrupt as soon as the interrupt mask is cleared again.
A return from interrupt (RTI) instruction pulls the CPU registers from the
stack, restoring the interrupt mask to its cleared state. After any reset,
the interrupt mask is set and can be cleared only by a software
instruction.
Negative Flag
The CPU sets the negative flag when an arithmetic operation, logical
operation, or data manipulation produces a negative result.
Zero Flag
The CPU sets the zero flag when an arithmetic operation, logical
operation, or data manipulation produces a result of $00.
Carry/Borrow Flag
The CPU sets the carry/borrow flag when an addition operation
produces a carry out of bit 7 of the accumulator or when a subtraction
operation requires a borrow. Some logical operations and data
manipulation instructions also clear or set the carry/borrow flag.
The ALU performs the arithmetic and logical operations defined by the
instruction set.
The binary arithmetic circuits decode instructions and set up the ALU for
the selected operation. Most binary arithmetic is based on the addition
algorithm, carrying out subtraction as negative addition. Multiplication is
not performed as a discrete operation but as a chain of addition and shift
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Arithmetic/Logic Unit (ALU)
CPU and Instruction Set
Technical Data