XC68HC05P18A Motorola, XC68HC05P18A Datasheet - Page 38

• Manufacturer Part Number: XC68HC05P18A
• Description: HCMOS Microcontroller Unit
• Manufacturer: Motorola

Central Processor Unit (CPU)
3.4 Arithmetic/Logic Unit
Technical Data
38
Zero Flag
Carry/Borrow Flag
The arithmetic/logic unit (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
operations within the ALU. The multiply instruction (MUL) requires 11
internal clock cycles to complete this chain of operations.
The CPU sets the zero flag when an arithmetic operation, logical
operation, or data manipulation produces a result of $00.
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.
Central Processor Unit (CPU)
MC68HC05P18A
MOTOROLA